Displays

Surface tension influences the fraction of atmospheric particles that become cloud droplets. Recent field studies have indicated that surfactants, which lower the surface tension of macroscopic solutions, are an important component of aerosol mass. However, the surface tension of activating aerosol particles is still unresolved, with most climate models assuming activating particles have a surface tension equal to that of water. For surfactants to be relevant to particle activation into cloud droplets, multiple parameters must be considered. First, the concentration of surfactant in the initial particle must be sufficiently large that surface tension depression is maintained during activation, despite the dilution that occurs as water condenses onto the particle. Second, the high surface to volume ratio of micron and submicron particles necessitates partitioning a larger fraction of the surfactant molecules to the particle surface than in a typical solution, resulting in a depletion of the bulk concentration and an increase in the surface tension relative to a bulk sample. Third, the timescale for establishing equilibrium at the droplet surface must be known. The interplay of these parameters highlights the necessity of direct measurements of picolitre droplet surface tension.

This presentation will describe two cutting-edge approaches we have developed to directly measure the surface tension of microscopic droplets. In the first approach, ejection of ~20 µm radius surfactant-containing droplets from a dispenser excites oscillations in droplet shape that can be used to retrieve the droplet surface tension on microsecond timescales. These measurements allow investigation of surfactant partitioning timescales in aerosol and, crucially, test the assumption that droplet surfaces are generally in their equilibrium state. In the second approach, the coalescence of ~8 µm radius droplets is investigated. Coalescence excites droplet shape oscillations which again permit quantification of droplet surface tension. We demonstrate that surfactants can significantly reduce the surface tension of finite sized droplets below the value for water, consistent with recent field measurements. This surface tension reduction is droplet size dependent and does not correspond exactly to the macroscopic solution value. A new monolayer partitioning model confirms the observed size dependent surface tension arises from the high surface-to-volume ratio in finite-sized droplets and enables predictions of aerosol hygroscopic growth. This model, constrained by the laboratory measurements, is consistent with a reduction in critical supersaturation for activation and a 30% increase in cloud droplet number concentration, in line with a radiative cooling effect larger than current estimates assuming a water surface tension by 1 W·m^-2. The results imply that one single value for surface tension cannot be used to predict the activated aerosol fraction.

How to cite: Bzdek, B., Miles, R., Malila, J., Boyer, H., Walker, J., Reid, J., Dutcher, C., and Prisle, N.: Surface Tension of Surfactant-Containing, Finite Volume Droplets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-106, https://doi.org/10.5194/egusphere-egu2020-106, 2020.

The depolarisation ratio of heavily coated soot particles was previously found to be sensitive to the chemical composition of the coating material, which is reflected by the refractive index. Employing the Discrete Dipole Approximation code ADDA optical calculations were performed with a set of heavily coating soot aggregates with two different coating materials at 355 nm, 532 nm, and 1064 nm. As coating materials sulphate and a toluene-based material were assumed. The soot aggregates were modelled based on results reported from in-situ field measurements and using a coating model, which allows for a tunable transition between film coating and spherical shell coating. The aggregates’ size was varied by increasing the number of soot monomers inside each aggregate from 26 to 1508 in linearly equidistant steps.

Size-averaged lidar-measureable quantities for the coated aggregates, such as the linear depolarisation ratio, the extinction-to-backscatter ratio (lidar ratio), and the Ångström exponents of the extinction coefficient, the backscatter coefficient, and the extinction-to-backscatter ratio were calculated, and the error of the simulations was estimated. With the exception of the linear depolarisation ratio at 1064 nm these observables do not overlap within the estimated error bounds. As the coating materials result in clearly distinguishable lidar observables, information on the chemical composition of coated soot aerosol can potentially be inferred from lidar measurements.

How to cite: Kanngiesser, F. and Kahnert, M.: Coating material-dependent differences in modelled lidar-measurable quantities for heavily coated soot particles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-299, https://doi.org/10.5194/egusphere-egu2020-299, 2020.

The hydroxyl radical (OH) is the main oxidant in the troposphere and is vitally important for its role in the removal of greenhouse gases such as methane from the atmosphere. Moreover, the OH radical also has a role in the formation of secondary pollutants such as tropospheric ozone and secondary organic aerosols (SOAs), formed via the oxidation of volatile organic compounds (VOCs). Understanding the sources and sinks of OH within the atmosphere is therefore crucial in order to fully understand the concentration and distribution of trace atmospheric species associated with climate change and poor air quality.

In polluted environments the dominant source of OH to initiate oxidation is the photolysis of nitrous acid (HONO). Current atmospheric chemistry models underestimate the concentration of HONO indicating a potential missing tropospheric source of HONO. There is a large uncertainty in the production of HONO from the contribution and role of aerosols and heterogeneous chemistry both under light and dark conditions.

In order to investigate the missing source of HONO from illuminated aerosols and determine its atmospheric relevance, a photo-fragmentation laser induced fluorescence (PF-LIF) instrument coupled to an aerosol flow tube system has been constructed. The PF-LIF instrument provides a highly sensitive measurement of HONO by fragmenting it into OH which is then detected in a low pressure cell by LIF. The aim of this system is to measure the rate of production of HONO from illuminated aerosol surfaces.

We will present an overview of the PF-LIF instrument and results from experiments investigating the reactive uptake of NO₂ by TiO₂ aerosols to produce HONO. The change in the reactive uptake coefficient as a function of NO₂ concentration and the dependence of HONO production on relative humidity and light intensity will also be discussed.   

How to cite: Dyson, J., Boustead, G., Fleming, L., Blitz, M., Stone, D., Arnold, S., Whalley, L., and Heard, D.: Photo-Induced Heterogeneous Chemistry of Reactive Species on Aerosol Surfaces: Using Photo-Fragmentation Laser Induced Fluorescence for the Measurement of Nitrous Acid Production from Titanium Dioxide Aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2369, https://doi.org/10.5194/egusphere-egu2020-2369, 2020.

This study focuses on the effect of surface film thickness on the ozone reaction kinetics of films of a self-assembled unsaturated fatty acid aerosol proxy coated inside quartz capillaries. It also reveals evidence for reaction stagnation and stopping for the thickest films, leaving a significant amount of unreacted material and suggesting that an inert product is formed during the course of the reaction. These findings have implications for the atmospheric lifetime of such a system.

The oleic acid-ozone reaction is used as the model system for heterogeneous oxidation reactions in organic aerosols. Major sources of oleic acid in the atmosphere include marine and cooking emissions. Oxidation of organic aerosols is known to affect Cloud Condensation Nuclei (CCN) generation and therefore cloud formation. It follows that factors affecting aerosol reactivity have an effect on cloud formation potential and therefore also on the climate.

In our experiments, oleic acid is mixed with its sodium salt (sodium oleate) to form a highly viscous self-assembled lamellar phase system observable using a synchrotron-based technique: Small Angle X-ray Scattering (SAXS). Here, we take advantage of intense synchrotron radiation to probe our coated capillary films. We use the observed decay of the self-assembled scattering peak as a function of time exposed to ozone. We have obtained ~50 kinetic decay parameters spanning a range of film thicknesses, showing a drastic increase in reaction kinetics with decreasing film thickness.

There is a linear relationship between increasing film thickness and amount of self-assembled material (reactant) remaining at the end of the reaction. This implies that a reaction product hinders further reactivity and that this product may take a while to form, explaining the occurrence only in thicker films.

Modelling studies will help us understand the mechanism behind these observations and to relate to a previously-postulated idea of an inert “crust” of products forming on the surface of this viscous aerosol proxy (Pfrang et al., Atmos. Chem. Phys., 2011, 11, 7343-7354).

In summary, we demonstrate thickness-dependent reaction kinetic parameters which vary significantly with film thickness, implying that the atmospheric lifetime for a film is sensitive to the film thickness. We present evidence for reaction stagnation by an as of yet unknown inert product. Kinetic modelling is ongoing in order to explain these findings.

How to cite: Milsom, A., Squires, A. M., Ward, A. D., Terrill, N. J., and Pfrang, C.: Thickness-Dependent Oxidation Kinetics of Coated Films of a Self-Assembled Unsaturated Fatty Acid Aerosol Proxy with Evidence for Inert “Crust” Formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10982, https://doi.org/10.5194/egusphere-egu2020-10982, 2020.

The interactions among low and semi-volatile organic compounds, water and other inorganic components within fine-mode aerosols are complex. We show that understanding several features of this complexity can be important in the context of phase separation, a particle surface composition enriched by organics and for related cloud droplet activation modeling.  
Context: oxidized organic compounds contribute to the particle hygroscopicity, yet typically to a lesser extent than dissolved inorganic ions. The overall hygroscopicity of aerosols in turn greatly affects their water uptake in an air parcel experiencing increasing relative humidity. The mechanism acts directly in terms of adding water mass, as well as indirectly via a hygroscopicity-induced feedback leading to enhanced gas–to–particle partitioning of semi-volatile organic components alongside a re-equilibration of the aerosol with inorganic acids, ammonia and further water uptake. Furthermore, non-ideal mixing may induce liquid–liquid phase separation, often leading to an organic-rich phase of relatively low surface tension surrounding an inorganic-rich particle core. This phase separation effect and related surface enhancements of organic component concentrations affect not only the morphology but also the potential for near-surface chemical reactions, as well as the thermodynamics controlling an aerosol particle’s activation into a cloud droplet at realistic water vapour supersaturations.  New experimental techniques and field observations over the past few years have encouraged model development for an improved representation of these processes on a detailed level (see, e.g., discussion in Davies et al., 2019). This has led to a better understanding of the potential role of organic aerosol compounds spanning a range of polarities and an associated evolution of surface tension prior to the cloud condensation nucleus (CCN) activation point. While detailed process models still lack finer details to fully capture these composition and phase effects reliably and predictively, important challenges exist in translating these mechanisms into computationally efficient and feasible reduced-complexity models of use for air quality and chemistry-climate modelling.
In this presentation, we will outline the current state of a relatively complete process-level aerosol thermodynamics model based on AIOMFAC and introduce key features of a recently developed reduced-complexity organic aerosol model that accounts for water content and hygroscopicity-induced feedbacks on composition (Gorkowski et al., 2019). A key advantage of the reduced-complexity model is its ability to use only input typically known from field measurements or data available in large-scale air quality models. Our approach is compatible with a volatility basis set approach and allows for extending it by adding a realistic humidity dependence. In addition, we account for phase separation and related effects on surface tension in a simplified, computationally efficient manner. This approach and its results for aerosol hygroscopicity and cloud droplet activation will be discussed.

References:

Davies, J. F., Zuend, A., and Wilson, K. R.: Technical note: The role of evolving surface tension in the formation of cloud droplets, Atmos. Chem. Phys., 19, 2933–2946, doi:10.5194/acp-19-2933-2019, 2019.

Gorkowski, K., Preston, T. C., and Zuend, A.: Relative-humidity-dependent organic aerosol thermodynamics via an efficient reduced-complexity model, Atmos. Chem. Phys., 19, 13383–13407, 10.5194/acp-19-13383-2019, 2019.

How to cite: Zuend, A. and Gorkowski, K.: Modelling hygroscopicity-induced gas–aerosol partitioning, organic surface enrichment and cloud droplet formation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12463, https://doi.org/10.5194/egusphere-egu2020-12463, 2020.

Clouds are made of droplets that arise from the activation of suitable aerosol particles (termed cloud condensation nuclei, CCN). In the activation process, water vapor saturation ratio exceeds a critial ratio enabling CCN runaway-growth to cloud droplet sizes. The number concentration of cloud droplets (CDNC) is highly dependent on the aerosol population properties (size distribution and composition), relative humidity, and the vertical wind component. While the activation of CCN consisting of non-volatile particulate matter is fairly well understood, the same process involving semi-volatile organic vapors (SVOCs) has received less attention despite their significant presence in ambient air. A recent cloud parcel modeling study shows substanial CDNC enhancement due to SVOC condensation (Topping et al., 2013). Surprisingly, the topic has not been widely investigated nor the results replicated with other cloud parcel models (CPM). Thus, in the current study we seek to quantify the CDNC enhancement by SVOC condensation using a recently developed CPM framework (Lowe et al., 2020, in prep.). Moreover, the CPM initialization is performed, for the first time, with state-of-the art measurement data including measured SVOC data for multiple airmass types.

Here, the CPM, which uses spectral microphysics for the simulation of CCN activation and hydrometeor growth, also includes a SVOC condensation equation analogous to those of water vapor. Equilibrium initialization of the SVOC volatility basis set (VBS) partitioning coefficients is performed iteratively, and constrained by the organic to inorganic ratio in the particle phase determined by ambient measurements performed at the Chacaltaya Global Atmospheric Watch (GAW) Station located at 5240 m a.s.l. in the Bolivian Andes, in spring 2018. The uniquely comprehensive data set recorded, which tracks all of the relevant aerosol population characteristics in near real-time, reveals a high degree of variability in aerosol composition, size distribution and loading depending on the air mass origin. Lagrangian backward simulations during the measurement period at Chacaltaya GAW reveal at least 18 significantly different airmass origins (Aliaga et al., 2020, in prep.). Such variability served multiple model initialization scenarios for individual case studies. We will show a suite of CDNC enhancements by SVOC condensation under different initialization scenarios actualized in data recorded at Chacaltaya GAW Station, including airmasses originating from the Amazon (biomass burning and biogenic VOCs), Andean plateau (volcanic activity), and La Paz/El Alto metropolitan areas (anthropogenic emissions).

References:

How to cite: Heikkinen, L., Lowe, S., Wu, C., Aliaga, D., Huang, W., Gramlich, Y., Carbone, S., Zha, Q., Velarde, F., Mardoñez, V., Moreno, I., Koenig, A., Andrade, M., Artaxo, P., Bianchi, F., Krejci, R., Ehn, M., Partridge, D., Riipinen, I., and Mohr, C.: Quantifying the effect of SVOC condensation on cloud droplet number in different airmass types, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10491, https://doi.org/10.5194/egusphere-egu2020-10491, 2020.

Cloud Condensation Nuclei (CCN) and other aerosol properties were investigated in Delhi, India, from Feb. to Mar. 2018. The high anthropogenic influence on aerosol was studied with size-resolved CCN measurements (supersaturation (S) between 0.13 to 0.66% and selected diameters from 10 to 300 nm). Furthermore the chemical composition (Aerosol Chemical Speciation Monitor and Aethalometer AE33) of the particles was measured. The aerosol number size distribution was derived by size data inversion of Differential Mobility Particle Sizer (DMPS) from size-resolved CCN measurements. Based on multi-year back trajectory (BT) data, a spatial clustering analysis was done for the actual campaign period and two distinct clusters were identified: northwest- west northwest-long range transport (NW-LRT) and south-southeast-east southeast (SE).

There was preponderant organic mass fraction (f_org) in the aerosols throughout the campaign, with prominent diurnal variation except during the SE period. Pronounced diurnal variation was observed also in black carbon (BC) with an average concentration of 16 µg/m³ during NW-LRT, in contrast to a weak diurnal cycle with lower average concentration of 8 µg/m³ during SE. During the NW-LRT cluster the air masses traversed over agriculture fields with biomass burning (BB) activities identified using the fire radiative power (FRP) observations of Copernicus Atmosphere Monitoring Service (CAMS) Global Fire Assimilation System (GFAS). So it can be speculated that the BB emissions from the fields have contributed to enhanced BC concentrations during this period over Delhi. The remaining period, showing a mixture of local and long-range transported emissions also had a BC concentration higher than SE period when only local/regional emissions were observed. This is an important insight into the air pollution apocalypse in Delhi.

The overall average values of critical dry diameter (D_c) for CCN activation varied from 54 ± 8 nm at S = 0.66% to 139 ± 12 nm at S = 0.13%.The hygroscopicity parameter derived from CCN data (к_CCN) was in the range from 0.1 to 0.9 with an arithmetic mean of 0.27 ± 0.10, which is close to that of Beijing, another polluted continental region (0.31 ± 0.08, Gunthe et al., 2011). к_CCN also shows good agreement with the hygroscopicity parameter derived from the chemical composition measurements. A linear fit (Gunthe et al., 2009) applied to the relationship between refractory/non-refractory organic mass fraction and к_CCN at S = 0.13%, gives an effective hygroscopicity parameter к_org = 0.17 ± 0.09 and к_inorg = 0.80 ± 0.09, when extrapolated to f_org = 1 and f_org = 0, respectively. The presence of externally mixed inactive CCN particles is indicated by an average maximum activated fraction (MAF) of 0.82 ± 0.17 at S = 0.13%. The overall average D_c, к_CCN, and MAF did not vary much between NW-LRT and SE periods, although the particle number concentration was higher during NW-LRT. Moreover, high CCN efficiency was observed during NW-LRT, in spite of its enhanced BC concentration, indicating the presence of aged internally mixed aerosols. Further details will be presented.

How to cite: S. Raj, S., L. Pӧhlker, M., Klimach, T., Förster, J.-D., Walter, D., O. Krüger, O., Pӧhlker, C., Panda, U., Sharma, A., Derbyshire, E., D. Allan, J., Krishna R., R., Soni, V. K., Singh, S., Mcfiggans, G., Coe, H., Pӧschl, U., and S. Gunthe, S.: Impact of Long-Range Transport Biomass Burning (BB) Emissions on Cloud Condensation Nuclei (CCN) Activation in Continental Polluted Air of Delhi, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12744, https://doi.org/10.5194/egusphere-egu2020-12744, 2020.

Airborne bacteria are important components of biological aerosols. They have been shown to remain alive and metabolically active in the different compartment of the atmosphere (clouds, rain, aerosols), despite the harsh environmental conditions (U.V., free radicals, low temperatures, etc…). Current knowledge indicates that bacteria interfere with chemical reactivity in clouds, by utilizing carbon and nitrogen compounds, detoxifying free radicals and their precursors, etc. Nevertheless, due to the low biomass (≈ 10² to ≈10⁶ cells/m3) and numerous sampling constraints, bacterial activity remains largely unexplored in atmospheric water; and regarding atmospheric chemistry, airborne bacteria are still essentially regarded as inert particles.

To fulfill this gap in knowledge, this study aims at quantifying microbial activity in the different compartments of the atmosphere. Sampling and analytical methods were developed and adapted to overcome the low biomass constraint and the required immediate analyses, to obtain in situ quantitative and qualitative measurements of biological activity. Samplings of cloud water were performed between September 2019 and April 2020 at the Puy de Dôme Mountain’s meteorological station (1465 m asl, France) using impactors and high-flow-rate impingers [1], whereas precipitations were collected below the summit (Opme station, 680 m asl) using an automated wet-deposition sampler. Bacterial metabolic activity was assessed by coupling two different approaches: the determination of the active fraction of bacteria using the ubiquitous esterase enzyme activity as proxy (fluorescein diacetate assay, flow cytometry), and the quantification of ribosomal DNA/RNA (qPCR). Relationship between these activities and meteorological, physical and chemical measurements were also examined.

Preliminary results showed traces of a recent metabolic activity in cloud’s bacterial communities, as highlighted by the observed rRNA/rDNA ratio of 1. In parallel, 8.5% of the bacteria in clouds exhibited an esterase activity, supporting that bacteria can remain active in clouds. The bacterial fraction displaying esterase activity in precipitation samples was much higher (30%), suggesting fast variations in bacterial metabolic activity, probably related with changes in environmental constraints and bacterial assemblage composition. Further investigations are on-going to specify microbial activity along the aerosol-cloud-precipitation continuum, its variability, and to quantify its contribution to atmospheric chemical processes.

[1]           T. Šantl-Temkiv et al., “High-Flow-Rate Impinger for the Study of Concentration, Viability, Metabolic Activity, and Ice-Nucleation Activity of Airborne Bacteria,” Environ. Sci. Technol., vol. 51, no. 19, pp. 11224–11234, 2017.

How to cite: Rossi, F., Péguilhan, R., Brissy, M., Deguillaume, L., Delort, A.-M., and Amato, P.: Microbial metabolic activity measurements in clouds and precipitation at the puy de Dôme station (Central France), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9131, https://doi.org/10.5194/egusphere-egu2020-9131, 2020.

It is known that microorganisms are present in the outdoor atmosphere, in clouds and precipitation. These microorganisms originate from various local and distant sources and consist of very diverse and ephemeral communities. The most abundant bacterial taxa typically include Alpha-, Beta- and Gamma-Proteobacteria, with notably Pseudomonas and Sphingomonas among the dominant genera observed. Still, very little is known about their sources, metabolic activity, distribution, and their dynamics during their atmospheric life cycle. It was proposed in the past that bacteria with high ice nucleation activity are likely more efficiently precipitated than others [1]. Here, we extend this hypothesis and suggest more generally that different bacteria taxa could exhibit different phase partitioning between aerosol particles, cloud and rainwater, which may affect their atmospheric residence times. This implies that microorganisms are not equally distributed among the different atmospheric compartments (clouds, aerosols and precipitation).

To investigate this hypothesis, cloud and rain samples were collected simultaneously from single precipitation events, from two meteorological stations located at different altitudes: the summit of puy de Dôme Mountain (1465 m above sea level; France), embedded in clouds, using cloud impactors and high-flow-rate impingers [2], and below the summit, at Opme Station (680 a.s.l.) where precipitation occurred, using automated precipitation collector. The bacterial biodiversity was examined by 16s rRNA gene amplicon MiSeq sequencing. Samples were also characterized for their chemical contents. We show that clouds and precipitation host distinct microbial communities. Clouds host communities from high altitude likely to be of distant origin, while precipitation also includes material originating from the air column underneath and from local origin. So, comparing the biodiversity hosted in clouds and precipitation within single air masses provides information on the relative contribution of local and distant sources to the microorganisms deposited at the surface with rainfalls, and provides very new information concerning the processing and fate of bacteria in the atmosphere.

[1]         M. Joly, P. Amato, L. Deguillaume, M. Monier, C. Hoose, and A. M. Delort, “Quantification of ice nuclei active at near 0 °c temperatures in low-altitude clouds at the Puy de Dôme atmospheric station,” Atmos. Chem. Phys., vol. 14, no. 15, pp. 8185–8195, 2014.

[2]         T. Šantl-Temkiv et al., “High-Flow-Rate Impinger for the Study of Concentration, Viability, Metabolic Activity, and Ice-Nucleation Activity of Airborne Bacteria,” Environ. Sci. Technol., vol. 51, no. 19, pp. 11224–11234, 2017.

How to cite: Péguilhan, R., Besaury, L., Rossi, F., Baray, J.-L., Mas, T., Deguillaume, L., Ervens, B., and Amato, P.: Partitioning of microbial cells between clouds and precipitation , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2876, https://doi.org/10.5194/egusphere-egu2020-2876, 2020.

Delhi, the capital city of India with more than 10 million population, is suffering one of the worst particulate matter (or PM2.5) pollution over the world. Based on continuous observations during 2015-2018, we report that the PM2.5 pollution in Delhi is possibly one of the worst within Indian cities, and responsible for ~10,000 premature deaths of cities per year. Especially during the Diwali Fest, the hourly PM2.5 concentrations went above 1600 ug/m³, leading to ~20 extra premature deaths per day (Chen et al., 2019). We find a distinct seasonal variation of PM2.5 mass concentrations and a shift of morning rush hour from winter to summer, but a negligible weekend effect in Delhi. We also report a long-term result of hygroscopicity of PM2.5 in Delhi is about κ= 0.42 ± 0.07 for the first time, indicating much higher potential of cloud droplet activation from fine particles in Delhi compared with other Asian megacities, such as Beijing (κ=0.14–0.23) (Wang and Chen, 2019). It means, in addition to the great health burden, more significant cloud activation and greater influences on climate and hydrologic cycle are expected from fine particles in Delhi.

Method & Data

             We analysed the PM2.5 observations from US Embassy in Delhi, and used the Integrated Exposure Response Function to estimate the long-term and short-term health effect of PM2.5 exposure with a particular focus on the Diwali Fest period. Together with the temperature, RH and visibility data from the DEL airport in Delhi, we retrieved the 2016-2018 averaged hygroscopicity (κ) in Delhi according to the κ-kÓ§hler and Mie theories. In summary, we firstly retrieve the optical enhancement from visibility and RH, and then retrieve the optical-κ, and finally estimate the κ from the optical-κ. The detailed retrieving method is given in Wang and Chen (2019), this method has been validated in Beijing within an uncertainty of 30%.

Summary

                Our results show a strong seasonal variation of PM2.5 in Delhi, with severest pollution during the winter. The Diwali and New Year Fests also lead to extreme pollution events, i.e. worse than the ‘Severe’ Level, in the beginning of November and January. These lead to adverse health effect and make Delhi the top-1 health burden city in India. The long-term averaged hygroscopicity of PM2.5 in Delhi is much higher than Beijing and Asian average. This indicate much easier for fine particles serving as cloud condensation nuclei and contributing the climate change and hydrology cycle. Moreover, the high optical enhance factor, f(RH), implies strong direct radiative forcing enhancement and influences on the heterogeneous reactions in Delhi.

Acknowledgement: We thank NERC Fund supported project (NE/P01531X/1) and the joint scholarship of China Scholarship Council and University of Manchester. We thank the U.S. National Climatic Data Center and AirNow platform maintained by the EPA provide the observations.

References:

Chen, Y., Wild, O., Conibear, L., Ran, L., He, J., Wang, L., and Wang, Y.: Atmospheric Environment: X, 100052, 10.1016/j.aeaoa.2019.100052, 2019.

Wang, Y., and Chen, Y.: Geophysical Research Letters, 10.1029/2019GL082339, 2019.

How to cite: Chen, Y., Conibear, L., Wang, Y., Ran, L., He, J., Wang, L., and Wild, O.: Air Pollution and its potential climate effect in Delhi, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-223, https://doi.org/10.5194/egusphere-egu2020-223, 2020.

In recent years, China's industrialization and urbanization have accelerated, generating high emissions of pollutants every year, which has significantly deteriorated the air quality of Chinese cities and threatened public health and the happiness of urban residents. More and more studies have shown that several megacities in China and more and more cities have experienced more severe smog pollution. The occurrence of haze seriously affects the healthy development of human beings, so the research on haze should be vigorously promoted. Although many studies have made considerable progress in the research of smog in recent years, there is no systematic and comprehensive assessment method. But scholars have not stopped the pace of research.This study takes Weinan City, Shaanxi, China as the research object, The paper describes the formation mechanism of haze and the combined effects of emission sources, chemical aerosol material formation and transformation, meteorology and climatic conditions. The mechanism of haze formation is relatively complicated. Aerosols are widely used in the research of haze composition.Organic aerosols have a very important impact on the Earth's radiation, visibility and air quality on a global scale. However, the formation of secondary pollution makes this process more complicated. Secondary organic aerosols (SOA), free radicals that form volatile organic compounds and particles with ozone (O3), hydroxyl (OH) and nitrate (NO3) and artificial volatile organic compounds (VOCs) are considered organic gases One of the most important components of sol. In the past few decades, many studies have been conducted to study the formation of SOA. However, due to the complex formation mechanism of SOA, no further reason has been clarified.The reasons for the formation of haze are more complicated. For the true solution of the haze problem is still the key for our scholars to solve in the future, the government should also formulate corresponding measures to reduce the early discharge of pollutants, control the haze from the source, in short A long way to go requires joint efforts from everyone.

Keywords:Haze  Aerosol  Meteorological conditions  Weinan

How to cite: Meng, Y., Xi, J., and Wang, Y.: Discussion on the formation mechanism of severe haze in North China and its relationship with meteorological factors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4343, https://doi.org/10.5194/egusphere-egu2020-4343, 2020.

Organic aerosol (OA) constitutes a significant fraction of the atmospheric fine particulate matter that influences both air quality and climate. Secondary organic aerosol (SOA), which is formed through photo-oxidation of organic vapors in the atmosphere, is a major component of OA. There are some studies indicating the major role of Chinese cooking emissions in SOA formation in China. However, SOA formation is complex and uncertain.

In this study, we investigate the primary emission and secondary formation from Chinese cooking. The cooking ways include stir-fry, fry, and deep fry. The dishes were stir-fired shredded cabbage, fried Tofu, Kung Pao Chicken, and fired Chicken. Besides, different kinds of oils were fried to investigate the effect of oil on emission. The cooking emission was diluted and exposed a range concentration of oxidants (O₃ and OH) in the Go-PAM. Two SMPS were used to measure particle number concentrations before and after oxidation. A DMA-CPMA-CPC system was used to obtain the size resolved particle density, and together with particle number concentration, primary and secondary particle mass concentrations were calculated. One ptr-MS was used to measure primary VOCs concentration, and one Aerodyne VOCUS was deployed to measure the VOCs after PAM. An AMS was used to measure the secondary particles. Our results showed that the SOA/POA ratios varied significantly from 5-35, depending on cooking ways. The emission stir-fired shredded cabbage has largest SOA/POA ratio of 35, followed by fried Tofu (22), Kung Pao Chicken (16), and fried chicken (5). The O:C ratio increased from 0.12~0.26 of cooking POA to 0.40~0.52 of cooking SOA. Our results suggest Chinese cooking contributes significantly to ambient not only primary particles but secondary particles.

How to cite: Guo, S., Wang, H., Zhu, W., Zhang, Z., Chen, Z., Tang, R., Shen, R., Wang, T., Yu, Y., Tan, R., and Hu, M.: Secondary Organic Aerosol Formation from Chinese Cooking Emission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7246, https://doi.org/10.5194/egusphere-egu2020-7246, 2020.

Fine particulate matter (PM_2.5), which consists of solid and liquid particles and mixture of both suspended in the near surface atmosphere, is known to be one of the most threatening elements to human health by penetrating skin, lungs and bronchi. There have been diverse studies with regard to monitoring near-surface PM_2.5, particularly over East Asia, where recent rapid industrial development has produced serious air pollution. Some countries have already been operating ground-based monitoring networks and collecting relevant data. However, due to their poor spatial representativeness and inhomogeneous data quality, many of the previous studies were conducted based on space-borne observations. In this study, we tried to monitor concentrations of PM_2.5, particles with aerodynamic diameters less than 2.5 µm, based on GOCI top of atmosphere reflectance using a deep neural network (DNN) method. DNN is a kind of machine learning developed from artificial neural networks. In order to enhance the model performance, near-surface atmospheric information from Unified Model was also used as input variables such as surface temperature, dew point temperature, surface pressure, height of planetary boundary layer, relative humidity and wind fields. Sensitivity examinations were conducted to find optimal structures of training models and several techniques (e.g., regularization, early stopping, and normalization of input variables) were applied to prevent over-fitting training datasets. The retrieved data were characterized by comparing with estimates from the operational MCAQ model, which is used in air quality forecasting, and conventional linear regression results.

How to cite: Lee, C. S., Kim, S.-M., Lee, K.-H., Yoon, J., Hong, H., Choi, W. J., and Lee, D.-W.: Estimation of ground PM2.5 based on GOCI TOA reflectance using Deep Neural Network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6390, https://doi.org/10.5194/egusphere-egu2020-6390, 2020.

Particulate matter (PM) affects visibility and climate through light scattering, direct and indirect radiative forcing, and affecting cloud formation [1]. In addition, exposure to ambient fine PM is estimated to have caused 8.9 million deaths worldwide in 2015 [2]. Organic matter (OM), can make up more than half of total fine atmospheric PM, and yet its composition, formation mechanisms, and adverse health effects are not fully characterized due to its sheer compositional complexity. Biomass burning (e.g., residential wood burning, wildfires, and prescribed burning) and coal combustion (for heat and power generation) are two major OM sources, for which the impact of atmospheric aging - including secondary organic aerosol (SOA) formation - is not yet fully clear [3].

In this study, we investigated the effect of aging on composition and mass concentration of organic aerosols of wood burning (WB) and coal combustion (CC) emissions using two complementary methods, i.e., mid-infrared spectroscopy and aerosol mass spectrometry (AMS). For this purpose, primary aerosols were injected into the Paul Scherrer Institute (PSI) environmental chamber and aged using hydroxyl and nitrate radicals to simulate day-time and night-time oxidation processes in the atmosphere. In these experiments, aerosols reached an oxidative age comparable to that of atmospheric aerosols. A time-of-flight AMS instrument was used to measure the high-time-resolution composition of non-refractory fine PM, while we collected PM₁ aerosols on PTFE filters before and after four hours of aging for off-line Fourier transform-infrared spectroscopy (FT-IR) measurements.

AMS and FT-IR estimates of organic aerosol mass concentration were highly correlated (r²=0.92); both indicating an approximately three-fold increase in organic aerosol concentration after aging. The OM/OC ratio, indicating the extent of oxidation also agreed closely between the two instruments and increased, on average, from 1.6 (before aging) to 2 (after aging). Mid-infrared spectroscopy, which is able to differentiate among oxygenated species, shows a distinct functional group composition for aged WB aerosols (high abundance of carboxylic acids) and CC aerosols (high abundance of non-acid carbonyls) and detects considerable amounts polycyclic aromatic hydrocarbons (PAHs) for both sources. Mid-infrared spectra of fresh WB and CC aerosols are reminiscent of their parent compounds with differences in specific functional groups suggesting the dominant oxidation pathways for each emission source. Finally, the comparison of mid-infrared spectra of aged WB aerosols in the environmental chamber with that of ambient samples affected by residential wood burning and wildfires reveals interesting similarities regarding the high abundance of alcohols and visible signatures of lignin. This finding is useful for interpreting sources of atmospheric aerosols and better interpretation of their complex mid-infrared spectra.

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REFERENCES

[1] M. Hallquist et al., “The formation, properties and impact of secondary organic aerosol: current and emerging issues,” Atmos Chem Phys, 2009.

[2] R. Burnett et al., “Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter,” Proc. Natl. Acad. Sci., 2018.

[3] A. Bertrand et al., “Primary emissions and secondary aerosol production potential from woodstoves for residential heating: Influence of the stove technology and combustion efficiency,” Atmos. Environ., 2017.

How to cite: Yazdani, A., Dudani, N., Takahama, S., Bertrand, A., Prévôt, A. S. H., El Haddad, I., and Dillner, A. M.: Organic functional group composition of particulate matter from fresh and aged wood burning and coal combustion , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5313, https://doi.org/10.5194/egusphere-egu2020-5313, 2020.

Oxidized organic aerosol (OOA) is a major component of ambient particulate matter, substantially affecting both climate and human health. A considerable body of evidence has established that OOA is readily produced in the presence of daylight, thus leading to the association of high concentrations of OOA in the summer or mid-afternoon. However, this current mechanistic understanding fails to explain elevated OOA concentrations during night or wintertime periods of low photochemical activity, thus leading atmospheric models to under predict OOA concentrations by a factor of 3-5. Here we show that fresh emissions from biomass burning rapidly forms OOA in the laboratory over a few hours and without any sunlight. The resulting OOA chemical composition is consistent with the observed OOA in field studies in major urban areas. To estimate the contribution of nocturnally aged OOA in the ambient atmosphere, we incorporate this nighttime-aging mechanism into a chemical-transport model and find that over much of the United States greater than 75% of the OOA formed from fresh biomass burning emissions underwent nighttime aging processes. Thus, the conceptual framework that OOA is predominantly formed in the presence of daylight fails to account for a substantial and rapid oxidation process occurring in the dark.

How to cite: Kodros, J., Papanastasiou, D., Paglione, M., Masiol, M., Squizzato, S., Florou, K., Kołodziejczyk, A., Skyllakou, K., Nenes, A., and Pandis, S.: The oxidizing power of the dark side: Rapid nocturnal aging of biomass burning as an overlooked source of oxidized organic aerosol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7382, https://doi.org/10.5194/egusphere-egu2020-7382, 2020.

Recent laboratory studies have reported the formation of light-absorbing organic carbon compounds (brown carbon, BrC) in aqueous particles undergoing drying.  Atmospheric particles undergo cycles of humidification and drying during vertical transport and through daily variations in temperature and humidity, which implies particle drying could potentially be an important source of BrC globally.  In this work, we investigated BrC formation in ambient particles undergoing drying at a site in the eastern United States during summer.  Aerosol BrC concentrations were linked to secondary organic aerosol (SOA) formation, consistent with seasonal expectations for this region.  Measurements of water-soluble organic aerosol concentrations and light absorption (365 nm) were alternated between an unperturbed channel and a channel that dried particles to 41% or 35% relative humidity (RH), depending on the system configuration. The RH maintained in the dry channels was below most ambient RH levels observed throughout the study.  We did not observe BrC formation in particles that were dried to either RH level. The results were consistent across two summers, spanning ~5 weeks of measurements that included a wide range of RH conditions and organic and inorganic aerosol loadings.  This work suggests that mechanisms aside from humidification-drying cycles are more important contributors to ambient particle BrC loadings.  The implications of this work on the atmospheric budget of BrC are discussed.

How to cite: Pratap, V., Battaglia Jr., M., Carlton, A., and Hennigan, C.: No Evidence for Brown Carbon Formation in Ambient Particles Undergoing Atmospherically Relevant Drying, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3669, https://doi.org/10.5194/egusphere-egu2020-3669, 2020.

Nitrogen molecules are present in the atmosphere also as inorganic ions (ammonium, nitrate…) and organic (peptides and proteins). Nowadays, there is still poor knowledge concerning the sources and fate of proteins and peptides in the atmosphere. In a larger context aiming at exploring microbial communities’ functioning in the atmosphere, the goal of this study is to examine the atmospheric proteome (peptide and protein contents, sequence, size distribution, biological functions) in the different atmospheric compartment (aerosols, cloud and rain waters).

Aerosols, cloud water and rain samples were collected at remote places nearby Clermont – Ferrand city (France) and from the Mountain “Puy de Dôme” (1465 m asl). Cloud droplet impactors and high volume impingers were used for allowing immediate fixation of the samples, by collecting within a protease inhibitor solution. Samples were filtered (0.22 µm porosity) and the proteins from water were digested using trypsin. The peptides were purified by solid phase extraction (SPE) method, concentrated by lyophilisation and analysed by LC – HRMS and MS². Preliminary results indicate the recurrence of certain small peptides in particular. Some of these most frequently observed peptides were selected as models for photochemical experiments. Briefly, these small peptides were irradiated under solar simulated conditions and products were identified by IC – MS, to assess the impact of such processes on the chemical composition of the atmosphere.

The next step will consist in analysing our observations along with chemical and biological parameters such as biodiversity, transcriptomic profiles, in order to better understand the interaction between microorganisms and atmosphere processes.

How to cite: Ghaffar, C., Brissy, M., Dieme, B., Lerembourg, M., Brigante, M., and Amato, P.: Study of nitrogen compounds in different atmospheric compartments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13217, https://doi.org/10.5194/egusphere-egu2020-13217, 2020.

Here we show recent results from different field and laboratory campaigns focusing on organonitrate (ON) formation, mass concentration, and physicochemical properties such as volatility. ONs are formed via volatile organic compounds (VOC) and NO_x. They are therefore key species for our understanding of the interaction between the biosphere and anthropogenic activities, and the effects of altering both VOC and NO_x emissions due to climate change and/or air quality mitigation measures. Recently, we were able to show that ONs from different precursor VOC can also contribute significantly to the growth of newly formed particles in the atmosphere to sizes where they can become active and cloud condensation nuclei (Huang et al., 2019).

We present direct, real-time observations of ONs in the gas and particle phase at the highest atmospheric research station in the world, Chacaltaya (5240 m a. s. l) in Bolivia. This southern hemisphere station is often located in the free troposphere during night time, and influenced by the emissions from the nearby El Alto-La Paz metropolitan area, and biogenic emissions from surrounding forests as well as from the Amazon through long-range transport. ONs were measured using a Chemical Ionization Mass Spectrometer with a Filter Inlet for Gases and Aerosols. We observed hundreds of highly functionalized ONs with different molecular composition during day- and nighttime, indicating different sources and formation processes. A large contribution of the highly functionalized ONs was found especially during new particle formation events regularly observed at this location (Rose et al., 2015). Observations from the field will be compared to results from the Nitrate Aerosol and Volatility Experiment (NArVE) at the EUROCHAMP 2020 PACS-C3 smog chamber (PSI, Switzerland), where we investigated the ON fraction, chemical composition, and volatility of secondary organic aerosol (SOA) formed via nitrate radical initiated oxidation reactions of biogenic and anthropogenic VOC.

How to cite: Mohr, C., Wu, C., Huang, W., Graham, E., Bianchi, F., Andrade, M., and Bell, D.: Molecular characterization and volatility of organonitrates: Latest observations from field and laboratory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19552, https://doi.org/10.5194/egusphere-egu2020-19552, 2020.

The chemistry of organic nitrates (ONs), also known as alkyl nitrates (RONO₂), controls the lifetime of nitrogen oxides in continental areas, which in turn affects air quality and varies ozone concentration throughout the troposphere. ONs can be emitted to the troposphere from marine sources. Also, they can be produced in the atmosphere through addition of NO to peroxy radicals or through the reaction of NO₃ radicals with volatile organic compounds. Atmospheric ONs may subsequently undergo oxidation or photolysis, in both gas and aerosol phases, or hydrolysis in aqueous aerosols. Though some recent studies have believed acid-catalysis promotes hydrolysis of ONs, earlier studies have claimed that acids have no effect on ON hydrolysis, and that it is the hydroxyl ion that can improve the hydrolysis process. The limited number of experimental studies performed so far have left this conflict with no appropriate answer, as mechanistic insight and full kinetics details have been partially or completely missing for the studied ONs. We report the detailed mechanism of methyl nitrate hydrolysis in acidic, neutral and basic conditions, in addition to analyzing the degradation of methyl nitrate into formaldehyde and nitrous acid in the presence of water and hydronium ions. According to the potential energy surfaces obtained at the CCSD(T)/cc-pVDZ//ωB97X-D/def2-TZVP level of theory (including the SMD solvent model) along with the rate coefficients estimated using asymmetric Eckart tunneling-corrected transition state theory (TST), mediation of water molecules and hydronium ions hinders degradation of methyl nitrate into formaldehyde and nitrous acid and, in general, this decomposition reaction is kinetically unfavorable. Furthermore, neutral hydrolysis of methyl nitrate is extremely slow with pseudo-first order rate coefficients (k; 298 K and 1 atm) falling below 10^-27 s^-1. Similarly, hydrolysis of methyl nitrate by hydronium ions is observed to be extremely slow (k < 10^-27 s^-1). However, under acidic conditions, protonation of methyl nitrate is quite feasible with the protonation Gibbs free energy of -429.1 kJ mol^-1, at 298 K and 1 atm, and protonated methyl nitrate can hydrolyze into protonated methanol and nitric acid much faster relative to the hydronium ion-based and neutral hydrolysis (k = 3.83 s^-1). On the other hand, the hydroxyl ions generated under basic conditions can hydrolyze methyl nitrate readily to give methanol and nitric acid (k = 6.63 × 10³ s^-1), or formaldehyde, nitrate and water (k = 9.40 × 10⁶ s^-1). In addition, regardless of the limitation on the rate of solvent-phase chemical reactions by the rate of diffusion, basic hydrolysis can produce methoxy ions and nitric acid quite fast (k = 8.95 × 10⁹ s^-1). In other words, methyl nitrate hydrolysis is faster in basic aerosols (i.e. some marine aerosols) and, to a less extent, in highly acidic aqueous aerosols (e.g. haze and urban aerosols).       

How to cite: Keshavarz, F., Kurtén, T., and Vehkamäki, H.: Basicity and acidity promote hydrolysis of methyl nitrate in aqueous aerosols, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3530, https://doi.org/10.5194/egusphere-egu2020-3530, 2020.

Sulfur and nitrogen containing organic compounds, such as organosulfates (OSs) and nitrooxy organosulfates (NOSs), are recognized to be ubiquitously present in secondary organic aerosol (SOA). However, little is known about the chemical mechanisms or the required conditions for the formation of these compounds in the ambient atmosphere. Earlier studies have commonly suggested that OSs are predominantly formed through the reaction of organic gaseous epoxides with acidic sulfate particles. However, this epoxide pathway often fails to explain the formation of (N)OSs from monoterpenes. Moreover, recent studies highlight the potential role of gas-phase SO₂ and organic peroxides for the formation of OSs, which might serve as predominant precursors for OSs and NOSs from atmospheric monoterpene oxidation.

Here, we conducted a series of chamber experiments to elucidate the formation mechanisms of (N)OSs from α-pinene oxidation during daytime and nighttime conditions. In particular, we focused on the role of organic peroxides and S(IV) (i.e., gas-phase SO₂ and particulate SO₃^2–) in contrast to organic epoxides and isotope-labelled particulate sulfate (i.e., S(VI)). SOA particles were analyzed online by extractive electrospray ionization coupled with high-resolution Orbitrap mass spectrometry (EESI-Orbitrap MS) allowing an unambiguous identification of OS and NOS species with a high time resolution. Additionally, filter samples were collected and analyzed by liquid chromatography (LC) coupled with Orbitrap MS to determine the presence of isomeric compounds.

Consistently, online and offline Orbitrap MS analysis showed that particulate sulfate played a minor role in the formation of OSs and NOSs. In contrast, (N)OSs were rapidly formed upon addition of either gaseous SO₂ or particulate SO₃^2–, suggesting S(IV) to react with organic peroxides that were formed through monoterpene oxidation. Based on these experiments, we identified specific NOS species that are formed only through either daytime or nighttime chemistry, and thus, might serve as marker molecules. Moreover, we present complete formation pathways for these species. Our study indicates that in contrast to previous work, the formation of OSs and NOSs does not require acidic sulfate particles, but rather involves the reaction of organic peroxides with S(IV) in the gas phase or the particle phase.

How to cite: Brüggemann, M., Riva, M., Dubois, C., Mutzel, A., George, C., and Herrmann, H.: Formation of (nitrooxy)organosulfates from organic peroxides and S(IV) via daytime and nighttime chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13355, https://doi.org/10.5194/egusphere-egu2020-13355, 2020.

Deeper understanding of the behaviour of aerosol particles in the atmosphere is essential for the continued improvement of aerosol representation within models. The saturation vapour pressure (P^sat ) of secondary organic aerosols (SOA) can be used to predict partitioning between the gaseous and particulate phase. The extent of this partitioning affects the behaviour of SOA in the atmosphere¹.

Typically P^sat  of SOA are estimated using group contribution methods (GCMs) due to a lack of experimental data. The reliability of GCMs, when applied to a certain compound, depend on the how well represented the functionality present in the compound of interest is represented in the fitting data set of the GCM².

Nitroaromatics are a class of compound that are useful atmospheric tracers for anthropogenic emissions³, and many nitroaromatic compounds are noted to be toxic⁴. There is a lack of atmospherically relevant experimental data available for nitroaromatic compounds. This leads to poor performance of GCMs when they try and predict P^sat . Additional experimentally determined P^sat data can be used to expand the fitting data sets of GCMs allowing for more accurate prediction in the future.

In this study we present results from recent experiments using Knudsen Effusion Mass Spectrometry (KEMS) and differential scanning calorimetry (DSC) and compare these results with predicted values from multiple GCMs. The KEMS measurements are supported by additional data from diffusion controlled evaporation rates of single particles in an electrodynamic balance (EDB). In many cases the differences between the experimental data and the predicted values was several orders of magnitude. The limited nitroaromatic data within the GCM fitting sets are then investigated so that the mostly likely causes of the multiple order of magnitude differences between the predicted values and experimental values can be identified.

1         M. Bilde, K. Barsanti, M. Booth, C. D. Cappa, N. M. Donahue, E. U. Emanuelsson, G. McFiggans, U. K. Krieger, C. Marcolli, D. Topping, P. Ziemann, M. Barley, S. Clegg, B. Dennis-Smither, M. Hallquist, Å. M. Hallquist, A. Khlystov, M. Kulmala, D. Mogensen, C. J. Percival, F. Pope, J. P. Reid, M. A. V Ribeiro da Silva, T. Rosenoern, K. Salo, V. Pia Soonsin, T. Yli-Juuti, N. L. Prisle, J. Pagels, J. Rarey, A. A. Zardini and I. Riipinen, Chem. Rev, 2015, 115, 4115–4156.

2         T. Kurtén, K. Tiusanen, P. Roldin, M. Rissanen, J.-N. Luy, M. Boy, M. Ehn and N. Donahue, J. Phys. Chem. A, 2016, 120, 2569–2582.

3         D. Grosjean, Atmos. Environ. Part A. Gen. Top., 1992, 26, 953–963.

4         P. Kovacic and R. Somanathan, J. Appl. Toxicol., 2014, 34, 810–824.

How to cite: Shelley, P., Bannan, T., Worrall, S., Krieger, U., Alfarra, M. R., and Topping, D.: Investigating the Vapour Pressures of Nitroaromatic Compounds Using Knudsen Effusion Mass Spectrometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5370, https://doi.org/10.5194/egusphere-egu2020-5370, 2020.

Biogenic secondary organic aerosol (SOA) is formed as a result of the atmospheric oxidation of gas-phase biogenic volatile organic compounds (BVOCs). Here, we evaluate the ability of five European Earth System Models (CNRM-ESM2-1, EC-Earth3, IPSL-CM6, NorESM1.2, UKESM1) to capture the amount, and behaviour, of biogenic SOA in the atmosphere.

The ESMs cover a range of complexity in terms of their representation of the sources and processing of biogenic SOA (i.e., from a fixed climatology of SOA amount to an interactive BVOC emission scheme followed by atmospheric processing).

We combine station measurements of BVOC emission and atmospheric BVOC concentrations with remotely sensed isoprene emission estimates to evaluate the models’ representation of the sources of biogenic SOA. We use organic aerosol mass and particle number concentration measurements from a number of forested sites to evaluate the ability of the models to capture the seasonal cycle in the amount of biogenic SOA present, as well as its impact on the aerosol size distribution. Whilst the models appear to capture the seasonal cycle in organic aerosol well for a boreal forest site, the ESMs consistently over-predict the amount of organic aerosol present at a tropical forest location. 

Finally, we explore the ability of these models to capture the observed relationships between organic aerosol mass, or particle number, and temperature. We find that the ESMs equipped with vegetation models that generate BVOC emissions interactively are able to capture well the strength of the observed relationship between temperature and organic aerosol mass. This lends confidence to the ability of these ESMs to accurately represent changes in atmospheric composition driven by climate.

How to cite: Scott, C., Yoshioka, M., Dearden, C., Carslaw, K., Spracklen, D., O'Connor, F., Folberth, G., Dalvi, M., Mulcahy, J., Balkanski, Y., Checa-Garcia, R., Olivie, D., Schulz, M., van Noije, T., le Sager, P., Michou, M., Nabat, P., Nieradzik, L., Bergman, T., and O'Donnell, D.: How well do the latest Earth System Models capture the behaviour of biogenic secondary organic aerosol in the atmosphere?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16195, https://doi.org/10.5194/egusphere-egu2020-16195, 2020.

Aerosol optical properties, such as particle light scattering, depend on the particle size and chemical composition, which in turn are affected by the particle’s ability to take up water. Thus, particle hygroscopic growth will have an impact on the optical properties and in turn will affect the aerosol-radiation interaction and the calculations of the Earth’s radiative balance. The dependence of particle light scattering on relative humidity (RH) can be described by the scattering enhancement factor f(RH), defined as the ratio between the particle light scattering coefficient at a given RH divided by its dry value.

In our previous work (Burgos et al., 2019), we carried out a standardized analysis of scattering in-situ measurements at 26 sites around the globe, creating a benchmark dataset (open access via EBAS, http://ebas.nilu.no/). The project continues with the present work, which is part of the AeroCom phase III INSITU project: Evaluation of hygroscopicity of aerosol optical properties. Here, we present a comprehensive model-measurement evaluation of f(RH) for ten different earth system models. Modelled and measured scattering enhancement factors are compared for 22 sites, representative of Arctic, marine, rural, mountain, urban and desert aerosols.

Overall, a large variability and diversity in the magnitude of predicted f(RH) amongst the models is found and the modelled f(RH) tends to be overestimated relative to the measurement values. This difference cannot be explained by the aerosol type. Agreement between models and measurements was strongly influenced by the choice of RH_ref. Models show a significantly larger discrepancy with the observations if model dry conditions are set to RH=0% instead of RH=40%. Model parameterizations of aerosol hygroscopicity and mixing state may be driving the observed diversity among models as well as the discrepancy with measurements. Measurement conditions have to be considered in this type of evaluation, specifically the fact that “dry” measurements may not be “dry” in model terms.

This work has been submitted to ACPD.

Burgos, M., Andrews, E., Titos, G., Alados-Arboledas, L., Baltensperger, U., Day, D., Jefferson, A., Kalivitis, N., Mihalopoulos, N., Sherman, J., Sun, J., Weingartner, E., and Zieger, P.: A global view on the effect of water uptake on aerosol particle light scattering, Scientific Data, 6, https://doi.org/10.1038/s41597-019-0158-7, 2019.

How to cite: Burgos Simón, M. Á. and the Aerosol hygroscopicity - model evaluation team: First global evaluation of the representation of water uptake within ten earth system models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18027, https://doi.org/10.5194/egusphere-egu2020-18027, 2020.

Atmospheric aerosols are evolving mixtures of different chemical species.  The term “aerosol mixing state” is commonly used to describe how different chemical species are distributed throughout a particle population.  A population is “fully internally mixed” if each individual particle consists of same species mixtures, whereas it is fully externally mixed if each particle only contains one species. Mixing state matters for aerosol health impacts and for climate-relevant aerosol properties, such as the particles’ propensity to form cloud droplets or the aerosol optical properties.

The mixing state metric χ quantifies the degree of internal or external mixing and can be calculated based on the particles’ species mass fractions. Several field studies have used this metric to quantify mixing states for different ambient environments using sophisticated single-particle measurement techniques. Inherent to these methods is a finite number of particles, ranging from a few hundred to several thousand particles, used to estimate the mixing state metric. 

This study evaluates the error that is introduced in calculating χ due to a limited particle sample size.  We used the particle-resolved model PartMC-MOSAIC to generate a scenario library that encompasses a large number of reference particle populations and that represents a wide range of mixing states. We stochastically sub-sampled these particle populations using sample sizes of 10 to 10,000 particles and recalculated χ based on the sub-samples. This procedure mimics the impact of only having a limited sample size as it is common in real-world applications. The finite sample size leads to a consistent overestimation of χ, meaning that the populations appear more internally mixed than they are in reality. These findings are experimentally confirmed using single-particle SP-AMS measurement data from the Pittsburgh area. We also determined confidence intervals of χ for our sub-sampled populations. To determine χ within a range of  +/- 10 percentage points requires a sample size of at least 1000 particles.

How to cite: Riemer, N., Gasparik, J., Ye, Q., West, M., Curtis, J., Sullivan, R., and Presto, A.: How many particles do we need to measure aerosol mixing state?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6132, https://doi.org/10.5194/egusphere-egu2020-6132, 2020.

The recently introduced PTR3-TOF mass spectrometer (Proton Transfer Reaction Time-Of-Flight) allows for a direct and quantitative detection of volatile organic compounds (VOC) and their oxidation products. With a design of the inlet system and the ionization chamber that allows analyte transfer with virtually no wall interactions, organics ranging from volatile to extremely low volatility (ELVOC) can be measured, even at ambient temperature. In addition, PTR3 has recently shown to detect and quantify RO₂ radicals. Unlike the traditional PTR-MS ionization technique, the PTR3 is operated at an elevated reaction pressure of 50 to 80 mbar while reaction kinetics are precisely defined via radial electric fields emitted from a tripole ion guide. With this setup, outstanding sensitivities of more than 30,000 cps/ppbV are achieved.

Herein, we present an improved version of a PTR3-TOF instrument. The inlet comprises three cylindrically arranged ion sources allowing for fast electrical switching between a set of reagent ions including H₃O⁺, NO⁺, O₂⁺ and NH₄⁺. The tripole geometry is aerodynamically improved to further reduce surface interactions. Extraction of analyte ions from the PTR3 ionization chamber and subsequent transfer to the TOF mass analyzer is now enhanced by an ion booster in series to a hexapole ion guide. This setup enables a precise control of extraction energies to reduce unwanted collision induced fragmentation and at the same time efficiently transmits ions of a broad m/z range. Analyte ions are analyzed with a high-resolution Time-Of-Flight mass spectrometer achieving mass resolving powers of typically 13,000 to 15,000.

We have characterized the performance of this optimized PTR3-TOF instrument using pure chemical compounds of intermediate to low volatility, including carboxylic acids and peroxides. Hereby, the effects of PTR3 reaction conditions and ion extraction settings are studied. Monoterpene ozonolysis experiments demonstrate the performance in detecting aerosol precursors from intermediate to extremely low volatility. These new insights in gas phase chemistry are further combined with particle phase measurements conducted with a CHARON PTR-MS to emphasize the analytical capabilities of the PTR3.

How to cite: Leiminger, M. S., Reinecke, T., Müller, M., Feil, S., Sulzer, P., and Jordan, A.: Characterization of an improved PTR3 mass spectrometer for the detection of highly oxidized aerosol precursors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18016, https://doi.org/10.5194/egusphere-egu2020-18016, 2020.

We have shown in previous work that Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS) in combination with the “Chemical Analysis of Aerosol Online" (CHARON) inlet is a powerful tool for direct and online analysis of sub-µm particulate organic matter in the urban atmosphere. Herein, we report on the first CHARON PTR-ToF-MS measurements in the continental background environment, at the TROPOS Research Station in Melpitz near Leipzig (Germany) during a three week period in February 2019.

A state-of-the-art CHARON PTR-TOF 6000X2 instrument (IONICON Analytik GmbH, Austria) was used for measuring particulate organic compounds online (i.e., without filter pre-collection) and in real-time (< 1-min time resolution), at sub-ng m^-3 mass concentrations, and on an elementary composition level. Periodic switching between the standard PTR-MS gas-phase inlet and the CHARON particle inlet made it possible to comprehensively measure atmospheric organic matter in both the gaseous and particulate state at a time resolution of 10 minutes. In addition, an aerosol mass spectrometer (HR-TOF-AMS) and an aerosol chemical speciation monitor (ACSM; both Aerodyne Inc., USA) were deployed for monitoring the composition of non-refractory particulate matter. A Dual Mobility Particle Size Spectrometer (TROPOS-type T-MPSS) was used for determining the total particle size distribution. In addition, particles were collected on filters once per day and analysed offline in the laboratory.

The CHARON PTR-TOF 6000X2 instrument operated stably and reliably over the three week measurement period. Our data show that a single instrument can be used for characterizing both gaseous and particle-bound organic matter in the atmosphere at 10 minute time resolution. The obtained data agree well with ACSM, HR-TOF-AMS and T-MPSS results. A comparison with the offline results obtained from the filter samples confirmed that the CHARON PTR-ToF-MS technique accurately measures the atmospheric concentrations of selected anhydrosugars and polycyclic aromatic hydrocarbons (PAHs). We also show that CHARON PTR-ToF-MS data are useful for improving the source apportionment of particles via positive matrix factorization (PMF).

This work is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654109 (ACTRIS-2). F. P. has received funding through the EU's Horizon 2020 programme under grant agreement Nº674911 (IMPACT). 

How to cite: Wisthaler, A., Müller, M., Poulain, L., Piel, F., Gräfe, R., Spindler, G., Wiedensohler, A., and Herrmann, H.: Chemical Characterization of Particulate and Volatile Organic Compounds in the Rural Wintertime Atmosphere by CHARON PTR-ToF-MS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19635, https://doi.org/10.5194/egusphere-egu2020-19635, 2020.

Oxidized and highly oxidized organic molecules are important target analytes in atmospheric air samples. In recent years, several chemical ionization mass spectrometry (CIMS) methods have been developed for detecting these target analytes in real time and at ultra-trace levels. One of these CIMS techniques is proton-transfer-reaction mass spectrometry (PTR-MS), which, in combination with the so-called CHARON inlet, measures oxidized and highly oxidized organic molecules in the atmosphere in the gaseous and particulate state. PTR-MS typically uses hydronium ions (H₃O⁺) as reagent ions for detecting organic analytes in their protonated form, [A+H⁺]. H₃O⁺ ions react with all oxidized organics at unit efficiency, meaning that PTR-MS universally detects these target analytes, with little dependency of the signal response on their oxidation state. A drawback of PTR-MS operation in the H₃O⁺ mode is that oxidized functional groups are often ejected upon protonation.

Herein, we present the results obtained when a CHARON PTR-MS analyzer was operated with ammonium (NH₄⁺) ions as CI reagent ions. We studied the instrumental response to a set of oxidized and highly oxidized compounds including hydroxy, carboxy and peroxy functional groups. We found that fragmentation was greatly suppressed, with ammonium adducts, [A+NH₄]⁺, being the main analyte ions formed. The ionization efficiency ranged from 10 to 80% of the collisional limit, meaning that the NH₄⁺ mode is less quantitative than the H₃O⁺ mode. The performance and advantages of ammonium adduct ionization are demonstrated on two application examples: i) secondary organic aerosol generated in the laboratory from the ozonolysis of limonene, with a particular focus on the detection of peroxides and dimers, and (ii) ambient organic aerosol in Innsbruck, Austria, which was characterized at the molecular level at single digit ng m^-³ mass concentrations.

How to cite: Müller, M., Piel, F., and Wisthaler, A.: On the detection of oxidized and highly oxidized organic molecules by CHARON PTR-MS via ammonium adduct ionization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4471, https://doi.org/10.5194/egusphere-egu2020-4471, 2020.

Atmospheric new particle formation (NPF) generates secondary aerosol particles into the lower atmosphere via gas-to-particle phase transition. Secondary aerosol particles dominate the total particle number concentration and are an important source for cloud condensation nuclei ^[1]. NPF typically begins with clustering among gaseous molecules. Once the newly formed clusters attain a size larger than the critical cluster size (~1.5 nm), their growth to larger sizes is energetically favoured and eventually they become nanoparticles ^[2]. NPF is often observed with the participation of air ions ^[3] and sometimes is induced by ions ^[4]. Air ions are a constituent of atmospheric electricity. The presence of the Earth-atmosphere electric field poses an electrical force on air ions. The earth-atmosphere electric field exhibits variability at different time scales under fair-weather conditions ^[5]. It is therefore interesting to understand whether the Earth-atmosphere electric field influences atmospheric new particle formation.

We analysed the Earth-atmosphere electric field together with the number size distribution data of air ions and aerosol particles under fair-weather conditions measured at Hyytiälä SMEAR II station in Southern Finland ^[6]. The electric field were measured by two Campbell CS 110 field mills in parallel. Air ion data were obtained with a Balance Scanning Mobility Analyser (BSMA) and a Neutral and Air Ion Spectrometer (NAIS), and aerosol particle data with a Differential Mobility Particle Sizer (DMPS). We used condensation Sinks (CS) derived from the DMPS measurement, air temperature, relative humidity, wind speed, global radiation as well as brightness derived from the global radiation measurement to assist the analysis. The measured earth-atmosphere electric field on NPF days was higher than on non-NPF days. We found that under low CS conditions, the electric field can enhance the formation of 1.7-3 nm air ions, but the concentration of 1.7-3 nm ions decreased with an increasing electric field under high CS conditions.

References:

[1]       Kerminen V.-M. et al., Environ. Res. Lett. 2018, 13, 103003.

[2]       Kulmala M. et al., Science 2013, 339, 943-946.

[3]       Manninen H. E. et al., Atmos. Chem. Phys. 2010, 10, 7907-7927.

[4]       Jokinen T. et al., Science Advances 2018, 4, eaat9744.

[5]       Bennett A. J., Harrison R. G., Journal of Physics: Conference Series 2008, 142, 012046.

[6]       Hari P., Kulmala M., Boreal Environ. Res. 2005, 10, 315-322.

How to cite: Chen, X., Barbosa, S., Mäkelä, A., Paatero, J., Monteiro, C., Guimarães, D., Junninen, H., Petäjä, T., and Kulmala, M.: The connection of atmospheric new particle formation to fair-weather Earth-atmosphere electric field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16571, https://doi.org/10.5194/egusphere-egu2020-16571, 2020.

Organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured with Sunset Laboratory Model-5 Semi-Continuous OC/EC Field Analyzer at Anmyeondo Global Atmosphere Watch (GAW) Regional Station (37°32´N, 127°19´E) in July and August, 2017. It employs TOT (Thermal-Optical-Transmittance) method. The mean values of OC and EC were 3.7 μg m^-3 and 0.7 μg m^-3, respectively. During the study period, the concentrations of reactive gases and aerosol species were evidently lower than those of other seasons. It is mostly due to meteorological setting of the northeast Asia, where the influence of continental outflow is at its minimum during this season under southwesterly wind. While the diurnal variation of OC and EC were not clear, the concentrations of O₃, CO, NOx, SO₂, and CO₂ were evidently enhanced under easterly wind at night from 20:00 to 8:00. However, the high concentration of EC was observed concurrently with CO and NOx under northerly wind during 20:00 ~ 24:00. It indicates the influence of thermal power plant and industrial facilities, which was recognized as a major emission source during KORUS-AQ campaign. The diurnal variation of O₃ clearly showed the influence of land-sea breeze, in which O₃ concentration was enhanced with OC in sea-breeze. OC concentration was relatively high, compared to those Seoul. This study suggests that in general, Anmyeondo station serves well as a background monitoring station. However, the variation in meteorological condition is so dynamic that it is primary factor to determine the concentrations of secondary species as well as primary pollutants at Anmyeondo station.

How to cite: Ham, J.: PM2.5 organic carbon (OC) and elemental carbon (EC) of summer monsoon season observed at the Anmyeondo Global Atmosphere Watch (GAW) Regional Station, South Korea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-946, https://doi.org/10.5194/egusphere-egu2020-946, 2020.

New particle formation (NPF) by gas-to-particle conversion occurs frequently in many different environments around the globe (Nieminen et al., 2018). NPF is the major contributor to the global cloud condensation nuclei budget (Gordon et al., 2017) and also impacts urban air quality (Guo et al., 2014). It is therefore crucial to understand how the newly formed particles can survive and grow to larger particles under different environmental conditions. Depending on the environment different condensable vapours and also different aerosol dynamics govern the NPF process.

In order to investigate the dynamics of aerosol growth in the sub-10 nm regime, where the newly formed particles are most vulnerable for losses to pre-existing aerosol, we tested several combining instrument inversion approaches. This allows to combine the measurements of several different particle sizing instruments in the sub-10 nm range, where each instrument offers different benefits and weaknesses. If the instruments are combined during the inversion, this could significantly reduce the error of the inferred particle size-distributions. Model results show that the regularization approach proposed by Wolfenbarger and Seinfeld (1990) yield the most stable inversion for data heavily influenced by measurement errors.

We than apply the tested inversion techniques to measurements in three different environments where an array of different state-of-the-art sub-10 nm sizing instruments was deployed: The SMEAR-II station in Hyytiälä, Finland, representative for a rural boreal forest background site, the SMEAR-III station in Helsinki, Finland, representative for a medium-polluted middle-scale European city, and at the Beijing University of Chemical Technology, China, an urban site in a global megacity.

We demonstrate that the combining instrument approach can enable a more detailed analysis of the cluster dynamics, e.g. by the application of size- and time resolving growth rate analysis tools (Pichelstorfer et al., 2018). This will lead to a better understanding of the role of coagulation and condensation in the particle growth process and will help to explain the different dynamics which lead to NPF in fundamentally different environments.

References:

Gordon, H. et al.: Causes and importance of new particle formation in the present-day and preindustrial atmospheres, J. Geophys. Res.-Atmos., 122, doi:10.1002/2017JD026844, 2017.

Guo, S. et al.: Elucidating severe urban haze formation in China, P. Nat. Acad. Sci. USA, 111(49), 17373 LP – 17378, doi:10.1073/pnas.1419604111, 2014.

Nieminen, T. et al.: Global analysis of continental boundary layer new particle formation based on long-term measurements, Atmos. Chem. Phys., (April), 1–34, doi:10.5194/acp-2018-304, 2018.

Pichelstorfer, L et al.: Resolving nanoparticle growth mechanisms from size- and time-dependent growth rate analysis, Atmos. Chem. Phys., 18(2), 1307–1323, doi:10.5194/acp-18-1307-2018, 2018.

Wolfenbarger, J. K. and Seinfeld, J. H.: Inversion of aerosol size distribution data, J. Aerosol Sci., 21(2), 227–247, doi:https://doi.org/10.1016/0021-8502(90)90007-K, 1990.

How to cite: Stolzenburg, D., Cai, R., Ahonen, L., Laurila, T., Holm, S., Kontkanen, J., and Kangasluoma, J.: Cluster dynamics in different environments: from the boreal forest to megacities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1700, https://doi.org/10.5194/egusphere-egu2020-1700, 2020.

Anthropogenic aerosol emissions have increased considerably over the last century, but climate effects and quantification of the emissions are highly uncertain as one goes back in time. This uncertainty is partly due to a lack of observations in the pre-satellite era, and previous studies show that Earth system models (ESMs) do not adequately represent surface energy fluxes over the historical era. We investigated global and regional aerosol effects over the time period 1961-2014 by looking at surface downwelling shortwave radiation (SDSR).
We used observations from ground stations as well as multiple experiments from five ESMs participating in the Coupled Model Intercomparison Project Version 6 (CMIP6). Our results show that this subset of models reproduces the observed transient SDSR well in Europe, but poorly in China. 
The models do not reproduce the observed trend reversal in SDSR in China in the late 1980s, which is attributed to a change in the emission of SO₂ in this region. The emissions of SO₂ show no sign of a trend reversal that could explain the observed SDSR evolution over China, and neither do other aerosols relevant to SDSR. The results from various aerosol emission perturbation experiments from DAMIP, RFMIP and AerChemMIP suggest that its likely, that aerosol effects are responsible for the dimming signal, although not its full amplitude. Simulated cloud cover changes in the different models are not correlated with observed changes over China.  Therefore we suggest that the discrepancy between modeled and observed SDSR evolution is partly caused by erroneous aerosol and aerosol precursor emission inventories. This is an important finding as it may help interpreting whether ESMs reproduce the historical climate evolution for the right or wrong reason.

How to cite: Moseid, K. O., Schulz, M., Storelvmo, T., Julsrud, I. R., Olivié, D., Nabat, P., Wild, M., Cole, J. N. S., and Takemura, T.: Bias in CMIP6 models compared to observed regional dimming and brightening trends (1961-2014), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3349, https://doi.org/10.5194/egusphere-egu2020-3349, 2020.

The stable nitrogen isotope ratios (δ¹⁵N) of total nitrogen (TN) were studied for fine aerosol particles (PM₁) collected with a 24-h time resolution every two days at a Central European rural background site from September 27, 2013, to August 9, 2014 (n=146).
We observed a seasonal cycle of enrichment and depletion of ¹⁵N in aerosol particles with lower values in winter and higher values in summer. The majority of the yearly data showed a strong correlation between δ¹⁵N and ambient temperature, supporting an enrichment of ¹⁵N via isotopic equilibrium exchange between the gas and particulate phases. This process seemed to be one of the main mechanisms for ¹⁵N enrichment at the Košetice site, especially during spring. The most ¹⁵N-enriched summer and most ¹⁵N-depleted winter samples were limited by the partitioning of nitrate in aerosols and suppressed equilibrium exchange between gaseous NH₃ and aerosol NH₄⁺. During winter, we observed an event with the lowest δ¹⁵N values which deviate from temperature dependence. The winter event was connected with prevailing southeast winds and the lowest δ¹⁵N values were probably associated with agriculture emissions of NH₃ under low-temperature conditions (<0°C).

Acknowledgement:
This conference contribution was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project No. LM2018122, by the ERDF project "ACTRIS-CZ RI" (No. CZ.02.1.01/0.0/0.0/16_013/0001315) and by the Japan Society for the Promotion of Science (JSPS) through Grant-in-Aid No. 24221001. We appreciate the financial support of JSPS fellowship to P. Vodička (P16760) in Japan.

Reference:
Vodička, P., Kawamura, K., Schwarz, J., Kunwar, B. and Ždímal, V.: Seasonal study of stable carbon and nitrogen isotopic composition in fine aerosols at a Central European rural background station, Atmos. Chem. Phys., 19, 3463–3479, 2019.

How to cite: Vodička, P., Kawamura, K., Schwarz, J., Kunwar, B., and Ždímal, V.: Seasonal changes in stable nitrogen isotopic composition in fine aerosols at a rural background station Košetice (Central Europe)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3469, https://doi.org/10.5194/egusphere-egu2020-3469, 2020.

Molecular markers in ambient organic aerosol (OA) are valuable in providing source information and insights to formation process of OA. Their traditional quantification is based on offline analysis of filter samples, hugely hindering the utility of the tracer data due to the coarse time resolution and labor-intensive nature. In this study, hourly organic molecular markers in fine particulate matter were measured using a recently commercialized Thermal desorption Aerosol Gas chromatography-mass spectrometry (TAG) at an urban location in Shanghai, China during a three-week campaign from 9 November-3 December 2018. Anhydro sugars, fatty acids, aromatic acids, and polycyclic aromatic hydrocarbons (PAHs) were examined in detail. Their diurnal variations showed characteristic features representing the corresponding emission source activities. For example, stearic acid showed a clear peak around 7 pm, in accordance with the enhanced cooking activities during mealtime. Diagnostic ratios of related maker species of different reactivity provided unique information in uncovering the source information and tracking evolution of OA in the atmosphere. For example, Levo/Manno and Levo/K⁺ ratio analysis identified crop residue burning as the major form of biomass burning. Ratios of unsaturated and saturated fatty acids gave unambiguous indication of atmospheric degradation of unsaturated fatty acids after emissions. Furthermore, oleic acid to stearic acid ratio was highly correlated with O/C ratios, suggesting the possible utility of oleic acid as a model compound to examine the heterogeneous reaction of cooking-related OA. PAH ratio-ratio plots helped tag varying influences of major combustion sources associated with air masses of different origins, with coal combustion and biomass burning dominant under the influence of long range transport air mass and vehicle emissions dominant under local/median range air mass influence. This study demonstrated the utility of the hourly organic markers in capturing the dynamic change of the source emissions and atmospheric ageing, providing observational evidence to support their use in rapid source apportionment.

How to cite: Wang, Q., He, X., Zhou, M., Huang, D., Qiao, L., Zhu, S., Ma, Y., Wang, H., Li, L., Huang, C., Xu, W., Worsnop, D., Goldstein, A. H., Guo, H., and Yu, J. Z.: Primary Organic Aerosol Source Identification and Aging Observed by Hourly Measurements of Organic Molecular Markers in Urban Shanghai, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3431, https://doi.org/10.5194/egusphere-egu2020-3431, 2020.

Laboratory measurement of the particle size distribution and cloud condensation nucleation activation ratio are conducted using two types of synthetic ice nuclei (IN). New Engineered Organic Nuclei (NEON) are fabricated by fermentation and so-called E-lysis of Gram-negative bacteria, which are havested via centrifugation and resuspended in a NaHCO₃ buffer (pH of ~7.8) for final inactivation of lysis escape muntants. NEON is inactivated using 1.25 % (final concentration) glutaraldehyde (GA) and stored in a deep freezer. The NEON with GA solution is atomized using a Sparging Liquid Aerosol Generator (SLAG), which does not sheer or impact the aerosols. The measured size distribution is compared to aerosols produced by the TSI Atmomizer (Model 3076), which impacts generated droplets. The size distribution is measured using a TSI Scanning Mobility Particle Sizer Spectrometer (SMPS) and a TSI Aerodynamic Particle Sizer. A DMT Cloud Condensation Nuclei Counter (CCNC) operated at 0.6 % supersaturation and a TSI Condensation Particle Counter (CPC) is used to measure the activation ratio, which is important to determine effectiveness of the NEON as an immersion ice nuclei. The NEON results are compared to IN produced by burning silver iodine cloud seeding flares.

How to cite: Delene, D., Peske, E., Rauscher, M., and Lubitz, W.: Laboratory Measurements of the Size Distribution and Activation Ratio of Synthetic Ice Nuclei, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3722, https://doi.org/10.5194/egusphere-egu2020-3722, 2020.

Benefited from the tightening emissions of air pollutants, a large annual decrease in mixing ratio of SO₂ and a moderate decrease in PM_2.5 can be identified in northern China since 2014. However, a few extreme PM_2.5 pollution events still occur for sometimes during heating seasons, e.g., the 99th percentile value of PM_2.5 concentrations during the heating season in 2018 had exceeded 200 µg m^-3 therein. One unit of percentile value corresponds to approximately 30 hours. To reveal real causes of these extreme PM_2.5 pollution events, we define two technical terms in this study, i.e., 1) secondary particulate species formed in ambient air (conventionally-defined FSPM); 2) formation of secondary particulate matter in the fresh plumes during the initial several minutes (plume-processed FSPM). We also introduce a metric, i.e., PM_2.5/CO in unit of µg m^-3 / ppm. With these technical terms in mind, we then struggle to dissect real mechanisms causing the severe PM_2.5 pollution event in 11-14 January 2019 across norther China. A staircase function of ratios of PM_2.5/CO against PM_2.5 rather than a linear increase or decrease with PM_2.5 generally occurred through the event. However, in general, larger ratios of PM_2.5/CO were indeed observed with larger concentration of PM_2.5. Regarding frequently observed invariant ratios accompanying with large variations in PM_2.5, larger ratios are, however, probably not caused by conventionally-defined FSPM in PM_2.5. Alternatively, our further multiple-technical analysis results confirm plume-processed FSPM, followed by accumulation under poor meteorological conditions, dominatingly resulting in the severe event. 

How to cite: Yao, X., Zhu, Y., and Meng, H.: Small contribution of conventionally-defined formation of secondary particulate matter to severe PM2.5 pollution in today’s northern China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4556, https://doi.org/10.5194/egusphere-egu2020-4556, 2020.

Amines reportedly overwhelm ammonia in generating new particles through neutralizing sulfuric acid vapor even with several orders smaller concentrations of amines against ammonia in ambient air, demonstrating an attractive prospect in adjusting concentrations of amines to adjust aerosol number loadings, alleviate air pollution and manipulate aerosol cooling effects. Due to lack of in-situ observations, real competition of amines against ammonia in ambient air to be neutralized by acids remains poorly understood. Here, successful semi-continuous measurements of gaseous amines and ammonia and their particulate partners in marine atmospheres reveal that atmospheric trimethylamine (TMA_gas) unable to compete with NH_3gas and to form particulate trimethylaminium (TMAH⁺), but the particulate TMA (TMA_particulate) is detectable and comparable to TMA_gas under NH_3gas <1.0 µg m^-3. Contradictory to the common knowledge, the preexisting TMA_particulate is largely depleted in strong SO₂ plumes with abundant acids and even depleted NH_3gas. A two-aerosol-phase transfer concept model is proposed to interpret the new findings, but no single-phase acid-base neutralization reactions can. In contrast, observational evidences confirm that gaseous dimethylamine (DMA_gas) plus particulate dimethylaminium (DMAH⁺) overwhelmingly exist as DMAH⁺ under atmospheric NH₃ (NH_3gas) <0.3 µg m^-3 versus DMA_gas under NH_3gas >1.8 µg m^-3, respectively. The neutralization of DMA_gas to form DMAH⁺ is always enhanced in strong SO₂ plumes, almost independent on NH_3gas. Thermodynamically, DMA_gas may act as a competitor in generating secondary particles only under low NH_3gas or in SO₂ plumes.

How to cite: Chen, D., Zhu, Y., Shen, Y., and Yao, X.: Real neutralization reactions of amines against ammonia by acids in ambient air, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5064, https://doi.org/10.5194/egusphere-egu2020-5064, 2020.

How to cite: Besel, V., Kubečka, J., Kurtén, T., and Vehkamäki, H.: New Particle Formation Involving Charged Sulfuric Acid – Ammonia Clusters , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5152, https://doi.org/10.5194/egusphere-egu2020-5152, 2020.

The ability of particulate matter (PM) to generate reactive oxygen species and induce oxidative stress in human body is known as oxidative potential (OP). OP is considered an important indicator of the toxicity of PM, which is associated with adverse health impacts. Linking the predicted health impacts of aerosols to OP may be more relevant than considering PM mass only. In this study, we determined the OP of PM_2.5 (PM with aerodynamic diameter less than 2.5 µm) in Dammam, Saudi Arabia, in order to understand the relationship of OP to PM mass and composition in the present and absent of dust storm.
PM_2.5 was collected from two locations in Dammam city in the winter and summer of 2018. The first location was the city centre as an urban area while the second one was in the campus of Imam Abdulrahman Bin Faisal University as an urban background area. OP was quantified using dithiothreitol (DTT) assay. The mean PM_2.5 mass in the summer (120.5 µg/m³) was nearly  twice that in the winter (62.6 µg/m³). The average OP activity per air volume (DDTv) in the winter was 1.14 nmol min^-1 m^-3 while in the summer it was 1.77 nmol min^-1 m^-3. Conversely, the mean OP activity per PM mass (DDTm) in the winter was 24.56 pmol min^-1 µg^-3 while it was lower in the summer at 17.3 pmol min^-1 µg^-3. Results showed an inverse correlation between PM mass and DDTm, while there was a positive correlation between PM mass and DDTv. Even though the average mass of PM_2.5 in the summer was almost twice that in the winter, the average DDTm was lower in the summer compared to winter. This is due to the much lower oxidative potential in dust storm particles, which contribute significantly to the summertime PM_2.5. Our results suggest that OP is driven by PM composition rather than mass. 

How to cite: Alwadei, M., Thomson, S., Kramer, L., Shi, Z., and Bloss, W.: Oxidative Potential of PM2.5 in Dammam, Saudi Arabia, and the effect of dust storms., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5727, https://doi.org/10.5194/egusphere-egu2020-5727, 2020.

Brown carbon (BrC) is a type of light-absorbing organic compounds with a high capacity to absorb light in the low-wavelength visible and near-ultraviolet regions, which is ubiquitous in atmospheric aerosols, rainwater, and cloudwater samples. BrC can not only alter the light absorption and radiative forcing of aerosols but can also influence the formation of cloud condensation nuclei; therefore, it has a potential impact on atmospheric chemistry and climate change. Numerous studies have demonstrated that combustion processes are significant sources of atmospheric BrC, however most of these studies were focused on the emissions of biomass burning. Knowledge of primary BrC from coal combustion is still limited. In the study, smoke particles emitted from the combustion of residential coals with different geological maturity were collected in a combustion system. Then BrC fractions, including water soluble organic carbon (WSOC), water soluble humic-like substances (HULIS_w), alkaline soluble organic carbon (ASOC) and methanol soluble organic carbon (MSOC) were extracted and characterized for their abundances, chemical, and light absorption properties.

Our results showed that the abundance and light absorption of the coal combustion-derived BrC fractions were strongly dependent on the extraction methods used and the coal maturity. The abundances of MSOC fraction was significantly higher than WSOC and ASOC fractions and even higher than the sum of WSOC and ASOC, indicating that most organic compounds in smoke particles were soluble in pure methanol. The WSOC and MSOC fractions from the combustion of low maturity coal had relatively low SUVA₂₅₄ and MAE₃₆₅ values, indicated that they had relatively low levels of aromatic structures and light absorption.

The WSOC and MSOC fractions were characterized by ultrahigh-resolution mass spectrometry. The results showed that S-containing compounds (CHOS and CHONS) are found to be the dominant components of the WSOC, whereas CHO and CHON compounds make a great contribution to the MSOC samples. Noted that a greater abundance of S-containing compounds was found in the smoke produced from coal combustion compared to biomass burning and atmospheric samples, indicated that coal combustion could be an important source of atmospheric S-containing compounds in certain areas. The findings also suggest that organic molecules with a high aromaticity index and low polarity showed stronger light absorption. In summary, our study indicated that coal combustion is a potential source of atmospheric BrC and their abundance, chemical, and light absorption were strongly dependent on the extraction methods used and the coal maturity.

How to cite: Song, J., Li, M., Fan, X., and Peng, P.: Chemical composition and light absorption of brown carbon emitted from residential coal combustion in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6259, https://doi.org/10.5194/egusphere-egu2020-6259, 2020.

How to cite: Lee, H., Lee, K., Krejci, R., Aas, W., Park, J., Park, K., Lee, B. Y., Yoon, Y.-J., and Park, K.: New particle formation characteristics in the Arctic (Zeppelin, Svalbard) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6530, https://doi.org/10.5194/egusphere-egu2020-6530, 2020.

The impact of brown carbon aerosol (BrC) on the Earth’s radiative forcing balance has been widely recognized but remains uncertain, mainly because the relationships among BrC sources, chromophores, and optical properties of aerosol are poorly understood (Feng et al., 2013; Laskin et al., 2015). In this work, the light absorption properties and chromophore composition of BrC were investigated for samples collected in Xi’an, Northwest China from 2015 to 2016. Both absorption Ångström exponent and mass absorption efficiency show distinct seasonal differences, which could be attributed to the differences in sources and chromophore composition of BrC. Three groups of light-absorbing organics were found to be important BrC chromophores, including those show multiple absorption peaks at wavelength > 350 nm (12 polycyclic aromatic hydrocarbons and their derivatives) and those show single absorption peak at wavelength < 350 nm (10 nitrophenols and nitrosalicylic acids and 3 methoxyphenols). These measured BrC chromophores show distinct seasonal differences and contribute on average about 1.1% and 3.3% of light absorption of methanol-soluble BrC at 365 nm in summer and winter, respectively, about 7 and 5 times higher than the corresponding mass fractions in total organic carbon. The sources of BrC were resolved by positive matrix factorization (PMF) using these chromophores instead of commonly used non-light absorbing organic markers as model inputs. Our results show that in spring vehicular emissions and secondary formation are major sources of BrC (~70%), in fall coal combustion and vehicular emissions are major sources (~70%), in winter biomass burning and coal combustion become major sources (~80%), while in summer secondary BrC dominates (~60%).

References:

Feng, Y., V. Ramanathan, and V. R. Kotamarthi: Brown carbon: A significant atmospheric absorber of solar radiation?, Atmos. Chem. Phys., 13, 8607-8621, doi:10.5194/acp-13-8607-2013, 2013.

Laskin, A., J. Laskin, and S. A. Nizkorodov: Chemistry of atmospheric brown carbon, Chem. Rev., 115, 4335-4382, doi:10.1021/cr5006167, 2015.

How to cite: Huang, R.-J., Yuan, W., Yang, L., Guo, J., Duan, J., and Ni, H.: Light absorption properties, chromophore composition and sources of brown carbon aerosol in Xi’an, Northwest China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6702, https://doi.org/10.5194/egusphere-egu2020-6702, 2020.

 In Seoul, PM_2.5 concentrations were frequently elevated with O₃ in May 2019. The most abundant constituent of PM_2.5 was nitrate, which was the best correlated with OC (organic carbon) as well as NH₄⁺. An intensive experiment was conducted in the eastern part of Seoul from March 29 to June 19, 2019. Measurement was made for PM_2.5 and its chemical composition including NO₃^-, SO₄^2-, NH₄⁺ , OC, EC (elemental carbon), and reactive gases including O₃, NO, NO₂, CO, HONO, HNO₃, NH₃, and SO₂, and meteorological variables including vertical winds and mixed layer height (MLH). The particle number concentration was measured using SMPS (Scanning Mobility Particle Sizer). All measurements were averaged for 1 hour according to the resolution of PM_2.5 chemical composition. For the entire experiment, the mean mass concentrations of PM_2.5, NO₃^-, SO₄^2-, NH₄⁺, OC, and EC were 20.40 μg/m³, 4.07 μg/m³, 2.62 μg/m³, 2.01 μg/m³, 4.01 μg/m³, and 1.04 μg/m³, respectively. For reactive gases, the mean concentration was 1.03 ppbv for HONO, 0.70 ppbv for HNO₃, 14.87 ppbv for NH₃, 2.77 ppbv for SO₂, and 48.79 ppbv for O₃. 

 The maximum PM_2.5 concentration of 72.81 μg/m³ was observed under the influence of weak Asian dust event in the end of April. In May, there were three distinct episodes with highly enhanced PM_2.5. In the early May, the maximum nitrate concentration (36.11 μg/m³) was observed with high HONO (2.41 ppbv) on 4 May. In the middle of May, PM_2.5 was raised with SO₄^2- under stagnant condition. On 25 May, PM_2.5 was raised up to 92 μg/m³ with high nitrate concentration (18.56 μg/m³) , when O₃ reached 205 ppbv. In this episode, O₃ concentration remained around 90 ppbv at night and OC and EC were well correlated with highly enhanced K⁺. Thus, the concurrent enhancement of PM_2.5 and O₃ was likely due to the influence of aged biomass combustion plume laden air transported from southeast China. At the same time, HNO₃ and HONO concentration was highly elevated, indicating that heterogeneous reactions played a role.

How to cite: Son, J., Kang, S., Kim, J., Gil, J., Lee, M., Lee, T., Park, M., and Heo, G.: Concurrent increases of PM2.5 and Ozone observed in Seoul, May 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7020, https://doi.org/10.5194/egusphere-egu2020-7020, 2020.

Ammonium nitrate (NH₄NO₃) is the main driver of high PM_2.5 episodes in Seoul, but its formation processes are not fully understood yet. Intensive experiments were conducted at the Korea University campus in Seoul during June ~ August 2018 and April ~ June 2019, when the chemical composition of PM_2.5 including Na⁺, SO₄^2-, NH₃, NO₃^-, Cl^-, Ca²⁺, K⁺, Mg²⁺, OC and EC, and its gaseous precursors including NO_X, HNO₃ and SO₂ were continuously measured. The concentrations of PM_2.5 and its major constituents were noticeably higher in pre-monsoon (June) than summer monsoon (July~August) period. In particular, nitrate concentration was much higher (6.9 μg/m³) during the high PM_2.5 episode (24-hr average PM_2.5 > 35 μg/m³) in June compared to those of non-episode (3.1 μg/m³) and the other two months (0.74 μg/m³). Aerosol liquid water content (ALWC) was calculated using ISORROPIA II model, ALWC was higher during the episode than non-episode and the highest ALWC was found concurrently with the highest NO₃^- concentration (18.2 μg/m³) at night. Concurrent increases of nitrate and ALWC cause aqueous-phase formation and hygroscopic growth of aerosol, which lead to high PM_2.5 concentration. In addition, ALWC was more rapidly increased with the number of accumulation mode particles larger than 100 nm in diameter at higher RH and nitrate concentration. In this study, PM_2.5 mass and nitrate were elevated after the NO_X peak in the morning as well as at dawn. The surface of pre-existing particles was found to be prerequisite for nitrate driven PM_2.5 episode.

How to cite: Park, J., Lim, S., Lee, M., Lee, T., Park, M., Heo, G., and Kim, C.: Nitrate-driven high PM2.5 episodes in Seoul during pre-monsoon season, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7050, https://doi.org/10.5194/egusphere-egu2020-7050, 2020.

Volatile organic compounds (VOCs) are the key precursors of O­₃ and secondary organic aerosols in urban atmosphere. This study investigates the variations and emission sources of 55 VOCs observed in central Seoul between 2013 and 2019. VOCs were continuously measured every hour using an online gas chromatography system by the Seoul Metropolitan Government Research Institute of Public Health and Environment (SIHE). The lower limit of detection was 0.1 ppbC and outliers were removed by applying Chauvenet’s criterion.

Of the 55 VOCs, the most abundant species was ethane, followed by propane and toluene and their average concentrations were 6.6 ppbv, 5.9 ppbv and 4.6 ppbv, respectively. In terms of TVOCs, toluene was the most abundant with the average concentration of 32.1 ppbC and comprises about the half of the aromatic VOCs. Alkane and aromatics showed different seasonal, diurnal and weekly variations, and dependence on meteorological variables. In addition, the toluene to benzene ratio was greater in summer than in winter with the average of 11.0. These results indicate the additional sources for VOCs to traffic related emissions in megacity Seoul. The PSCF (Potential Source Contribution Function) and cluster analysis of backward trajectories of air masses indicate that while alkanes are chiefly emitted from vehicles, aromatic concentrations are greatly influenced by fugitive emission from neighboring cities of Seoul. There is also chance for some VOCs with relatively long lifetime to be transported from nearby countries.

How to cite: Kang, S., Son, J., Kim, J., Lee, M., and Lee, J.: Characterization of volatile organic compounds (VOCs) in megacity Seoul from multiyear observation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7071, https://doi.org/10.5194/egusphere-egu2020-7071, 2020.

Aerosol from open biomass burning (BB) is known to strongly impact the Earth radiation budget. Therefore, a good knowledge of its optical properties and their evolution is an important prerequisite for accurate assessments of contributions of various factors to climate change by means of chemistry-transport and climate models. As a major component of typical BB aerosol is organic matter, the atmospheric evolution of BB aerosol can be strongly affected by the physical and chemical processes governing the gas-particle partitioning of organic compounds. Recently, it has been shown [1] that these processes can give rise to strongly nonlinear behavior of mass concentration of organic fraction of BB aerosol during its atmospheric lifetime. It has been also argued that chemical and physical nonlinearities can explain part of the observed diversity of the effects of BB aerosol atmospheric aging. The present study has extended the previous analysis of the nonlinear behavior of BB aerosol, focusing on the evolution of BB aerosol optical properties, such as, specifically, mass absorption and scattering efficiencies (MAE and MSE) in the near-UV and optical wavelength ranges. The evolution of aerosol in BB plumes was simulated with the MDMOA [1] microphysical box model that involves a schematic parameterization of the dilution process and represents the oxidation and gas-particle partitioning processes within the volatility basis set (VBS) framework. The Mie-theory-based simulations of the optical properties of aging BB aerosol were performed with the OPTSIM module [2] coupled with MDMOA. The simulations show that both MAE and MSE can exhibit strong and diverse changes during BB aerosol evolution mostly due to significant changes in the aerosol particle size distribution. Furthermore, similar to the mass concentration, both MAE and MSC of the aged BB aerosol depend in a nonlinear manner on the initial BB aerosol concentration and the initial size of a smoke plume and are sensitive to the choice of a concrete VBS scheme. The results of this study may have important implications for modeling of radiative effects of BB aerosol with chemistry-transport and climate models and for interpretation of remote observations of BB aerosol.

The study was supported by the Russian Foundation for Basic Research (grant No. 18-05-00911).

References

1. Konovalov, I. B., Beekmann, M., Golovushkin, N. A., and Andreae, M. O.: Nonlinear behavior of organic aerosol in biomass burning plumes: a microphysical model analysis, Atmos. Chem. Phys., 19, 12091–12119, https://doi.org/10.5194/acp-19-12091-2019, 2019.
2. Stromatas, S., Turquety, S., Menut, L., Chepfer, H., Péré, J. C., Cesana, G., and Bessagnet, B.: Lidar signal simulation for the evaluation of aerosols in chemistry transport models, Geosci. Model Dev., 5, 1543–1564, https://doi.org/10.5194/gmd-5-1543-2012, 2012.

How to cite: Golovushkin, N., Konovalov, I., and Beekmann, M.: Effects of physical and chemical nonlinearities on evolution of optical properties of biomass burning aerosol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7118, https://doi.org/10.5194/egusphere-egu2020-7118, 2020.

Secondary organic aerosols (SOA) are a large fraction of PM_2.5 mass and contribute to extreme haze events, reducing visibility and impairing human health, especially in the Northern China Plain. It has been observed that laboratory generated and field collected SOA material can undergo liquid-liquid phase separation (LLPS), however this has never been directly observed in single ambient aerosol particles. Oligomers are a significant component of atmospheric SOA typically having a molecular mass of >200 g mol^-1. These large molecules can be produced via multiphase chemical processes and, when soluble in the aerosol phase, may lead to interesting phase separation behavior.

We conducted a campaign in Beijing during which PM_2.5 was analyzed using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) to observe oligomers at significant quantities. Aerosol particle samples collected before, during and at the peak of a pollution event were targeted. We have evidence that oligomers were the result of multiphase chemistry at high relative humidity. Single particles were probed for chemical morphology and mixing states using X-ray spectro-microscopy to characterize the numbers of particles mixed with inorganic matter, organic matter or soot. Using an environmental microchamber, we subjected single ambient particles to humidity cycles and observed any LLPS to occur. We also quantify the humidity required for LLPS to occur. Our data links oligomeric material having different solubility than e.g. inorganic hygroscopic components with LLPS, giving rise to a clear constraint for urban haze. The results will give statistically significant information about particle mixing state for aerosol population having different oligomer content, humidity history, LLPS behavior and pollution levels.

How to cite: Yang, S., Alpert, P., Xu, Y., Duan, F., He, K., and Ammann, M.: Mixing States of Aerosol Particles in Urban Haze, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7202, https://doi.org/10.5194/egusphere-egu2020-7202, 2020.

In this study, simplified analytic type of expression for size dependent MEs (Mass efficiencies) are developed. The entire size was considered assuming lognormal size distribution for sulfate, nitrate and NaCl aerosol species and the MEE of each aerosol chemical composition was estimated by fitting Mie’s calculation. The obtained results are compared with the results from the Mie-theory-based calculations and showed comparable results.

The mass efficiencies of all aerosol components for each size range are compared with Mie’s results and approximated as a function of geometric mean diameter in the form of a power law formula. Finally, harmonic mean type approximation was used to cover entire particle size range.

Also, analytic expression of approximated scattering enhancement factor which stands for the effect of hygroscopic growth factor for polydispersed aerosol on aerosol optical properties are obtained.

Based on aerosol thermodynamic models, mass growth factor can be obtained and their optical properties can be obtained by using Mie theory with different aerosol properties and size distribution. Finally, scattering enhancement factor was approximated fRH for polydispersed aerosol as a function of RH.

Finally, we also compared the simple forcing efficiency (SFE, W/g) of polydisperse aerosols between the developed simple approach and by the method using the Mie theory. The results show that current obtained approximated methods are comparable with existing numercal calculation based results for polydipersed particle size.

How to cite: Jung, C. H., Lee, J., Um, J., and Kim, Y. P.: Reconstructed expression for aerosol extinction coefficient by considering mass extinction efficiency and hygroscopic growth for polydipersed aerosol, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7475, https://doi.org/10.5194/egusphere-egu2020-7475, 2020.

The biomass burning over West Africa during the dry season (December – February) is a globally significant source of trace gases and carbonaceous aerosol particles in the atmosphere. The MOYA-2017 (Methane Observations Yearly Assessments 2017) campaign were conducted using the UK FAAM Bae-146 airborne research aircraft, to investigate biomass burning emissions in this region. Research sorties were flown out of Senegal, with some flights directly over terrestrial fires and others sampling transported smokes over the Atlantic ocean.

The aircraft was equipped with a variety of aerosol-related instruments to measure submicron aerosol chemical properties (aerosol mass spectrometer, AMS and single-particle soot photometer, SP2) and absorption at different wavelengths (Photoacoustic spectrometer, PAS, measure at 405, 514 and 658 nm). In this study, we focus on the aging process of ambient black carbon (BC) and brown carbon (BrC) from biomass burning, in time scale from (<0.5) h to (9 – 15) h. The transport age of smokes was estimated using Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME).

The sampled smokes during MOYA-2017 were controlled by flaming-phase combustion. The enhancement ratios of BC with respect to CO ranged from 14 to 26 (ng m^–3 / ppbv) at sources. Our measurements show that count and mass median diameters of BC core size were relatively stable, which were around 106 and 190 nm respectively. Average BC coating thickness increased from (1.16 ± 0.03) to (1.71 ± 0.06) after approximately half-day transport. Average absorption angstrom exponents (AAE_405-658) increased from (1.1 ± 0.1) to (1.8 ± 0.3), suggesting that BrC contributed little in the very freshly emitted aerosols (<0.5 h) and were formed during aging process. In order to investigate the importance of BrC in this area, we also attributed the measured aerosol absorption into BC and BrC separately. By linking AAE_405-658 with organic (OA) composition measured by the AMS, we found that the increasing AAE_405-658 is positively correlated with O/C ratio (oxygenation) of the OA. These data indicate that BrC in smokes controlled by flaming combustion is likely to be from the condensation of semi-volatile OA during cooling stage of smokes, and from the aged primary OA or secondary OA formation.

How to cite: Wu, H., Taylor, J., Langridge, J., Yu, C., Williams, P., Flynn, M., and Coe, H.: The aging process of ambient black carbon and brown carbon from biomass burning emission during MOYA-2017 aircraft campaign, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8743, https://doi.org/10.5194/egusphere-egu2020-8743, 2020.

The Particle Size Magnifier (PSM, Airmodus) [1] is able to size sub 3 nm particles in mobility diameter. A PSM‘s sensitivity and cutoff size (50% detection efficiency) is usually calibrated only with particles out of metal oxides, e.g. tungsten oxide [2], or with different salt particles [1]. The PSM used in this experiment has a cutoff size for ammonium sulfate particles of 1.3 nm in mobility diameter. Ternary nucleation in the atmospheric boundary layer, however, involves organic molecules. It is therefore questionable, if the inorganic calibration curves of the PSM can be applied to these particles.

In this study we aim to understand the PSM‘s response to purely biogenic particles as well as to highly oxidized molecules (HOMs) with carbon backbones of different sizes (C₁₀-, C₁₅-, C₂₀- and C₃₀-HOMs). We used a flow reactor with a short reaction time of about 9s that allows for undisturbed radical – radical reactions due to negligible wall contacts to quantitatively generate HOMs by ozonolysis of different precursors. Reactants were ozone and either alpha-Pinene (C₁₀H₁₆) or beta-Caryophyllene (C₁₅H₂₄) with and without an OH-scavenger.

A recent study [3] demonstrated, that the ozonolysis of alpha-Pinene produces covalently bound C₂₀-HOMs from self- and cross-reactions of two C₁₀-peroxy radicals. The C₃₀-HOMs are formed equivalently from C₁₅-radicals of beta-Caryophyllene oxidation. This mechanism shows, why the C₂₀- and C₃₀-HOMs increase quadratically, in contrast to the C₁₀- and C₁₅-HOMs, that increase linearly with respective reacted precursor concentrations. Making use of this principle, we are able to show, that already C₂₀-HOMs are detected by the PSM, but with a much smaller detection efficiency than the C₃₀-HOMs, that have an ion mobility diameter of approximately 1.6 nm. Our size-dependent calibration gave a steep sensitivity increase around the particle size of about 1.8 nm mobility diameter for organic particles, showing, that organics are far more difficult to detect than ammonium sulfate particles.

[1] J. Vanhanen, J. Mikkilä, K. Lehtipalo, M. Sipilä, H. E. Manninen, E. Siivola, T. Petäjä & M. Kulmala (2011) Particle Size Magnifier for Nano-CN Detection, Aerosol Science and Technology, 45:4, 533-542, DOI: 10.1080702786826.2010.547889

[2] J. Kangasluoma, M. Attoui, H. Junninen, K. Lehtipalo, A. Samodurov, F. Korhonen, N. Sarnela, A. Schmidt-Ott, D. Worsnop, M. Kulmala, T. Petäjä (2015) Sizing of neutral sub 3nm tungsten oxide clusters using Airmodus Particle Size Magnifier, Journal of Aerosol Science, 87, 53-62, DOI: https://doi.org/10.1016/j.jaerosci.2015.05.007

[3] T. Berndt, B. Mentler, W. Scholz, L. Fischer, H. Herrmann, M. Kulmala, A. Hansel (2018) Accretion Product Formation from Ozonolysis and OH Radical Reaction of α-Pinene: Mechanistic Insight and the Influence of Isoprene and Ethylene, Environ. Sci. Technol. 2018, 52, 19, 11069-11077, DOI: https://doi.org/10.1021/acs.est.8b02210

How to cite: Scholz, W., Rörup, B., Leiminger, M., Steiner, G., Lehtipalo, K., Kangasluoma, J., and Hansel, A.: Can Particle Size Magnifiers detect HOMs with carbon numbers between C10 and C30?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9468, https://doi.org/10.5194/egusphere-egu2020-9468, 2020.

Cloud-aerosol interactions give rise to much of the uncertainty in estimates of climate forcing, climate sensitivity and thus also future climate predictions. Furthermore, the modelled concentration of cloud condensation nuclei (CCN) in the past, present and future are highly dependent on the how the models represent new particle formation (NPF) – a process which is both poorly understood theoretically and difficult to model due to its complex nature. Global modellers in particular have to prioritize between theoretical accuracy and keeping computational costs low. A common approach in these models is to use a modal scheme to parameterize the sizedistribution of the aerosols, while sectional schemes are in general considered closer to first principals.

To better capture the dynamics of early growth in the Norwegian Earth System Model (NorESM), we have implemented a sectional scheme for the smallest particles (currently 5 - 39 nm), which proceeds to feed particles into the original modal scheme (Kirkevåg et al, 2018) after growth. The sectional scheme includes two species, H₂SO₄ and low volatile organics and has 5 bins. The motivation is: (1) In the original scheme in NorESM, newly formed particles are added to the smallest mode which has a number median diameter of 23.6 nm. The survival of particles from NPF (formed at ~4 nm diameter) to this mode is calculated based on Lehtinen et al (2007). Thus it does not take into account dynamics within this size range, i.e. competition for condensing vapours and growth of particles over more than one time step. (2) Including a sectional scheme in this range adds precision for this crucial stage of growth while keeping the computational cost low due to the limited number of species involved (currently 2 in the model). (3) A sectional scheme within this size range is an interesting alternative to a nucleation mode, which is known to have problems with moving particles to larger sizes at the same time as adding newly formed particles.

We present several sensitivity tests which investigate the response of the model to changes in emissions of SO₂ and biogenic volatile organic compounds and nucleation parameterizations, with and without the sectional scheme. Our results in particular show that in the globally averaged boundary layer, the sectional scheme drastically reduces the number of particles that survive to the modal scheme compared the original model, while more particles survive in remote regions. On the other hand, the sectional scheme is less sensitive to the choice in NPF/nucleation parameterization. 

References: 

Lehtinen, Kari E. J., Miikka Dal Maso, Markku Kulmala, and Veli-Matti Kerminen. "Estimating Nucleation Rates from Apparent Particle Formation Rates and Vice Versa: Revised Formulation of the Kerminen–Kulmala Equation." Journal of Aerosol Science 38, no. 9 (September 1, 2007): 988–94. https://doi.org/10.1016/j.jaerosci.2007.06.009.

Kirkevåg, A., A. Grini, D. Olivié, Ø. Seland, K. Alterskjær, M. Hummel, I.H.H Karset, A. Lewinschal, X. Liu, R. Makkonen, I. Bethke, J. Griesfeller, M. Schulz and T. Iversen. "A production-tagged aerosol module for Earth system models, OsloAero5.3 – extensions and updates for CAM5.3-Oslo." Geoscientific Model Development 11. no. 10 (October, 2018): 3945--3982. https://doi.org/10.5194/gmd-11-3945-2018

How to cite: Blichner, S. M., Sporre, M. K., Makkonen, R., and Berntsen, T. K.: Combination of aerosol sectional scheme and modal scheme in NorESM: Sensitivities to emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9740, https://doi.org/10.5194/egusphere-egu2020-9740, 2020.

The radiative transfer module of an on-line chemical transport models requires input data from aerosol extinction efficiency, single scatter albedo and asymmetry factor, in order to predict the radiative state of the atmosphere. These aerosol optical properties (aerosol optical depth, AOD), may be integrated vertically for comparison to satellite observations. These optical effects may also influence the shorter wavelengths associated with atmospheric gas photolysis, influencing atmospheric reactivity. These processes may be harmonized in an on-line reaction transport model, such as Environment and Climate Change Canada’s GEM-MACH (GEM: Global Environmental Multi-scale – MACH: Modelling Air quality and Chemistry). Previous photolysis routine in the radiative transfer module, MESSY-JVAL (Modular Earth Sub-Model System), in GEM-MACH, made use of a climatology of aerosol optical properties, and the previous on-line version made use of a homogeneous mixture Mie code for meteorological radiative transfer calculations.

We calculated a new lookup table for the extinction efficiency, absorption and scattering cross sections of each aerosol type. The new version of MESSY-JVAL uses GEM-MACH predicted aerosol size distributions, chemical composition and relative humidity in each vertical column at each time step as input, reads aerosol absorption and scattering cross section data from the new lookup table and calculates aerosol optical properties, that are then used to modify both photolysis and meteorological radiative transfer calculations.

In order to evaluate these modifications to the model, we performed a series of simulations with GEM-MACH with wildfire emissions inputs from the Canadian Forest Fire Emissions Prediction System (CFFEPS) and compared the model AOD output with satellite and AERONET (Aerosol Robotic Network) measurement data. Comparison of the hourly AERONET and monthly-averaged satellite AOD demonstrates major improvements in the revised model AOD predictions. The impact of the updated photolysis rates and meteorological radiative transfer calculations on predictions of oxidant mixing ratios and rates of pollutant oxidation (nitrogen dioxide conversion to nitric acid) will be assessed both within and below the forest fire plume.

How to cite: Majdzadeh, M., Stroud, C., Akingunola, A., Makar, P., Sioris, C., McLinden, C., Zhao, X., Moran, M., and Abboud, I.: Interactive Aerosol Feedbacks on Photolysis Rates in the GEM-MACH Air Quality Model for an Athabasca Oil-Sands Modelling Study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10470, https://doi.org/10.5194/egusphere-egu2020-10470, 2020.

The aircraft measurement for air quality is able to fly in three dimensions within the planetary boundary layer of inland and sea. In this study, the Beechcraft B1900D was modified to build a unique aircraft measurement platform for the measurement of particulate matter and gas. This aircraft has a maximum takeoff weight of 7,765kg and this aircraft is loaded with various air quality measurement equipment. The contents of aircraft modification are as follows. The installed contents for air quality measurement are aircraft aerosol inlets, trace gas inlets, discharge tubes, AIMMS-30, and pylon adapter. The power supply of the measurement equipment replaced the generating capacity of starter generators from 300A to 400A (at DC 28V). In addition, this aircraft was installed on the time synchronization and network system of measurement equipment (HR-ToF-AMS, PTR-ToF-MS, CIMS, etc). Currently, the air quality scientists in Korea have been investigating on long-range transport or local large point sources.

How to cite: Seo, B.-K., Kim, J., Park, S. B., Yu, J., and Lee, M.: A Study on modification of Aircraft Platform for Air Quality Measurement in Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10700, https://doi.org/10.5194/egusphere-egu2020-10700, 2020.

Significant uncertainties are still associated to chemical reaction mechanisms used in atmospheric models, in particular for RO_x radicals (OH, HO₂, RO₂). Recent measurements of radicals in forested areas characterized by low NO_x (NO₂, NO) concentrations indicate that models can significantly overestimate peroxy radical concentrations.^1,2 These results question the ability of models to correctly simulate the oxidative capacity of the troposphere since peroxy radicals are a main source of the hydroxyl radical (OH), one of the most important oxidative species in the atmosphere.³  One possible explanation is the occurrence of heterogeneous processes (uptake of radicals) on the surface of aerosols that are either misrepresented or not included in models. While recent studies have reported uptake coefficients of HO₂ on different types of aerosols, the process is not completely understood yet.

Molecular dynamics combined with ab-initio calculations have been used to study HO₂ reactive uptake on organic aerosols. The sticking process of HO₂ and its reactivity have been modelled on a nanometer size aerosol particle.⁴ Those theoretical calculations provide insight into the uptake process at the molecular scale and are planned to be compared to experimental measurements carried out with an aerosol flow tube.

This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d’investissement d’avenir) and by the regional council “Hauts-de-France”. The authors also thank CPER Climibio and FEDER for their financial support. Calculations were performed using HPC resources from GENCI-TGCC (Grant 2020- A0070801859).

References

• [1] T. Griffith et al., Atmos. Chem. Phys. 13, 5403 (2013)
• [2] Mao et al., Atmos. Chem. Phys. 12, 8009 (2012)
• [3] Stone et al., Chem. Soc. Rev. 41, 6348 (2012)
• [4] Roose et al., ACS Earth Space Chem. 3, 380 (2019)

How to cite: Roose, A., Toubin, C., Dusanter, S., Riffault, V., and Duflot, D.: HO2 reactive uptake on organic aerosols: a molecular level study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11460, https://doi.org/10.5194/egusphere-egu2020-11460, 2020.

This work presents an overview of more than 3-year measurements of ultrafine particle size distributions (PSD, 6-800 nm) at a sub-urban site, the Station for Observing Regional Processes of the Earth System (SORPES) located in Nanjing, Yangtze River Delta of China. For the purpose of understanding the temporal variations as well as the source of ultrafine particles, k-means cluster analysis was applied and seven clusters were finally separated from the PSD data set. PSD spectra, hourly and seasonal frequencies of occurrence, the data of pollutant gases, PM_2.5 and chemical composition, as well as metrological parameters were used to define and interpret each cluster. In general, four clusters (i.e. C1, C2, C3, and C4) were related with new particle formation (NPF) and growth, but they were at different stages or with different intensity, accounting for 20.4% of total PSD data; One (i.e. C5) was attributed to clean regional background, with high level of relative humidity, accounting for 37.9% of total data; Two clusters (i.e. C6 and C7) were polluted clusters, accounting for 41.6% of total data. Two extremely polluted episodes in C6 and C7, respectively, one was caused by fossil fuel combustion and another was caused by biomass burning, were selected as case study. The PSD of two polluted episodes was totally different, even though the mass concentration was similar. The associations between each clusters were analyzed, showing that the contribution of NPF to pollution and the conversion between clean and pollution because of accumulation and wet deposition.

How to cite: Chen, L.: Cluster analysis of ultrafine particle size distribution based on long-term measurement at SORPES in Yangtze River Delta of China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12671, https://doi.org/10.5194/egusphere-egu2020-12671, 2020.

Atmospheric aerosol particles, known for their direct interaction with incoming solar radiations (direct effect) and for perturbation of the cloud properties (indirect effect) by acting as cloud condensation nuclei (CCN), represents largest uncertainty in the current and future understanding of the climate change. In part, this uncertainty is attributed to the lack of accurate measurements of aerosol physical and chemical properties for the improvement of various schemes in prognostic modelling useful for the effective prediction of cloud and precipitation formation. The Indian tropical region, constitutes ~18% of the world’s total population spread heterogeneously over diverse land cover, experiences a distinctive meteorological phenomenon by means of Indian Summer Monsoon (ISM). Thus, the sources, chemical properties and characteristics of aerosols are also expected to have significant variations over the Indian subcontinent depending upon the location and seasons. Online continuous measurements of NR-PM₁ (Non refractory particulate matter ≤1 µm) have been carried out in near real-time using ACSM (Aerosol Chemical Speciation Monitor) at a marine urban location of Chennai, from 4^th January to 2^nd February, 2019, complimented by simultaneous measurements of meteorological parameters. Average NR-PM₁ mass concentration for the duration of the measurements was 30.37±28.31 µg/m³ with organics constituting major fraction of ~47.43% followed by sulphate (~33.34%), ammonium (~11.89%), nitrate (~4.57%) and chloride (~2.74%). Back trajectory analysis using HYSPLIT model enabled the classification of air samples measured in to three periods: “Continental polluted”, “Marine polluted” and “Clean marine”. The polluted periods were distinguished by the potential biomass burning event, which occurs during the regional festival Bhogi, celebrated on 14^th of January in this part of the country. During this period the organics had a peak concentration of 211 µg/m³ followed by chloride ~ 42 µg/m³. During the clean marine period, low mass concentration of PM₁ is attributed to change in meteorological conditions accompanied by airmass originating from the Bay of Bengal. The average mass concentration of NR-PM₁ during this period was observed to be 7.14±2.78 µg/m³, which is ~5 times lesser than the polluted period.

            A comprehensive source apportionment study was carried out using Positive Matrix Factorization (PMF) model implemented through the multilinear engine tool (ME-2) in Source Finder (SoFi) graphical user interface, to understand the contribution of primary and secondary sources to the organic aerosols. Primary anthropogenic emissions contributed on average ~45% (~19% from traffic, ~16.7% from cooking, ~10% from biomass burning) to the total organic mass for entire measurement period, while the major contribution was associated with secondary formation ~55%. On the other hand, for clean marine period, the fractional contribution of secondary formation to PM₁ increased to ~75% to 85%, while that of primary emissions decreased to less than ~15%.

In brief, these findings indicate the influence of oceanic air masses on aerosol mass concentration and composition. Further details will be presented.

How to cite: M. Kommula, S., panda, U., Sharma, A., S. Raj, S., Reyes villegas, E., D. Allan, J., Pöhlker, M., Krishna R., R., Liu, P., Pöschl, U., MCfiggans, G., Coe, H., and S. Gunthe, S.: Chemical Characteristics and Source Apportionment of Non-refractory PM1 from a Marine Urban Location, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12747, https://doi.org/10.5194/egusphere-egu2020-12747, 2020.

Condensation Particle Counters (CPCs) are the best-known and most frequently used tools for determining airborne particle number concentrations in the laboratory and a variety of real-life situations. While being a very established technique, current generations of CPCs have enhanced capabilities in terms of lower cut-off diameters, upper concentration limit as well as measurement quality features (e.g. pulse height monitoring). Knowledge of instrument accuracy is a primary matter in order to retrieve high quality data. In recent years, there has been an effort from measurement networks and within the EU’s standardization committee (CEN-TS 16976) to make ambient ultrafine particle number concentration data comparable. Long-term ambient monitoring requires frequent validation of instrument performance.

Inter-comparisons of multiple instruments against a reference instrument are important measures in order to secure long-term data quality. During inter-comparisons in the laboratory typically an aerosol of a certain type is generated and eventually classified in order to retrieve a monodisperse aerosol population. The aerosol needs to be equally distributed between the different instruments without being biased by sampling line losses.

This presentation will focus on inter-comparisons of CPCs being challenged with different types of aerosol. This includes lab-generated, highly monodisperse aerosol as well as ambient polydisperse aerosol. The accuracy of 10 units of a recently-introduced CPC (Model 3750, TSI Inc.) will be shown for ambient aerosol at data rates up to 50 Hz. All CPCs characterized agreed within 10% during the test, with concentrations of the ambient aerosol ranging from a few thousands up to 100,000 Particles/cm³.

In addition, results from inter-comparison studies using different butanol- and water-based CPC models that have been used for multiple years in different laboratories will be shown. Despite the different schedules for all instrument services and calibrations related to owners metrology requirement, these different CPC models demonstrated similar responses for the tested aerosols taking into account 10% uncertainties and are suitable candidates for reliable long-term operation in ambient ultrafine particle monitoring.

How to cite: Schmitt, S. H., Gendarmes, F., Tritscher, T., Zerrath, A., Krinke, T., and Bischof, O. F.: Concentration uncertainties in atmospheric aerosol measurement with Condensation Particle Counters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13059, https://doi.org/10.5194/egusphere-egu2020-13059, 2020.

Brown carbon (BrC) is generally emitted during coal combustion, biomass burning, and the formation of secondary organic aerosols. BrC is an exceptional type of organic compound that absorbs the incoming solar radiation efficiently at near-ultraviolet wavelengths and can influence the direct radiative forcing estimates. Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m above sea level) on the summit of Lulin Mountain in central Taiwan is the only high-altitude background station in the western Pacific region to study the impact of various long-range transported air pollutants. LABS usually receives the westerly winds coupled with biomass-burning emissions from peninsular Southeast Asia during the springtime. Aerosol measurements are carried out at LABS as a part of the Seven South East Asian Studies/Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment (7-SEAS/BASELInE) 2013 spring campaign. Light absorption coefficients are measured by the Aethalometer (AE 31, Magee Scientific, USA). Assuming a negligible contribution from dust, absorption solely due to BrC is estimated by subtracting the absorption of black carbon (BC) from total absorption. The relationships between BrC light absorption and carbonaceous fractions are investigated during the sampling period. The atmospheric radiative forcing due to BrC over the western Pacific region accounts for approximately 30% of that from BC. The detailed results will be presented.

How to cite: Pani, S. K., Lin, N.-H., Lee, C.-T., and Wang, S.-H.: Light absorption properties of brown carbon over the western Pacific region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15121, https://doi.org/10.5194/egusphere-egu2020-15121, 2020.

Mining activities are associated with dust emissions and increased contaminant levels in the environment, due to excavation, crushing and transportation of ore and the generation of a high amount of polluting wastes. Therefore, it is crucial to study the particulate matter in these areas to understand their impacts on nearby urban areas and populations (Csavina et al., 2012). Analysis PM₁₀ samples collected near the active mining area of Aljustrel (SW Portugal) allowed to do an individual characterization and to investigate the contaminants levels and aerosols sources. In Aljustrel, the exploitation of volcanogenic massive sulphides (VMS) deposits has been done since pre-Roman times, releasing great quantities of mine wastes, which have contaminated the soils (Candeias, et al. 2011). Now the exploitation is done underground, but even so, the ore processing plant releases dust, which is transported by wind to the village.

The PM₁₀ samples were collected in two points at the southeast of the ore processing plant. The sampling was done in two periods July 10-17 and November 1-10 of 2018. Two different techniques were used: SEM-EDX for the individual characterization and ICP-MS for the elemental concentration of 11 elements (Ca, Na, Fe, Mn, As, Cd, Cu, Sb, Pb, and Zn). PM₁₀ mass concentration observed was 20 to 47 µg m^-3 (July) and 4 to 23 µg m^-3 (November) which is lower than the limit of 50 μg m^-3 established in the European Directive (Directive 2008/50/CE of May 21). The individual characterization of 2006 particles by SEM-EDX shows the presence of oxides (17%) and sulphides (10%) in the aerosols, and the elements Na, Si, Fe, S, Al and Cu are those with the most representativeness in all the analyzed particles. The Principal Component Analysis (PCA) allowed to distinguish the main sources of aerosols. Five factors were extracted (72% of the total variance of the data): CP1 is defined by O, Al, Si and Fe, the geogenic elements; CP2 is defined by As and Pb, CP3 is defined by S, CP4 defined by Cu and Zn; and finally, the CP5 defined by Mn. These factors are related to the ore minerals. The ICP-MS results indicate that daily elemental concentration in the samples collected in July is higher than in those collected in November, for each element. The elements Fe, Cu, Zn, As, Cd, Sb, Pb have strong correlations (α = 0.05, r > 0.93) and are the main constituents of the ore minerals. Therefore, these elements will have an anthropogenic source. Comparing the concentration of some pollutes (As, Cd, and Pb) with their limits in the European legislation only As exceeds its limit in all samples.

This work was the first study about atmospheric aerosols developed in this area and shows a strong relationship between PM₁₀ analyzed and the ore exploited in Aljustrel, indicating implications in the quality of the air for the resident population. Even if some limits are not exceeded, the continuous exposition over many years is a potential hazard.

How to cite: Barroso, A., Mogo, S., Silva, M., Cachorro, V., and de Frutos, Á.: Atmospheric aerosol analysis close to the mining area of Aljustrel (SW of Portugal), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15354, https://doi.org/10.5194/egusphere-egu2020-15354, 2020.

Aerosol particles properties depend strongly on their particle size and they have significant effects on both, human health and environment. Nanometer sized particles possess special electrical, optical, and/or magnetic properties. This is one of the reasons which started the interest towards studying aerosol particles in the nanometer size range (Chen and Pui, 1995). The most efficient tool for determining the size of aerosol particle in the sub-micrometer and nanometer range is the differential mobility analyzer (DMA). This popular tool has two coaxial cylindrical electrodes between of them a potential difference is applied and forces the charged polydisperse aerosol to migrate from one electrode to another. Only those particles which have an electrical mobility in a narrow range, the will pass through the classifier (Stolzenburg, 1988).   Classifying aerosols according to their electrical mobility dates back to the first half of the 20^th century and from that time plethora different DMAs have been build and their performances have been tested according to their transfer function and size resolution. One major limitation of classical DMAs is the time it takes to scan over the entire size range to get the size distribution of the aerosol. This is especially leading to the loss of information if the aerosol is changing its size and/or concentration rapidly. This happens for instance during new particle formation events, or also when the measurement takes place on fast moving platforms, such as cars, or airplanes.

The present work evaluates the performance of two different, newly developed DMA types, that aim towards overcoming this limitation. This is done by replacing the classic design of a single monodisperse outlet DMA to a multiple monodisperse outlet DMA. In our case the DMAs have three monodisperse outlets and are 3D-printed (namely, the 3MO-DMA) (Chen et al., 2007; Giamarelou et al., 2012; Barmpounis et al., 2016; Bezantakos et al., 2016). The 3MO-DMA is not only a fast response instrument able to sizing three different sizes ranges at the same time but also is a cost-effective and lightweight instrument suitable to get measurements not only ground based but also on Unmanned Aerial Vehicles or balloons.

How to cite: Lekaki, N., Costi, M., Biskos, G., and Maisser, A.: Miniaturized, Lightweight, Cost-effective and Fast Response Particle Classifier, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17298, https://doi.org/10.5194/egusphere-egu2020-17298, 2020.

Black carbon (BC) aerosols over the Indian subcontinent have been represented inadequately so-far in chemical transport models restricting the accurate assessment of BC-induced climate impacts. The divergence between simulated and measured BC concentration has specifically been reported to be large over the Indo-Gangetic Plain (IGP) during winter when a large BC burden is observed. In this study, we evaluate the BC transport simulations over the IGP in a high resolution (0.1º × 0.1º ) chemical transport model, CHIMERE. We examine the model efficiency to simulate the observed BC distribution executing five sets of simulation experiments: Constrained and bottomup (Smog, Pku, Edgar, Cmip) implementing respectively, the recently estimated India-based constrained BC emission and the latest bottom-up BC emissions (India-based: Smog-India, and global: Coupled Model Intercomparison Project phase 6 (CMIP6), Emission Database for Global Atmospheric Research-V4 (EDGAR-V4) and Peking University BC Inventory (PKU)). The mean BC emission flux over most of the IGP from the five emission datasets is considerably high (450–1000 kg km^-2 y^-1) with a relatively low divergence obtained for the eastern and upper-mideastern IGP. Evaluation of BC transport simulations shows that the spatial and temporal gradient in the simulated BC concentration from the Constrained was equivalent to that from the bottomup and also to that from observations. This indicates that the spatial and temporal patterns of BC concentration are consistently simulated by the model processes. However, the efficacy to simulate BC distribution is commendable for the estimates from Constrained for which the lowest normalised mean bias (NMB, < 20%) is obtained in comparison to that from the bottomup (37–52%). 75–100% of the observed all-day (daytime) mean BC concentration is simulated most of the times (>80% of the number of stations data) for Constrained, whereas, this being less frequent (<50%) for the Pku, Smog, Edgar and poor for Cmip. The BC-AOD (0.04–0.08) estimated from the Constrained is 20–50% higher than the Pku and Smog. Three main hotspot locations comprising of a large value of BC load are identified over the eastern, mideastern, and northern IGP. Assessment of the effect of BC burden on the wintertime radiative perturbation over the IGP shows that the presence of BC aerosols in the atmosphere enhances atmospheric heating by 2–3 times more compared to that considering atmosphere without BC. Also, a net warming at the top of the atmosphere (TOA) by 10–17 W m^-2 is noticed from the Constrained, with the largest value estimated in and around megacities (Kolkata and Delhi) that extends to the eastern coast. This value is higher by 10–20% than that from Cmip over the IGP and by 2–10% than that from Smog over Delhi and eastern part of the IGP.

How to cite: Ghosh, S., Verma, S., and Kuttippurath, J.: Evaluation of emission strength efficacy in simulating black carbon burden with CHIMERE: estimating wintertime radiative effect over Indo-Gangetic Plain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17436, https://doi.org/10.5194/egusphere-egu2020-17436, 2020.

Elemental Carbon (EC), Black Carbon (BC) and Organic Carbon (OC) contribute a large amount to atmospheric aerosols. Due to their significant influence on climate and health, a reliable measurement of these components is essential. Nevertheless, their correct determination is not trivial and results of different measurement techniques show differences by factors up to nine especially in the presence of Brown Carbon (BrC) (e.g. Reisinger et al., 2008; Hitzenberger et al., 2006; Wonaschuetz et al., 2009). EC and OC are usually measured with thermal-optical techniques: The sample is heated stepwise, first in an inert (He) atmosphere, then in an oxidizing (He+O₂) atmosphere. The darkening of the sample during the heating procedure is traced with a laser transmission/reflection signal. Based on the progress of this signal, the amount of pyrolyzed carbon is calculated and attributed to OC in the subsequent evaluation. Despite this optical correction, the pyrolyzation of OC can lead to uncertainties in the OC/EC split (Cheng et al., 2012). Especially Brown Carbon (BrC) and water soluble organic carbons (WSOC) have a high tendency to pyrolyze and therefore bias the OC/EC split. Moreover several metal salts in the atmospheric aerosol can influence the measurement process and enhance or suppress pyrolysis of OC (Wang et al., 2010). These highly complex chemical and physical reactions are not fully investigated yet but are essential for a profound understanding of the biases in thermal-optical measurement techniques. 

The aim of the present study was to investigate the structural reorganizations of the carbonaceous materials in atmospheric aerosol samples occurring during a thermal-optical heating procedure (EUSAAR2, Cavalli et al., 2010) and to set them in relation with several properties of the samples such as ionic composition, EC, OC, BC and BrC, as well as the air mass origins during sampling of the atmospheric aerosol samples.
The changes of the internal structure of the material during the heating procedure of an EC/OC analyzer (Sunset instruments) were analyzed with Raman spectroscopy, which is sensitive to C-C bonding types and to the degree of structural ordering within the sample (Ferrari and Robertson, 2000). Different types of restructuration behavior were defined depending on the temperature levels of the EUSAAR2 protocol where measurable structural changes occur. For all samples ion chromatography was performed with a Dionex Aquion system (Thermo Fisher), BrC and BC were analyzed with the Integrating Sphere method (Wonaschütz et al., 2009) and air mass back trajectories for the respective sampling days were calculated with HYSPLIT.

How to cite: Haller, T., Sommer, E., Steinkogler, T., Wonaschuetz, A., Kasper-Giebl, A., Grothe, H., and Hitzenberger, R.: Investigation of structural changes of 21 atmospheric aerosol samples during a thermal-optical measurement procedure (EUSAAR2) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17585, https://doi.org/10.5194/egusphere-egu2020-17585, 2020.

Introduction

Fog provides a significant medium for chemical reactions occurring in liquid phase. Fog droplets are relatively small (5 < r < 50 µm) hence the surface-to-volume ratio is large. Through the larger overall surface the absorption of inorganic and organic gases from different sources may be enhanced. Depending on the stability of fog, the chemical processes may have more time to take place in fog droplets. Also, ground based sources of solid aerosol particles and gases may be in direct connection with fog.

Inorganic and organic components may change the pH of fog droplets and significant amount of sulphate ion can be formed due to the oxidation (e.g. by hydrogen-peroxide and ozone) of dissolved sulphur-dioxide. At the same time there are some organic components, e.g. formaldehyde, which also react with the dissolved sulphur-dioxide but produces hydroxymethanesulfonic acid (HMSA), thus decreases the possibility of producing sulphate ion through oxidation. These competitive processes are important in understanding the formation of sulphate ion in solution. In addition, the liquid phase concentration of compounds and also the sulphate ion formation strongly depends on the size of the droplets. Physical and chemical processes in fog may have an impact on both the size distribution and solubility of solid aerosol particles.

Numerical model

A box model with detailed microphysics and chemistry scheme with moving bin boundaries was used to simulate the following processes in fog:

• (i) Formation of drops on hygroscopic aerosol particles (ammonium-sulphate). Fog is formed due to cooling rate -0.0001 K/s.
• (ii) Condensational growth of drops.
• (iii) Scavenging of aerosol particles by water drops due to Brownian motion and phoretic forces.
• (iv) Absorption and desorption of inorganic (CO₂, H₂O₂, O₃, NH₃, SO₂) and organic (HCHO, HCOOH, CH₃COOH) gases, dissociation, change of pH, sulphate formation (oxidation of S(IV) by hydrogen-peroxide and by ozone and reaction of formaldehyde with S(IV)).

Results

Significant amount of HMSA formed in drops due to the reaction of S(IV) with formaldehyde. Taking into account this reaction, the amount of S(VI) formed is decreased compared to the case when no formaldehyde was present. Formation of HMSA modifies the solubility of the solid aerosol residue after evaporation of drops.

How to cite: Schmeller, G. and Geresdi, I.: Numerical simulation of chemical reactions occurring in fog droplets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17815, https://doi.org/10.5194/egusphere-egu2020-17815, 2020.

Aliphatic dicarboxylic acids (DCA) are significant constituents of oxygenated organic aerosol. Laboratory studies indicated that the major heterogeneous oxidation product of aerosol-phase aliphatic DCAs was the corresponding hydroxy DCAs (hDCAs). In this work, we focused our field investigation on hydroxyl DCAs and report their ambient abundance in an urban environment, and their correlations with other measured aerosol species. Good correlations (R~0.5-0.9) were observed between DCAs and hDCAs, supporting the precursor-product relationships between the two as suggested by laboratory studies. Moderate to good correlations were also observed for DCAs/hDCAs with oxidant potential (O_x=O₃+NO₂) (R~0.5-0.9) and sulfate (R~0.2-0.8) in summer. O_x might act as a gas phase oxidant indicator, hinting hat gas phase oxidation might play a role in formation of hDCAs. The effect of estimated LWC and sulfate was examined and illustrated through the contour plots. It was found that the episodic formation of DCAs and hDCAs was more associated with high concentration of sulfate, suggesting commonality in their formation pathways. However, high hDCA was not always associated with high estimated LWC. Long range transport contribution might explain such an observation. More efforts are needed to understand the formation conditions and mechanisms for hydroxyl dicarboxylic acids.

How to cite: Cheng, Y. Y. and Yu, J. Z.: Field observation of hydroxy diacids in PM2.5 and insights into their formation from aliphatic diacids through heterogeneous oxidation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18131, https://doi.org/10.5194/egusphere-egu2020-18131, 2020.

Comprehensive atmospheric studies have demonstrated that carbonaceous aerosol is one of the main components of atmospheric particulate matter over Europe. Despite its significant role in atmospheric processes, the characteristic of carbonaceous particle sources and the contributions from modern and fossil sources in the Pannonian Basin are still less known. Using radiocarbon as a tracer, the ratio of modern (biological aerosol, wood burning etc.) and fossil (coal or oil burning, transportation) sources for an aerosol sample can unambiguously be determined but identification of exact sources is not possible. Considering other isotopic techniques, carbon stable isotope results can provide us such supplementary information that can be used in separating different large source clusters (e.g. burning of C3 type wood, coal burning or transportation). Different aerosol sources have well defined carbon stable isotope ranges, which can be used in source apportionment models. Nevertheless, these ranges often overlap each other, making the accurate source identification rather difficult. Combined radiocarbon and carbon stable isotope measurements can however help us to differentiate more precisely numerous modern or fossil sources.

In our study, the isotopic composition of carbon in the PM_2.5 atmospheric aerosol collected on weekly basis in Debrecen, Hungary was investigated. In doing so, the organic and elemental carbon content, the specific ¹⁴C content and the δ¹³C values of total carbon were measured using a Sunset OC/EC analyser, an accelerator mass spectrometer (AMS) and an EA/IRMS instrument, respectively. Based on our three-year long carbon stable isotope data of carbonaceous aerosol, relatively enriched δ¹³C results can be observed in each wintertime period, which are supposed by other authors to be related to the effect of coal combustion (mainly in heavily industrialised areas). Contrarily, radiocarbon measurements imply the dominance of modern sources for the same wintertime periods when the biological activity of vegetation is moderate. Consequently, according to our assumption, these values are caused by modern sources having more positive δ¹³C value such as biomass burning of residences. In contrast to single stable isotope or radiocarbon measurements our study sheds light on the importance of combined carbon isotopic investigations. The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’

How to cite: Major, I., Furu, E., Varga, T., Horváth, A., Futó, I., Gyökös, B., Kertész, Z., Jull, A. T., and Molnár, M.: Evaluation of combined radiocarbon and carbon stable isotope data of PM2.5 carbonaceous aerosol in Debrecen, Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18136, https://doi.org/10.5194/egusphere-egu2020-18136, 2020.

Formaldehyde (HCHO) is produced mainly via photochemical oxidation of volatile organic compounds as well as direct emissions mainly from combustion processes. HCHO has a high vapor pressure but as a result of the hydration of the aldehyde group, it has a Henry’s law constant that allows it to partition into cloud droplets. We present results of two different pathways through which HCHO may contribute to the mass of particulate matter: Formation of hydroxymethanesulfonate (HMS) from reaction of HCHO with dissolved sulfur dioxide (SO_2aq) and formation of sulfate by reaction of HCHO with hydrogen peroxide (H₂O₂) to form hydroxyl methyl hydroperoxide (HMHP), which in turn can oxidize SO_2aq to sulfate and reform HCHO. The former pathway contributes to both the carbon and sulfur component of particulate matter whereas the latter contributes to the sulfur particulate budget and suggests a catalytic role of formaldehyde.

We combine laboratory kinetics studies of these reactions with model simulations using GEOS-Chem. The model simulations are analyzed at regional and global scales under present day and simplified preindustrial conditions, in which all anthropogenic emissions are set to zero. The analysis suggests that, depending on conditions, these processes may have significant impact on the sulfur particulate matter budget, specifically the rate of particulate sulfur formation. The results also suggest that under conditions that favor HMS formation, HMS may be the most abundant single organic molecule contributing particulate matter carbon.

How to cite: Keutsch, F., Dovrou, E., and Bates, K.: Direct and catalytic contribution of formaldehyde to particulate matter?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18319, https://doi.org/10.5194/egusphere-egu2020-18319, 2020.

Concentration of air pollutants such as tropospheric ozone and aerosols are mainly affected by meteorological variables and emissions. East Asia has large amount of anthropogenic and natural air pollutant emissions and has been putting lots of efforts to improve air quality. In order to seek effective ways to mitigate future air pollution, it is essential to understand the current emissions and their impacts on air quality. Emission inventory is one of the key datasets required to understand air quality and find ways to improve it. Amounts and spatial-temporal distributions of emissions are, however, not easy to estimate due to their complicate nature, therefore introduce significant uncertainties.

In this study, we had developed an updated version of our Asian emissions inventory, named NIER/KU-CREATE (Comprehensive Regional Emissions inventory for Atmospheric Transport Experiment) in support of climate-air quality study. We first inter-compare multiple bottom-up inventories to understand discrepancies among the dataset(sectoral, spatial). We then inter-compare those bottom-up emissions to the satellite-based top-down emission estimates to understand uncertainties of the databases. The bottom-up emission inventories used for this study are: CREATE, MEIC(Multiresolution Emission Inventory for China), REAS (Regional Emission inventory in ASia), and ECLIPSE(Evaluating the Climate and Air Quality Impacts of Short-Lived Pollutants). The satellite-derived top-down emission inventory had been acquired from the DECSO (Daily Emission derived Constrained by Satellite Observations) algorithm data from the GlobEmissions website.

The analysis showed that some discrepancies, in terms of emission amounts, sectoral shares and spatial distribution patterns, exist among the datasets. We analyzed further to find out which parameters could affect more on those discrepancies. Co-analysis of top-down and bottom-up emissions inventory help us to evaluate emissions amount and spatial distribution. These analysis are helpful for the development of more consistent and reliable inventories with the aim of reducing the uncertainties in air quality study. More results of evaluation of emissions will be presented on site.     

Acknowledgements : This work was supported by National Institute of Environment Research (NIER-2019-03-02-005), Korea Environment Industry & Technology Institute(KEITI) through Public Technology Program based on Environmental Policy Program, funded by Korea Ministry of Environment(MOE)(2019000160007). This research was supported by the National Strategic Project-Fine particle of the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT(MSIT), the Ministry of Environment(ME), and the Ministry of Health and Welfare(MOHW) (NRF-2017M3D8A1092022).

How to cite: Kim, Y., Woo, J., Jang, Y., Park, M., Kim, B., Amann, M., Klimont, Z., Wagner, F., Schöpp, W., and Sander, R.: Evaluation of Air Pollutant Emission Inventories in East Asia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18338, https://doi.org/10.5194/egusphere-egu2020-18338, 2020.

Tropospheric deliquesced particles including haze particles are a complex multiphase and multi-component environment with simultaneously occurring multiphase chemical transformations. Such chemical processes are able to alter the chemical composition and the deduced physical aerosol properties. Deliquesced particles are characterized by concentrated non-ideal solutions (‘aerosol liquid water’ or ALW) that can affect the occurring multiphase chemical processing. The effects of such non-ideal solutions have generally not been adequately investigated by present complex multiphase chemistry models. Thus, the present study is aimed at investigating the impact of non-ideality on multiphase chemical processing. Therefore, simulations with a multiphase chemistry model (SPACCIM-SpactMod) including the CAPRAM chemical mechanism are performed for polluted and less polluted environmental conditions and different ALW conditions.

The present study shows that activity coefficients of inorganic ions are often below unity under deliquesced aerosol conditions, and that most uncharged organic compounds exhibit activity coefficient values around or even above unity. The model studies demonstrated that the inclusion of non-ideality considerably affects the multiphase chemical processing of transition metal ions (TMIs), key oxidants, and related chemical subsystems, e.g. organic chemistry. In detail, both the chemical formation and oxidation fluxes of Fe(II) are substantially lowered by a factor of 2.8 under polluted haze conditions compared to a case study without non-ideality treatment. The reduced Fe(II) processing in the polluted base case, including lowered chemical fluxes of the Fenton reaction (-70 %), results in a reduced processing of HO_x/HO_y. under deliquesced aerosol conditions. Therefore, higher multiphase H₂O₂ concentrations (by a factor of 3.1 larger) and lower aqueous-phase OH concentrations (by a factor of ≈ 4 lower) were modelled during aerosol conditions. For H₂O₂, the consideration of non-ideality increases S(VI) oxidation fluxes under aqueous aerosol conditions by 40 %. Moreover, the chemical fluxes of the OH radical are about 50 % lower in the non-ideal haze case. Accordingly, the consideration of non-ideality affects the chemical processing and the concentrations of organic compounds under deliquesced particle conditions in a compound-specific manner. For important organic carboxylic acids, e.g. glyoxylic acid and oxalic acid, the reduced radical oxidation budget under aqueous particle conditions leads to increased concentration levels. For oxalic acid, the present study demonstrates that the non-ideality treatment enables more realistic predictions of high oxalate concentrations observed under ambient highly polluted conditions. Furthermore, the simulations show that lower humidity conditions, i.e. more concentrated solutions, might promote higher oxalic acid concentration levels in aqueous aerosols due to differently affected formation and degradation processes. Overall, the performed studies demonstrate the crucial role of a detailed non-ideality treatment in multiphase models dealing with aqueous aerosol chemistry and the needs to further improve current model implementations.

How to cite: Wolke, R., Tilgner, A., Rusumdar, A. J., and Herrmann, H.: Modelling the non-ideal multiphase chemical processing in aqueous aerosol particles with SPACCIM-SpactMod , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18555, https://doi.org/10.5194/egusphere-egu2020-18555, 2020.

Collisions of molecules and clusters play a key role in determining the rate of atmospheric new particle formation and growth. Traditionally the statistics of these collisions are taken from kinetic gas theory assuming spherical noninteracting particles, which may significantly underestimate the collision coefficients for most atmospherically relevant molecules. Such systematic errors in predicted new particle formation rates will also affect large-scale climate models. We studied the statistics of collisions of sulfuric acid molecules in a vacuum using atomistic molecular dynamics simulations. We found that the effective collision cross section of the H2SO4 molecule, as described by an optimized potentials for liquid simulation (OPLS) all-atom force field, is significantly larger than the hard-sphere diameter assigned to the molecule based on the liquid density of sulfuric acid. As a consequence, the actual collision coefficient is enhanced by a factor of 2.2 at 300 K compared with kinetic gas theory. This enhancement factor obtained from atomistic simulation is consistent with the discrepancy observed between experimental formation rates of clusters containing sulfuric acid and calculated formation rates using hard-sphere kinetics. We find reasonable agreement with an enhancement factor calculated from the Langevin model of capture, based on the attractive part of the atomistic intermolecular potential of mean force.

How to cite: Halonen, R., Zapadinsky, E., Kurtén, T., Vehkamäki, H., and Reischl, B.: Rate enhancement in collisions of sulfuric acid molecules due to long-range intermolecular forces, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18959, https://doi.org/10.5194/egusphere-egu2020-18959, 2020.

Fine particles can reach deeply into various tracts in the human body, causing adverse health effects. In addition, particulate matter affects earth energy balance directly, scattering solar radiation, and indirectly, forming clouds and changing cloud properties. In these respects, understanding the variations of aerosol concentrations in each mode of aerosol size distributions and the factors affecting those variations, is important.

In this study, we attempted to separate each mode from the aerosol size distributions obtained from long-term observations with scanning mobility particle sizer (SMPS) (December 2007 to October 2018) in Jeju Island (Gosan, national background concentration network, 33.17˚N, 126.12˚E).

The particle number size distributions (54 channels, from 10.4 nm to 469.8 nm) were separated into three modes using a fitting method based on the multiple lognormal distribution function. We then attempted to examine how these modes of particles have changed in time, and what factors (air trajectories, meteorology, other pollutants, and others) were related to the variations in each mode. We also calculated the deposition fractions of inhaled aerosols in each human respiratory tract from the observed size distributions using the International Commission on Radiological Protection (ICRP) deposition model, and we examined how these deposition fractions vary in different air quality conditions.

More details in the discussion concerning temporal variations in aerosol size distributions, the factors affecting those variations, and variations in deposition fractions in the human body are presented.

Keywords: aerosol, size distribution, deposition fraction, lognormal distribution mode.

How to cite: An, C., Kim, S., and Choi, W.: Variations in aerosol size distributions and deposition fractions in human body based on long-term observations (2007 to 2018), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19389, https://doi.org/10.5194/egusphere-egu2020-19389, 2020.

East Asia has suffered from severe air pollution, particularly concerning particulate matter less than 2.5 µm in diameter (PM_2.5). Although air quality in Korea has been gradually improved with respect to annual mean PM_2.5 and PM₁₀ concentrations, high PM pollution events have been worse in their peak concentrations and durations.

In this study, we attempted to find statistically how the characteristics of PM_2.5 pollution over Korea have changed with a focus on temporal and spatial variations. Hourly PM_2.5 concentration data were obtained from 374 air quality monitoring stations (AQMS) throughout the country from January 2015 to June 2019. With obtained air quality data, we selected high PM pollution periods based on the national air pollution standard, and examined how the magnitudes and durations of high PM pollution events, as well as the background concentrations, have changed since 2015 over Korea. Additionally, we applied the time-lag correlation method to see how the onsets of PM_2.5 pollution events differ in space and how high PM_2.5 spread out in time. We also applied the coefficient of divergence (COD) to countrywide datasets of PM_2.5 as a measure of spatial heterogeneity of PM_2.5 distributions.

Although annual mean concentrations of PM_2.5 tend to decline from 2015 to 2018, the peak concentrations and durations for severe PM_2.5 pollution events tend to increase in most regions of Korea for the periods of January to April. We also categorized the characteristic distribution patterns in severe PM events combining the time-lag correlation and COD results. In most pollution events, the time-lag distributions showed clear delay patterns of pollution events from the reference area (Seoul). Additionally, COD results showed a clear heterogeneity of PM_2.5 distributions as the distance from the reference area increases along the time-lag. Although spatial correlations and COD results of PM_2.5 concentrations between the reference area and other regions indicated heterogeneous distributions, time-lag corrected COD values imply that PM_2.5 over much wider regions of Korea are homogeneously distributed in both magnitudes and temporal variations. The R² values were significantly improved after time-lag correction. These results imply that high PM_2.5 events are significantly affected by synoptic weather conditions over most regions of Korea; thus, potential modification of synoptic weather patterns in East Asia caused by climate change can be an important factor for variations in high PM_2.5 pollution events.

Keywords: coefficient of divergence (COD), PM_2.5 pollution events, spatial heterogeneity of PM distributions, pattern analysis.

How to cite: Han, S., Park, Y., and Choi, W.: Spatiotemporal variability patterns of PM2.5 in severe pollution events based on a large dataset from air quality monitoring stations over South Korea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19493, https://doi.org/10.5194/egusphere-egu2020-19493, 2020.

How to cite: Neefjes, I., Zanca, T., Kubecka, J., Zapadinsky, E., Passananti, M., Kurtén, T., and Vehkamäki, H.: A process model to predict the faith of clusters in CI-APi-TOF mass spectrometers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20589, https://doi.org/10.5194/egusphere-egu2020-20589, 2020.

During the blooming season of trees, pollen is an important component of the atmospheric aerosol, even in urban areas. Wind pollinated plants such as early flowering trees (e.g. birch, alder) release pollen grains in extremely large quantities. Once in the atmosphere pollen can impact human health and cloud formation (Schäppi et al. 1999, Pummer et al. 2012, Steiner et al. 2015). Intact pollen grains are rather large with geometrical diameters from 10-100 μm and therefore have short residence times in the atmosphere. However, it is known that under certain conditions (high humidity and after germination) pollen grains release cytoplasmic material including starch granules from their interior, commonly referred to as subpollen particles (SPP). Studies have shown that the cytoplasmic material contains cloud active substances and allergens (Steiner et al. 2015, Pummer et al. 2012, Basci et al. 2006). How and if this material becomes airborne and whether it distributes in the atmosphere is still an open question. Motivated by this question we took a detailed look at the particles shed from blooming catkins.

In this study freshly harvested branches with flowering catkins of different trees were put in an aerosol chamber. An Aerodynamic Particle Sizer (TSI Spectrometer 3321; 0.5 – 20 μm) and a Cascade Impactor (Sioutas; 2.5 μm, 1.0 μm, 0.50 μm, 0.25 μm) were attached to the chamber to sample the released aerosol. The catkins were agitated with puffs of clean air to simulate wind. The aerodynamic diameters of the released particles were recorded and the filters of the impactor were analyzed with a Scanning Electron Microscope and a light microscope. We find that not only large pollen grains are released but also smaller particles. Up to 50% of all released particles were in the size range from (0.5 – 5 μm). Additionally, we find that the aerodynamic diameter of pollen grains is in general smaller than their geometrical diameter. For instance, the aerodynamic diameter of pollen grains from birch is 30-70% smaller than the geometrical diameter.

References:
Schäppi, G. F.; Taylor, P. E.; Pain, M. C.; Cameron, P. A.; Dent, A. W.; Staff, I. A. & Suphioglu, C.; Concentrations of major grass group 5 allergens in pollen grains and atmospheric particles: implications for hay fever and allergic asthma sufferers sensitized to grass pollen allergens.; Clinical and experimental allergy: journal of the British Society for Allergy and Clinical Immunology, 1999, 29, 633-641
Pummer, B. G.; Bauer, H.; Bernardi, J.; Bleicher, S. & Grothe, H.; Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen; Atmospheric Chemistry and Physics, Copernicus GmbH, 2012, 12, 2541-2550
Steiner, A. L.; Brooks, S. D.; Deng, C.; Thornton, D. C. O.; Pendleton, M. W. & Bryant, V.; Pollen as atmospheric cloud condensation nuclei; Geophysical research letters, Wiley Online Library, 2015, 42, 3596-3602
Bacsi, A.; Choudhury, B. K.; Dharajiya, N.; Sur, S. & Boldogh, I.; Subpollen particles: carriers of allergenic proteins and oxidases; Journal of Allergy and Clinical Immunology, Elsevier, 2006 , 118 , 844-850

How to cite: Gratzl, J., Seifried, T. M., Bieber, P., Grothe, H., and Burkart, J.: Blooming trees as a source of fine (< 5μm) aerosol particles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21035, https://doi.org/10.5194/egusphere-egu2020-21035, 2020.

The earth observing satellites including the low earth orbit (LEO) and geostationary orbit (GEO) platforms have been provided the geophysical data. Spectral radiances measured by a satellite-borne sensor are sensitive to both atmospheric transmission and surface reflection. These volumetric data were used to retrieve atmospheric transmission and surface reflection which can be useful to derive surface reflectance (SR) and aerosol optical thickness (AOT). Based on the extensive radiative transfer simulations with the LEO satellite’s operational atmospheric products, it is demonstrated that the use of the combined LEO and GEO satellite measurements allows for timely retrieval of SR and AOT at a reasonable accuracy. The method for both the Geostationary Ocean Color Imager (GOCI) and the Landsat-8 Operational Land Imager (OLI) data. After the spatial and temporal collocations between two different orbit data, the atmospheric correction of both satellite’s spectral reflectances showed that the averaged changes of reflectance in 10% to 30%. Moreover, comparisons with the other operational products of SR and AOT such as the ground-based Aerosol Robotic Network (AERONET) showed retrieval error of within ±5.6% SR and ±9.8% AOT. Combining the LEO and GEO satellite data are effective method for the atmospheric correction and geophysical parameter retrieval. Further work will be applied to the next generation geostationary satellites, namely the Geostationary Earth Orbit Korea Multi-Purpose Satellite (GEO-KOMPSAT-2A and -2B) platforms.

Acknowledgement
This subject is supported by the Korea Aerospace Research Institute (KARI) (FR19920W05) and Korea Ministry of Environment (MOE) as "Public Technology Program based on Environmental Policy (2017000160003).

How to cite: Lee, K.-H. and Yum, J.-M.: Aerosol remote sensing from the integrated LEO and GEO satellite observation data by determination of atmospheric transmission and surface reflection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21280, https://doi.org/10.5194/egusphere-egu2020-21280, 2020.

The ozonolysis of oleic acid on aerosol particles has been extensively studied in the past and is often used as a benchmark reaction for the study of organic particle oxidation. However, to date, no single kinetic model has reconciled the vastly differing reactive uptake coefficients reported in the literature that were obtained at different oxidant concentrations, particle sizes and with various commonly used laboratory setups (single-particle trap, aerosol flow tube, and environmental chamber). We combine the kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB, Shiraiwa et al. 2012) with the Monte Carlo Genetic Algorithm (MCGA, Berkemeier et al. 2017) to simultaneously describe nine experimental data sets with a single set of kinetic parameters. The KM-SUB model treats chemistry and mass transport of reactants and products in the gas and particle phases explicitly, based on molecular-level chemical and physical properties. The MCGA algorithm is a global optimization routine that aids in unbiased determination of these model parameters and can be used to assess parameter uncertainty. This methodology enables us to derive information from laboratory experiments using a “big data approach” by accounting for a large amount of data at the same time.

We show that a simple reaction mechanism including the surface and bulk ozonolysis of oleic acid only allows for the reconciliation of some of the data sets. An accurate description of the entire reaction system can only be accomplished if secondary chemistry is considered and present an extended reaction mechanism including reactive oxygen intermediates. The presence of reactive oxygen species on surfaces of particulate matter might play an important role in understanding aerosol surface phenomena, organic aerosol evolution, and their health effects.

References

Berkemeier, T. et al.: Technical note: Monte Carlo genetic algorithm (MCGA) for model analysis of multiphase chemical kinetics to determine transport and reaction rate coefficients using multiple experimental data sets, Atmos. Chem. Phys., 17, 8021-8029, 2017.

Shiraiwa, M., Pfrang, C., and Pöschl, U.: Kinetic multi-layer model of aerosol surface and bulk chemistry (KM-SUB): the influence of interfacial transport and bulk diffusion on the oxidation of oleic acid by ozone, Atmos. Chem. Phys., 10, 3673-3691, 2010.

How to cite: Mattei, C., Shiraiwa, M., Pöschl, U., and Berkemeier, T.: Reconciling multiphase reactivity of oleic acid with ozone using a kinetic flux model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21531, https://doi.org/10.5194/egusphere-egu2020-21531, 2020.

Atmospheric new particle formation and successive cluster growth to aerosol particles is an important field of research, in particular due to climate change phenomena and air quality monitoring. Recent developments in the instrumentation have enabled quantification of ionic clusters formed in the gas phase at the first steps of particle formation under atmospherically relevant mixing ratios. However, electrically neutral clusters are prevalent in atmospheric conditions, and thus must be charged prior to detection by mass spectrometer. The charging process can lead to cluster fragmentation and thus alter the measured cluster composition.

Even when the cluster composition can be measured directly, this does not quantify individual cluster-level properties, such as cluster collision and evaporation rates. Collision rates contain relatively small uncertainties in comparison to evaporation rates, which are computed using detailed balance assumption together with the free energies of cluster formation, which can in turn be obtained from Quantum chemistry (QC) methods. As evaporation rates depend exponentially on the free energies, even difference by several kcal/mol between different QC methods results in orders of magnitude differences in evaporation rates.

On the other hand, in spite of the error margins associated with the evaporation rates, simulations of cluster populations, which incorporate collision and evaporation rates as free parameters (such as Becker-Döring models), have demonstrated good qualitative agreement with experimental data. The Becker-Döring equations are a system of Ordinary Differential equations (ODE) which account for cluster birth and death processes, as well as external sinks and sources. In mathematical terms, prediction of cluster concentrations using kinetic simulations with given cluster collision and evaporation rates is called a forward problem.

In the present study, we focus on the so-called inverse problem of how to derive the evaporation rates and thermodynamic data (enthalpy change and entropy change due to addition or removal of molecule) from available measurements, rather than on the forward problem. We do this by Delayed Rejection Adaptive Monte Carlo (DRAM) method for the system containing sulfuric acid and ammonia with the maximal size of the pentamer. Initially, we tested the method on the synthetic data created from Atmospheric Cluster Dynamic Code (ACDC) simulations. By so doing, we identify the combination of fitted parameters and concentration measurements, which leads to the best identification of the evaporation rates. Additionally, we demonstrated that the temperature-dependent data yield better estimates of the evaporation rates as compared to the time-dependent data measured before the system has reached the steady state.

Next, we apply the technique to improve the identification of the evaporation rates from CLOUD chamber data, which contain cluster concentrations and new particle formation rates measured at different temperatures and a wide range of atmospherically relevant sulfuric acid and ammonia concentrations. As a result, we were able to obtain the probability density functions (PDFs) that show small standard variations for thermodynamic data. By using the values from the PDFs as parameters in the ACDC model, we achieve a fair agreement with the measured NPFs and cluster concentrations for a wide range of temperatures.

How to cite: Shcherbacheva, A., Helin, T., Haario, H., and Vehkamäki, H.: Improved identification of evaporation rates and thermodynamic data by Monte-Carlo method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21614, https://doi.org/10.5194/egusphere-egu2020-21614, 2020.

Size resolved data of chemical species carries a lot of latent information about the sources and atmospheric processes which lead to their formation and growth. Source apportionment techniques on organic or inorganic aerosols provide a fair amount of information about the sources but this analysis only provides a partial picture owing to the complicated nature of the ambient aerosols which may contain both, organic as well as inorganic particulate matter. Traditionally, potential emission sources are distinguished by either the organic or inorganic tracers present in ambient aerosol, but recently several studies have performed PMF on both the species (Sun et al, 2012). However, it tells more about the final transformed products which could be formed from different pathways but not much about the transformation pathways. Insights about the source and the atmospheric processes involved can be derived from the analysis of size-resolved data of the ambient aerosol. PMF on Size-resolved information helps us to narrow down the possible pathways of the transformed products.

However, there is very limited literature available to help us understand more about size-resolved bulk particulate matter. In this manuscript, a novel approach to perform Positive Matrix Factorization (PMF) on real-time size-resolved Unit Mass Resolution (UMR) data from Aerosol Mass Spectrometer (AMS) is presented. Both size- and time-resolved PMF is performed on non-refractory particle composition (organic & inorganic) on the UMR PTOF data of two sites in one of the most polluted cities in the world. The sampling through Long Time of flight mass spectrometer (LToF-AMS) was carried out at Indian Institute of Technology, Delhi which is located in Hauz Khaz area, at the heart of Delhi NCR, whereas parallel sampling through High-resolution Time of flight aerosol mass spectrometer (HR-ToF-AMS) was carried out at Manav Rachna University which is located in Faridabad within Delhi NCR at a downwind location. PMF was performed on the data by using Multi-linear Engine (ME-2) on PMF model by SoFi (Source Finder) tool. A seven-factor solution was chosen based on the factor profiles, time series, diurnals and correlation with the external factors obtained by supplementary instruments. The size-resolved spectra of the species at an individual site was studied and the difference between the sites was compared.

How to cite: Mishra, S., Tripathi, S., Thamban, N., Lalchandani, V., Kumar, V., Rai, P., Tiwari, S., Ganguly, D., Bhattu, D., Slowik, J., and Prevot, A.: Source apportionment of time- and size-resolved particulate matter over two sites in New Delhi & NCR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21640, https://doi.org/10.5194/egusphere-egu2020-21640, 2020.

Atmospheric particulate matter has adverse effects on human health, and causes over 4 million deaths per year globally. New Delhi was ranked as world’s most polluted megacity with annual average PM_2.5 concentration of ~140 ug.m^-3. Thus, real time chemical characterization of fine particulate matter and identification of its sources is important for developing cost effective mitigation policies.

Highly time resolved real-time chemical composition of PM_2.5 was measured using Long-Time of Flight-Aerosol Mass Spectrometer (L-ToF-AMS) at Indian Institute of Technology Delhi and Time of Flight-Aerosol Chemical Speciation Monitor (ToF-ACSM) at Indian Institute of Tropical Meteorology, Delhi, and PM₁ using High Resolution-Time of Flight-Aerosol Mass Spectrometer (HR-ToF-AMS) at Manav Rachna International University, Faridabad, Haryana located ~40 km downwind of Delhi during Jan-March, 2018. Black carbon concentration was measured using Aethalometer at all three sites. Unit mass resolution (UMR) and high resolution (HR) data analysis were performed on AMS and ACSM mass spectra to calculate organics, nitrate, sulfate and chloride concentrations. Positive Matrix Factorization (PMF) (Paatero and Tapper, 1994) of organic mass spectra was performed by applying multilinear engine (ME-2) algorithm using Sofi (Source finder) for identifying sources of OA.

How to cite: Tripathi, S., Lalchandani, V., Kumar, V., Tobler, A., Thamban, N., Mishra, S., Slowik, J., Bhattu, D., Ganguly, D., Tiwari, S., and Prevot, A.: Chemical characterization of fine particulate matter, and source apportionment of organic aerosol at three sites in New Delhi, India, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21813, https://doi.org/10.5194/egusphere-egu2020-21813, 2020.