AS3.1

Spectrometers are powerful instruments to detect atmospheric aerosols, especially on satellites since they allow measurements at a global scale and over different spectral ranges with high spectral resolution. However, to fully exploit their capabilities and to link optical properties, chemical composition and mass concentration, it is essential to have reference optical properties of various particles and mainly the complex refractive indices (CRI). The CRI of a natural aerosol source can be determined from a real sample of it or applying the effective medium approximation using the CRI of the pure compounds present in the natural sample. But in that case, it is necessary to know the mass fraction of each individual compound and above all their CRI. Nevertheless, the literature and CRI databases provide only reflectance measurements on bulk materials or pressed pellets and over a limited wavelength range (Querry et al., 1987).

In the present work, dust from the Gobi desert is studied as it is the second most active dust source, after the Sahara desert, in terms of mass emissions (Querol et al., 2019). For that extinction spectra have been recorded for natural Gobi dust sample and for its major compounds (Illite, Calcite and Quartz). Particles as a powder in a vessel are generated thanks to a magnetic stirring and a flow of nitrogen (Hubert et al., 2017). The continuous flow of aerosols is directed into a 10-meters multipass cell fitted to a Fourier transform infrared spectrometer and a 1-meter singlepass cell within a UV-Visible spectrometer which cover a continuous spectral range from 650 cm^-1 to 40000 cm^-1. Moreover, at the exit of the spectrometers the size distribution is recorded by an aerodynamic particle sizer and a scanning mobility particle sizer which allow to measure size particles from 14 nm to 20 µm. An inversion algorithm is carried out using experimental extinction spectra and the size distribution as input data (Herbin et al., 2017). Applying the Mie theory and the single subtractive Kramers-Kröning integral, the real and the imaginary part of the CRI are retrieved at each wavelength with an optimal estimation method.

For the first time, CRI of Illite has been retrieved with a high spectral resolution (1 cm^-1) and over a wide spectral range for suspended particles. For calcite and quartz particles, the crystalline phase has to be considered by introducing the ordinary and extraordinary indices. These pure compound sets of CRI will be used for testing effective medium approximation on Gobi dust for which effective CRI have been also retrieved.

How to cite: Deschutter, L., Herbin, H., and Petitprez, D.: Optical properties of Gobi dust and its pure compounds: experimental extinction spectra and complex refractive indices determination., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2115, https://doi.org/10.5194/egusphere-egu21-2115, 2021.

The photolysis module in Environment and Climate Change Canada’s on-line chemical transport model GEM-MACH (GEM: Global Environmental Multi-scale – MACH: Modelling Air quality and Chemistry) was improved by using the on-line chemical composition and size-resolved representation of atmospheric aerosols in GEM-MACH to calculate the attenuation of radiation in the photolysis module.

We coupled both the GEM-MACH aerosol module and the MESSy-JVAL (Modular Earth Sub-Model System) photolysis routine through the use of the on-line aerosol modeled data and a new Mie lookup table for the model-generated extinction efficiency, absorption and scattering cross sections of each aerosol. The new algorithm applies a lensing correction factor to the black carbon absorption efficiency (core-shell parametrization) and calculates the scattering and absorption optical depth and asymmetry factor of black carbon, sea-salt, dust and other internally mixed components.

In order to evaluate the effects of these modifications on the performance of the GEM-MACH model, a series of simulations with the updated version of MESSy-JVAL and wildfire emission inputs from the Canadian Forest Fire Emissions Prediction System (CFFEPS) were carried out, and the model aerosol optical depth (AOD) output was compared to the previous version of MESSy-JVAL, satellite data, ground-based measurements, and re-analysis products. The comparison of the updated version of MESSy-JVAL with the previous version showed significant improvements in the model performance with the implementation of the new photolysis module and adopting the online interactive aerosol concentrations in GEM-MACH.

How to cite: Majdzadeh, M., Stroud, C., Sioris, C., Makar, P., Akingunola, A., McLinden, C., Zhao, X., Moran, M., Abboud, I., and Chen, J.: Impact of Interactive Aerosol Feedbacks on Photolysis Rates and Air Quality for Urban and Industrial Areas in Canada using the GEM-MACH Air Quality Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3367, https://doi.org/10.5194/egusphere-egu21-3367, 2021.

Aerosol particles are ubiquitous in the atmosphere and play an important role for air quality and Earth’s climate. Primary organic aerosol (POA), secondary organic aerosol (SOA), and secondary inorganic aerosol (SIA) constitute a significant mass fraction of these particles. POA, SOA, and SIA can become internally mixed within the same particle though different processes such as coagulation, gas–particle partitioning. To predict the role of these internally mixed particles in climate and air quality information on their phase behaviour is needed, i.e. information on the number and type of phases present within these particles. As an example, a particle with a single homogeneous liquid phase can have different radiative properties, reaction rates, uptake kinetics, and potential to change cloud microphysical properties by activating into a cloud droplet, compared to a particle with multiple liquid or solid phases.

In the current study we used Nile red, a solvatochromic dye, and fluorescence microscopy in order to determine the phase behaviour of POA+SOA+SIA particles. Squalane was used as a proxy of POA, ammonium sulfate was used as SIA and 1 of 23 different oxidized organic molecules were used as proxies of SOA. We demonstrate that three liquid phases often coexist within individual particles. We find that the phase behaviour strongly depends on the oxygen-to-carbon ratio of the SOA proxies. Experiments with SOA generated by dark ozonolysis of α-pinene in an environmental chamber are consistent with these observations. We also used thermodynamic and kinetic modelling to investigate the atmospheric implications of our experimental results.

How to cite: Mahrt, F., Huang, Y., Xu, S., Shiraiwa, M., Zuend, A., and Bertram, A.: Coexistence of three liquid phases in atmospheric aerosol particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3694, https://doi.org/10.5194/egusphere-egu21-3694, 2021.

Validation opportunities for model data and satellite observations in the short-wave infra-red spectral range for climate monitoring are still sparse above the oceans. Klappenbach et al. (2015) and Knapp et al. (2020) developed a ship-borne setup of a Fourier-transform spectrometer (EM27/SUN FTS) for direct sunlight observations on mobile platforms such as ships or pick-ups. The housing withstands oceanic on-deck-conditions and is equipped with a custom-built fast solar tracker. Knapp et al. (2020) tested the system on a ship cruise from Vancouver, Canada to Singapore for a five-week period in 2019, during which the instrument performed reliably. The tracker provided a pointing precision of better than 0.05° for 79% of the time. The precision of atmospheric total column densities retrieved from the FTS direct sunlight spectra was found to be 0.24ppm for carbon dioxide (CO₂), 1.1ppb for methane (CH₄), and 0.75ppb for carbon monoxide (CO).

Our ultimate goal is to develop the setup towards autonomous operations on ships to routinely collect validation data for CO₂, CH₄, and CO column densities above the world's oceans. Therefore, we further improved on the FTS box. Most prominent is a simplification of the tracking algorithm from two-dimensional mapping to two one-dimensional functions, moving a 185° fisheye camera onto the tracking rotation stage, and a change to more reliable embedded computers. Those modifications allow for sun tracking down to a solar zenith angle of 75° and increase robustness against mechanical misalignments between tracker and camera. A test campaign was conducted in the vicinity of a local coal power plant in Mannheim, Germany by mounting the FTS box on a pick-up and driving a stop-and-go pattern perpendicular to the plume direction. To this purpose, a 24 V battery powering mode was implemented.

We plan another deployment of the instrument on the Japanese research vessel Mirai in February 2021. The campaign is conducted in cooperation with the Japanese National Institute for Environmental Studies (NIES) in the western North Pacific. Such routine validation opportunities of atmospheric CO₂, CH₄, and CO column densities would be a valuable asset for global climate monitoring.

Knapp, M., Kleinschek, R., Hase, F., Agustí-Panareda, A., Inness, A., Barré, J., Landgraf, J., Borsdorff, T., Kinne, S., and Butz, A.: Ship-borne measurements of XCO2, XCH4, and XCO above the Pacific Ocean and comparison to CAMS atmospheric analyses andS5P/TROPOMI, Earth System Science Data Discussions, 2020, 1–20, https://doi.org/10.5194/essd-2020-132, https://essd.copernicus.org/preprints/essd-2020-132/, 2020.

Klappenbach, F., Bertleff, M., Kostinek, J., Hase, F., Blumenstock, T., Agusti-Panareda, A., Razinger, M., and Butz, A.: Accurate mobileremote sensing of XCO2 and XCH4 latitudinal transects from aboard a research vessel, Atmospheric Measurement Techniques, 8,5023–5038, https://doi.org/10.5194/amt-8-5023-2015, 2015.

How to cite: Hanft, V., Kleinschek, R., Knapp, M., Müller, A., Frey, M., Tanimoto, H., Morino, I., Hase, F., Holzbeck, P., and Butz, A.: Towards An Automated Ship-Borne Fourier-Transform Spectrometer As a Validation Opportunity For Atmospheric CO2, CH4, And CO Column Densities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4030, https://doi.org/10.5194/egusphere-egu21-4030, 2021.

Aerosol acidity largely regulates the chemistry of atmospheric particles, and resolving the drivers of aerosol pH is key to understanding their environmental effects. We find that an individual buffering agent can adopt different buffer pH values in aerosols and that aerosol pH levels in populated continental regions are widely buffered by the conjugate acid-base pair NH₄⁺/NH₃ (ammonium/ammonia). We propose a multiphase buffer theory (Zheng et al., 2020, Science) to explain these large shifts of buffer pH, and we show that aerosol water content and mass concentration play a more important role in determining aerosol pH in ammonia-buffered regions than variations in particle chemical composition. Our results imply that aerosol pH and atmospheric multiphase chemistry are strongly affected by the pervasive human influence on ammonia emissions and the nitrogen cycle in the Anthropocene.

References:

Zheng, G., Su, H.*, Wang, S., Andreae, M. O., Pöschl, U., and Cheng, Y.*: Multiphase buffer theory explains contrasts in atmospheric aerosol acidity, Science, 369, 1374-1377, 2020.

How to cite: Zheng, G., Su, H., Wang, S., Andreae, M., Pöschl, U., and Cheng, Y.: Multiphase buffer theory explains contrasts in atmospheric aerosol acidity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4936, https://doi.org/10.5194/egusphere-egu21-4936, 2021.

Transport of organic trace gases by deep convective clouds plays an important role for new particle formation (NPF) and particle growth in the upper atmosphere. Isoprene accounts for a major fraction of the global volatile organic vapor emissions and a significant fraction is emitted in the Amazon. We examined transport and chemical processing of isoprene and its oxidation products in a deep convective cloud over the Amazon using a box model. Trajectories of individual air parcels of the cloud derived from a large eddy simulation are used as input to the model. Our results show that there exist two main pathways for NPF from isoprene associated with deep convection. The first one is when the gas transport occurs through a cloud with low lightning activity and with efficient gas uptake of low-volatile oxidation products by ice particles. Some of the isoprene will reach the cloud outflow where it is further aged and produces low volatile species capable of forming and growing new particles. The second way is via transport through clouds with high lightning activity and with low gas uptake by ice. For this case, low volatile oxidation products will reach the immediate outflow in concentrations close to the values observed in the boundary layer. The efficiency of gas condensation on ice particles is still uncertain and further research in this direction is needed.

How to cite: Bardakov, R., Thornton, J., Riipinen, I., Krejci, R., and Ekman, A.: Transport of isoprene and its oxidation products by deep convective clouds in the Amazon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5755, https://doi.org/10.5194/egusphere-egu21-5755, 2021.

The rapid changes in the pattern of atmospheric warming over the Himalayas, along with severe degradation of Himalayan glaciers in recent years suggest the inevitability of accurate source characterization and quantification of the impact of aerosols on the Himalayan atmosphere and snow. In this regard, extensive study of the chemical compositions of aerosols at two distinct regions, Himansh (32.4^ᴼN, 77.6^ᴼE, ~ 4080 m a.s.l) and Lachung (27.4^ᴼN, 88.4^ᴼE, ~ 2700 m a.s.l), elucidates distinct signatures of the sources and types of aerosols prevailing over the western and eastern parts of Himalayas. The mass-mixing ratios of water-soluble (Na⁺, NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Cl-, SO₄^2-, NO₃^-, MSA^-, C₂O₄^2-), carbonaceous (EC, OC, WSOC) and selected elemental (Al, Fe, Cu, Cr, Ti) species depicted significant abundance of mineral dust aerosols (~ 67%), along with a significant contribution of carbonaceous aerosols (~ 9%) during summer to autumn (August-October) over the western Himalayan site. On the other hand, the eastern Himalayan site is found to be dominant of OC (~ 53% in winter) followed by SO₄^2- (as high as 37% in spring) and EC (8-12%) during August to February. However, OC/EC and WSOC/OC ratios showed significantly higher values over both the sites (~ 12.5, and 0.56 at Himansh; ~ 5.7 and ~ 0.74 at Lachung) indicating the secondary formation of organic aerosols via chemical aging over both the sites. The enrichment factors estimated from the concentrations of trace elements over the western Himalayan site revealed the influence of anthropogenic source contribution from the regional hot-spots of Indo-Gangetic Plains, in addition to that of west Asia and the Middle East countries. On the other hand, the source apportionment of aerosols (based on positive matrix factorization - PMF model) over the eastern Himalayas demonstrated the biomass-burning aerosols (25.94%), secondary formation of aerosols via chemical aging (15.94%), vehicular and industrial emissions (20.54%), primary emission sources associated with mineral dust sources (22.28%) and aged secondary aerosols (15.31%) as the major sources of aerosols. Due to abundant anthropogenic source impacts at the eastern Himalayan site, the atmospheric forcing is most elevated in winter (13.4 ± 4.4 Wm^-2), which is more than two times the average values seen at the western Himalayan region during the study period. The heavily polluted eastern part of the IGP is a potential anthropogenic source region contributing to the aerosol loading at the eastern Himalayas. These observations have far-reaching implications in view of the role of aerosols on regional radiative balance and their impact on snow/glacier coverage.

How to cite: Bs, A., Gogoi, M., Hegde, P., and Babu, S.: Contrasting signatures of the sources and types of aerosols in the western and eastern Himalayas: Radiative implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5916, https://doi.org/10.5194/egusphere-egu21-5916, 2021.

Aerosols play a key role in radiative transfer processes at the Earth’s atmosphere. The complex interactions between aerosols and solar radiation cannot be easily modeled, and thus, aerosols constitute a major uncertainty factor in radiative transfer simulations. Radiative effects of aerosols depend not only on their physical and chemical properties, but also on their distribution in the atmosphere. Despite the important role of the vertical distribution of aerosols in the atmosphere, default climatological profiles are commonly used in modeling studies. Uncertainties related with the use of default profiles have been roughly analyzed and discussed in the existing bibliography.

In the context of the present study we simulated the downwelling and upwelling irradiance, heating rates, and the actinic flux at different altitudes, from 0 to 8 km, in the atmosphere. Simulations were performed for four different European sites – where aerosol mixtures constitute from quite different aerosol species – using a default climatological aerosol extinction profile, and the seasonally and annually averaged extinction profiles for each site from the LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies (LIVAS). By comparing the results, the effect of using a more representative profile of the aerosol extinction coefficient for each of the sites, instead of a default climatological profile, was estimated. In addition to the aerosol profiles, climatological values of aerosol optical properties and water vapor from the AErosol RObotic NETwork (AERONET), the  version 2 Max-Planck-Institute Aerosol Climatologyand (MACv2), the Modis Dust AeroSol (MIDAS) climatology, and atmospheric and land-surface variables from the Copernicus Atmospheric Monitoring System (CAMS), were used as inputs to the libRadtran radiative transfer model. Spectra in the range 280 – 3000 nm were simulated for different solar zenith angles, and the integrals of the spectra, as well as the integrals in the ultraviolet and visible spectral regions were analyzed.

Results of the analyses are presented and discussed in order to study the sensitivity of the radiometric quantities simulated by the model to the used aerosol extinction profile, for each of the four sites. Differences between the products of the simulations when the used aerosol optical depth (AOD) comes from different sources (LIVAS, AERONET, MIDAS, CAMS) have been also investigated. 

Acknowledgements

This study was funded by the EuroGEO e-shape (grant agreement No 820852).

How to cite: Fountoulakis, I., Papachristopoulou, K., Proestakis, E., Gkikas, A., Raptis, P. I., Siomos, N., Kontoes, C., and Kazadzis, S.: Effect of aerosol vertical distribution on the transfer of solar radiation through the atmosphere, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6111, https://doi.org/10.5194/egusphere-egu21-6111, 2021.

Atmospheric aerosol hygroscopicity and reactivity play a significant role in determining aerosol fate, and are affected by composition and other physical properties. Organic aerosol emissions contain fatty acids, along with sugars such as fructose. As surfactants, fatty acids organise into a range of nanostructures (3-D molecular arrangements), dependent on water content and mixture composition. In this study, we were able to demonstrate (and quantify) that the chemical reactivity of this proxy is dependent on its 3-D molecular arrangement. Furthermore, we have determined the effect of each observed nanostructure on hygroscopicity by measuring the swelling of these nanostructures as a function of relative humidity. We did this by coating capillaries with a fatty acid/sugar as a mixture for an urban aerosol, and following structural changes with simultaneous Small-Angle X-ray Scattering (SAXS) and Raman microscopy, at a synchrotron X-ray source. SAXS measured the nano-structural parameters required to follow both the reaction kinetics (ozonolysis) and hygroscopic swelling of each nanostructure. Raman microscopy provided complementary kinetic information and supported these findings. We found that the molecular arrangement of surfactant material has an impact on both the chemical kinetics and hygroscopicity. This has implications for the persistence of particulate matter in the urban environment and surfactant material in the atmosphere.

How to cite: Milsom, A., Squires, A., Terrill, N., Ward, A., and Pfrang, C.: The hygroscopicity and reactivity of fatty acid atmospheric aerosol proxies are affected by nanostructure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7326, https://doi.org/10.5194/egusphere-egu21-7326, 2021.

Many large-scale epidemiological studies have shown a close correlation between adverse human health effects and ambient PM_2.5 exposure. A report by the World Health Organisation estimates that 1 out of 8 deaths globally are linked to air pollution. Even though various epidemiological studies underline this argument, the chemical components and physical properties of particulate matter that leads to the observed health effects remains highly uncertain.

            Aerosol oxidative potential defined as the capability of particles to produce reactive oxygen species (ROS) with subsequent depletion of anti-oxidants, naturally present in the human lung, has been widely suggested as measure of their potential toxicity. Due to the fact that ROS (i.e. inorganic and organic peroxides and radicals) are highly reactive, they are therefore short-lived. Subsequently, classical offline analysis, where aerosol particles are typically collected on a filter for 24h, may lead to an underestimation of the oxidative potential.

            Therefore, we developed an online instrument that can continuously measure particle oxidative potential with a high time resolution (10 minutes). We further developed an online instrument described in Wragg et al. (2016) and implemented a physiologically relevant assay to assess aerosol oxidative potential, based on the chemistry of ascorbic acid (Campbell et al. (2019)). Ascorbic acid (AA) is a prevalent naturally occurring anti-oxidant present in the lung and can therefore be used as a proxy to measure the oxidative potential of aerosol. 

            In this work, we further developed the AA online assay based on Campbell et al. (2019), implementing more physiologically relevant chemical conditions such as pH7 and we improved components of the instrument to increase its detection limit. With the current instrument AA oxidation can be quantified via two different spectroscopic methods: one based on fluorescence as described in Campbell et al. (2019) and a newly developed UV-absorption detection system using a liquid waveguide capillary cell (LWCC) which is a very sensitive long pathway (100cm) absorption cell.

            For the fluorescence approach, a limit of detection (LOD) of 0.22 µg/m³ was determined for copper (Campbell et al. (2019)). In comparison, the current detection limit for the UV-absorption based setup is an order of magnitude lower (0.02 µg Cu/m³). This LOD is close to observations of copper concentrations at urban European locations, which are in the range of 0.001-0.009 µg/m³. Using both detection methods, we gain an improved understanding of the oxidation process, because the absorbance method measures AA depletion whereas in the fluorescence method the formation of the AA oxidation product dehydroascorbic is quantified. The online ascorbic acid assay as described will be applied in lab experiments (i.e. flow tubes or smog chamber) as well as for field measurements.

With the improvements of having a more physiological relevant assay and an improved detection method, this instrument is capable of providing a real-time and more realistic estimation of the oxidizing aerosol properties and their potential effect on human health compared to traditional offline methods.

Wragg, F. P. H. et al. (2016), Atmospheric Measurement
         Techniques, 9(10), pp. 4891–4900.

 Campbell, S. J. et al. (2019), Analytical Chemistry, 91, 20, 13088-13095.

How to cite: Utinger, B.: Developing a High Time-Resolution Online Instrument to Quantify Aerosol Oxidative Potential via Ascorbic Acid Oxidation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7482, https://doi.org/10.5194/egusphere-egu21-7482, 2021.

We present the results from a chemical characterization study of ultrafine particles (UFP), collected nearby Frankfurt International Airport where particle size distribution measurements showed high number concentrations for particles with a diameter <50 nm. Aluminium filter samples were collected at an air quality monitoring station in a distance of 4 km to Frankfurt airport, using the 13-stage cascade impactor Nano-MOUDI (MSP Model-115). The chemical characterization of the ultrafine particles in the size range of 0.010-0.018 μm, 0.018-0.032 μm and 0.032-0.056 μm was accomplished by the development of an optimized filter extraction method. An UHPLC method for chromatographic separation of homologous series of hydrophobic and high molecular weight organic compounds, followed by heated electrospray ionization (ESI) and mass analysis using an Orbitrap high-resolution mass spectrometer was developed. Using a non-target screening, ~200 compounds were detected in the positive ionization mode after filtering, in order to ensure high quality of the obtained data. We determined the molecular formula of positively charged adducts ([M+H]⁺; [M+Na]⁺), and for each impaction stage we present molecular fingerprints (Molecular weight vs Retention time, Kroll-diagram, Van-Krevelen-diagram, Kendrick mass defect plot) in order to visualize the complex chemical composition. The negative ionization mode led only to the detection of a few compounds (<20) for which reason the particle characterization focuses on the positive ionization mode. We found that the majority of detected compounds belong to homologous series of two different kinds of organic esters, which are base stocks of aircraft lubrication oils. In reference to five different jet engine lubrication oils of various manufacturers, we identified the corresponding lubricant base stocks and their additives in the ultrafine particles by the use of matching retention time, exact mass and MS/MS fragmentation pattern of single organic molecules. As the relevance of the chemical composition of UFP regarding human health is depending on the mass contribution of each compound we strived for quantification of the jet engine oil compounds. This was achieved by standard addition of purchased original standards to the native sample extracts. Two amines serving as stabilizers, one organophosphate used as an anti-wear agent/metal deactivator and two ester base stocks were quantified. Quantification of the two homologous ester series was carried out using one ester compound and cross-calibration. The quantitative determination is burdened by the uncertainty regarding sampling artefacts in the Nano-MOUDI. Therefore we characterized the cascade impactor in a lab experiment using the ester standard. Particle size distribution measurements conducted parallel to the filter sampling enables the determination of jet engine oil contribution to the UFP mass. Results indicate that aircraft emissions strongly influence the mass balance of 0.010-0.018 μm particles. This contribution decreases for bigger sized particles (0.018-0.056 μm) as presumably more sources get involved. The hereby-introduced method allows the qualitative and quantitative assignment of aircraft emissions towards the chemical composition and total mass of airport related ultrafine particles.

How to cite: Ungeheuer, F., Rose, D., van Pinxteren, D., Ditas, F., Jacobi, S., and Vogel, A. L.: Qualitative and Quantitative Characterization of Airport-related Ultrafine Particles using Liquid Chromatography – High-Resolution Mass Spectrometry (UHPLC/HRMS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7777, https://doi.org/10.5194/egusphere-egu21-7777, 2021.

The chemical composition of aerosols, in both gas and particle phase, is an important factor regarding their properties influencing air quality, weather, climate, and human health. Organic compounds are a major fraction of atmospheric aerosols and their composition depends on chemical processing by atmospheric oxidants and photochemical reactions. These processes are complex due to the abundance of potential reactions and rarely studied over a wider range of atmospheric temperatures. To achieve a better understanding of three different photochemical processes relevant for the atmosphere as well as the capabilities to investigate such processes in our simulation chamber we studied three different organic aerosol systems between 213 K and 293 K in the AIDA simulation chamber at the Karlsruhe Institute of Technology.  With the first system we studied the direct photolysis of 2,3-pentanedion which is a typical carbonyl compound emitted by the food industry but also by trees. In the second system we studied the depletion of pinic and pinonic acid by radicals formed through photolysis of an iron oxalate complex, which acts as the photosensitizer in this system, all present in aqueous aerosol particles. Furthermore, we studied the photolysis of a nitrogen heterocycle in aerosol particles, which can form in the atmosphere by the reaction of dicarbonyls and shows strong absorption in the visible [1].

Photochemical reactions were studied using a new LED light-source simulating solar radiation in the UV and visible. The organic aerosols were generated by nebulizing aqueous solutions containing the aerosol components.  The aerosols were analysed by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a proton transfer mass spectrometer (CHARON-PTRMS) and a high–resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS).  The latter two allow to study the composition of gas phase and particle phase separately.

In this presentation, we will discuss the changes that these organic compounds undergo in gas and particle phase, during photochemical aging at temperatures between 213 and 293 K.

[1] C. J. Kampf, A. Filippi, C. Zuth, T. Hoffmann and T. Opatz, Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects, Phys. Chem. Chem. Phys, 2016, 18, 18353

How to cite: Vallon, M., Gao, L., Song, J., Jiang, F., and Saathoff, H.: Direct and indirect photochemical aging of organic aerosol components as a function of temperature, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8722, https://doi.org/10.5194/egusphere-egu21-8722, 2021.

The coronavirus-19 (COVID-19) pandemic led to government interventions to limit the spread of the disease that are unprecedented in the last decades. Stay at home orders and other measures led to sudden decreases in atmospheric emissions, most visibly from the transportation sector. We present a review of the current knowledge and understanding of the influence of these emission reductions on atmospheric pollutants concentration and notably air quality with a focus on NO₂, PM_2.5, and O₃ based on more than 200 papers utilizing observations from ground-based and satellite remote sensing instruments. We use the government stringency index as an indicator for the severity of lockdown measures and show how key air pollutants change as the stringency index increases. Changes in NO₂ and PM_2.5 mass concentration are well-studied globally. The observed decrease of NO₂ with increasing stringency index is in general agreement with emission inventories that account for the lockdown. Due to the important influence of atmospheric chemistry on O₃ and PM_2.5 concentrations, their responses may not be linear with respect to primary pollutants. At most sites, we found O₃ increased, whereas PM_2.5 decreased slightly, with increasing stringency index. Changes in the PM_2.5 composition are found to be understudied and not well-quantified so far. We highlight future research needs for utilizing the emerging data sets covering a full seasonal cycle as a preview of a future state of the atmosphere in a world with targeted permanent reductions of emissions. Finally, we emphasize the need to account for the effects of meteorology, long-term trends, and atmospheric chemistry when determining the lockdown effects on pollutant concentrations, especially on PM_2.5.

How to cite: Gkatzelis, G., Gilman, J., Brown, S., Eskes, H., Gomes, R., Lange, A., McDonald, B., Peischl, J., Petzold, A., Thompson, C., and Kiendler-Scharr, A.: The Global Impacts of COVID-19 Lockdowns on Short-Lived Climate Forcers: Highlights from a Critical Review, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10636, https://doi.org/10.5194/egusphere-egu21-10636, 2021.

Τhe composition of wintertime urban air in Patras, Greece was investigated during early 2020 focusing on the role of biomass burning. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a Proton Transfer-Reaction Mass Spectrometer (PTR-MS) were deployed. Additionally continuous measurements of the aerosol size distribution from 10 nm to 10 μm were performed, as well as measurements of the size-resolved aerosol composition using a Micro-Orifice Uniform-Deposit Impactor, black carbon (BC) concentrations using an SP2, aerosol absorption, brown carbon concentrations, and reactive oxygen species (ROS). A number of low-cost sensors for particles and vapors was also deployed in the city.

               The PM_2.5 concentration peaked during the early evening reaching up to 150 µg m^-3. PM₁ aerosol (23 µg m^-3 on average) was mainly composed of organics (69%) with the rest being BC (11%), sulphate (10%), nitrate (5%), ammonium (4%) and chloride (1%). Positive Matrix Factorization (PMF) of the measurements of the AMS indicated that biomass burning due to residential heating was the dominant source of PM₁ during the campaign accounting for 53% of the total OA with the rest being the oxygenated organic aerosol (ΟΟΑ) at 25%, the cooking OA (COA) at 12% and the traffic related hydrocarbon-like OA (HOA) at 10%.

               The biomass burning contribution was also evident in several volatile organic compounds (VOCs) detected by the PTR-MS. Biogenic species such as isoprene and the monoterpenes showed clear relation to wood burning, while most of the aromatic compounds were related both to traffic and wood burning. The latter was also true for other gas species measured such as CO, NO_x etc. Biomass burning was also a major contributor to the ROS measured as well as the brown carbon.

How to cite: Kaltsonoudis, C., Florou, K., Kodros, J., Jorga, S., Vasilakopoulou, C., Baliaka, C., Aktypis, A., Nenes, A., and Pandis, S.: Contribution of residential wood burning to wintertime air pollution in an urban area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10670, https://doi.org/10.5194/egusphere-egu21-10670, 2021.

Singlet oxygen (¹O₂) is a reactive oxygen species that has recently gained attention as a competitive oxidant in the atmosphere. This excited state of molecular oxygen is formed by indirect photochemistry in the presence of chromophoric dissolved organic matter (DOM) as sensitizers, molecular oxygen and sunlight. The produced highly reactive intermediate ¹O₂ is then capable of oxidizing and degrading many organic atmospheric components, thereby affecting their lifetime in the atmosphere. Despite this influence on atmospheric fate, the spatiotemporal distribution of ¹O₂ in particular matter (PM) is currently unknown. We hypothesized that brown carbon in biomass burning organic aerosols emitted during winter in Switzerland would lead to higher ¹O₂ steady-state concentrations in PM compared to summer. Therefore, to advance atmospheric ¹O₂ research, we investigated the ¹O₂ sensitizing ability of organic aerosols sampled on 24-hour PM10 filters. Specifically, these filters were collected throughout 2013 in Frauenfeld and San Vittore in Switzerland, characterized as urban background and rural traffic measurement stations, respectively. We extracted the water-soluble organic components and quantified ¹O₂ steady state concentrations as well as ¹O₂ quantum yield. The quantum yield enhances the data intercomparison as this value shows the normalization of ¹O₂ production as a function of the rate of absorbance of the organic aerosols. In our ongoing efforts of expanding the spatiotemporal scale of our measurements, our results from Frauenfeld so far show a range between 0.38 – 6.05 · 10^-13 M for ¹O₂ steady state concentrations and quantum yields up to 2.1± 0.5%. In preliminary experiments, samples from the rural site San Vittore show similar values, with potentially higher values during periods of significant biomass burning contributions. The values underline ¹O₂’spotential importance for atmospheric processing, e.g. comparing to Manfrin et al. (ES&T, 2019)¹ who reported ¹O₂ steady state concentrations of 3 ± 1 · 10^-14 M from secondary organic aerosols extracts. More importantly, the filter extracts analyzed thus far show a strong seasonal trend, with increased ¹O₂ values and higher variability in winter as compared to summer. This result corroborates the hypothesis that there is more chromophoric DOM present in winter, due to a higher fraction of brown carbon emitted e.g. in biomass burning for residential heating. To extend this analysis, we are currently correlating the results for ¹O₂ with molecular markers based on mass spectrometry data available from previous filter analysis provided by Daellenbach et al., (ACP, 2017)². Finding these correlations will enable the prediction of ¹O₂ sensitizing abilities of organic material present in the aerosols both qualitatively and quantitatively. In all, our work will help constrain the seasonal relevance of ¹O₂ photochemistry in the atmosphere.

References

1. Manfrin, A. et al. Reactive Oxygen Species Production from Secondary Organic Aerosols: The Importance of Singlet Oxygen. Environmental Science & Technology 53, 8553–8562 (2019).
2. Daellenbach, K. R. et al. Long-term chemical analysis and organic aerosol source apportionment at nine sites in central Europe: source identification and uncertainty assessment. Atmospheric Chemistry and Physics 17, 13265–13282 (2017).

How to cite: Bogler, S., Borduas-Dedekind, N., el Haddad, I., Bell, D., and Dällenbach, K.: How quality and quantity of brown carbon influence singlet oxygen production in aqueous organic aerosols, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10743, https://doi.org/10.5194/egusphere-egu21-10743, 2021.

Brown carbon (BrC) aerosol has significant climatic impact due to its ability to absorb solar radiation in the near-ultraviolet and visible spectral range. However, chromophores responsible for light absorption in atmospheric aerosol particles are not well understood in urban areas. Therefore, optical properties and chromophore composition of brown carbon were characterized during March 2020 in downtown Karlsruhe, a city of 300000 inhabitants in southwest Germany.

In this study, total non-refractory particle mass was measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-MS; hereafter AMS). Furthermore, Aerosol particles were collected on filters and analyzed in the laboratory. Filter samples were extracted by methanol and the corresponding solutions were analyzed by excitation-emission spectroscopy (AquaLog), resulting in characteristic light absorption and fluorescence spectra. Furthermore, filters were analyzed by a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-TOF-CIMS; hereafter CIMS) employing iodide ions, which results in the molecular composition of oxygenated organic aerosol compounds.

Our results show that the average light absorption and mass absorption efficiency of brown carbon at 365 nm were (2.8±1.9) Mm^-1 and (1.1±0.2) m² g^-1 respectively. Parallel factor (PARAFAC) analysis allowed for identification of four types of fluorescence in methanol-soluble organic compounds. HULIS-like compounds contributed 47%, road dust-like compounds 19%, biomass burning-like compounds 25%, and protein-like compounds 9%. Positive matrix factorization (PMF) analysis of organic detected by AMS led to five characteristic organic compound classes. Of these five classes, the biomass burning organic aerosol showed a correlation coefficient of r2=0.7 with the biomass burning like factor from the fluorescence analysis. Oxygenated organic aerosol components had potentially lower fluorescence intensity and mass absorption coefficiency. Furthermore, five nitroaromatic compounds were identified by CIMS (C7H7O3N, C7H7O4N, C6H5O5N, C6H5O4N, and C6H5O3N) which contributed 0.2%-0.9% to total organic mass, but can explain 3%-6% of the absorption at 365 nm.

How to cite: jiang, F., Saathoff, H., song, J., gao, L., vallon, M., leisner, T., and norra, S.: Chemical characteristics and optical properties of brown carbon aerosol in Karlsruhe during winter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10899, https://doi.org/10.5194/egusphere-egu21-10899, 2021.

China, with rapid urbanization and industrialization, has experienced severe air quality deterioration in recent decades. To release heavy air pollution in China, Chinese government implement the Clean Air Action Plan initiated in 2013. Fine particles (PM_2.5) concentrations have shown significant declines over the nationwide, which attribute to mitigating anthropogenic emission of primary PM_2.5, and precursor gases of nitrogen oxides (NOx), sulfur dioxide (SO₂), and carbon monoxide (CO). However, surface ozone concentrations have unexpectedly increased during the implementation of 2013 to 2019. China has an average trend of 1.9 ppbv a^-1 in same period, measured by ambient monitoring station of China’s Ministry of Environment and Ecology (China MEE). Notably, surface ozone has faster increased trend in megacity clusters, with 3.3 ppbv a^-1 inBeijing-Tianjin-Hebei, 1.6 ppbv a^-1 in Yangtze River Delta, 1.1 ppbv a^-1 in Pearl River Delta. At shorter temporal scale, the lockdown during outbreak of COVID-19, in which human activities dramatically decreased with reduction of industry and transport emission, witnessed exceeding 30% increase of maximum daily 8h average (MDA8) O₃, in major cities (e.g., Shanghai, Hangzhou, Hefei etc.). The investigated results suggested simultaneous controlling concentration of PM2.5 and ozone should coordinate inner physical and chemical processes. In this study, the weather Research and Forecasting with Chemistry was applied to reproduce the following two pathways: (1) The response of surface ozone to modification of photolysis by changed radiation budgets induced by scattering and absorbing aerosols; (2) The further impacts of altered atmospheric oxidizing capacity on surface ozone and aerosols concentrations. This study can provide reasonable advice to air pollution control strategies in Chinese megacity clusters.

How to cite: Zhang, Y.: The response of surface ozone to current mitigation strategies for reducing air pollution in Chinese megacity clusters, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14102, https://doi.org/10.5194/egusphere-egu21-14102, 2021.

To mitigate haze pollution in China, a better understanding of the sources of carbonaceous aerosols is required due to the complexity in multiple emissions and atmospheric processes. Here we combined the analysis of radiocarbon and the stable isotope ¹³C to investigate the sources and formation of carbonaceous aerosols collected in two Chinese megacities (Beijing and Xi’an) during severe haze events of “red alarm” level from December 2016 to January 2017. The haze periods with daily PM_2.5 concentrations as high as ~400 µg m^-3 were compared to subsequent clean periods (i.e., PM_2.5 < median concentrations during the winter 2016/2017), with PM_2.5 concentrationsbelow 100 µg m^-3 in Xi’an and below 20 µg m^-3 in Beijing. In Xi’an, liquid fossil fuel combustion was the dominant source of elemental carbon (EC; 44%–57%), followed by biomass burning (25%–29%) and coal combustion (17%–29%). In Beijing, coal combustion contributed 45%–61% of EC and biomass burning (17%–24%) and liquid fossil fuel combustion (22%–33%) contributed less. Non-fossil sources contributed 51%–56% of organic carbon (OC) in Xi’an and fossil sources contributed 63%–69% of OC in Beijing. Secondary OC (SOC) was largely contributed by non-fossil sources in Xi’an (56 ± 6%) and by fossil sources in Beijing (75 ± 10%), especially during haze periods. The fossil vs. non-fossil contributions to OC and EC did not change drastically during haze events in both Xi’an and Beijing. However, compared to clean periods, the contribution of coal combustion to EC during haze periods increased in Xi’an and decreased in Beijing. During clean periods, primary OC from biomass burning and fossil sources constituted ~70% of OC in Xi’an and ~53% of OC in Beijing. From clean to haze periods, the contribution of SOC to total OC increased in Xi’an, but decreased in Beijing, suggesting that contribution of secondary organic aerosol formation to increased OC during haze periods was more efficient in Xi’an than in Beijing. In Beijing, the high SOC fraction in total OC during clean periods was mainly due to elevated contribution from non-fossil SOC. In Xi’an, a slight day-night difference was observed during the clean period, with enhanced fossil contributions to OC and EC during the day. This day-night difference was negligible during severe haze periods, likely due to enhanced accumulation of pollutants under stagnant weather conditions.

How to cite: Ni, H., Huang, R.-J., and Dusek, U.: Dual-carbon isotopic characterization of carbonaceous aerosol reveals different primary and secondary sources in Beijing and Xi’an during severe haze events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12901, https://doi.org/10.5194/egusphere-egu21-12901, 2021.

Atmospheric brown carbon (BrC) is a highly uncertain, but potentially important contributor to light absorption in the atmosphere. Laboratory and field studies have shown that BrC can be produced from multiple sources, including primary emissions from fossil fuel combustion and biomass burning (BB), as well as secondary formation through a number of reaction pathways. It is currently thought that the dominant source of atmospheric BrC is primary emissions from BB, but relatively few studies demonstrate this in environments with complex source profiles.

A field campaign was conducted during a month-long wintertime period in 2020 on the campus of the University of Peloponnese in the southwest of Patras, Greece which represents an urban site. During this time, ambient filter samples (a total of 35 filters) were collected from which the water-soluble BrC was determined using a semi-automated system similar to Hecobian et al. (2010),  where absorption was measured over a 1 m path length. To measure the BrC, a UV-Vis Spectrophotometer was coupled to a Liquid Waveguide Capillary Cell and the light absorption intensity was recorded at 365 and 700 nm. The latter was used as a reference wavelength. We found that the average BrC absorption in Patras at a wavelength of 365 nm was 8.5 ± 3.9 Mm^-1 suggesting that there was significant BrC in the organic aerosol during this period. Attribution of sources of BrC was done using simultaneous chemical composition data observations (primarily organic carbon, black carbon, and nitrate) combined with Positive Matrix Factorization analysis. This analysis showed that in addition to the important role of biomass burning (a contribution of about 20%) and other combustion emissions (also close to 20%), oxidized organic aerosol (approximately 40%) is also a significant contributor to BrC in the study area.

Reference

Hecobian, A., Zhang, X., Zheng, M., Frank, N., Edgerton, E.S., Weber, R.J., 2010. Water-soluble organic aerosol material and the light-absorption characteristics of aqueous extracts measured over the Southeastern United States. Atmos. Chem. Phys. 10, 5965–5977. https://doi.org/10.5194/acp-10-5965-2010

How to cite: Baliaka, C., Kaltsonoudis, C., Florou, K., Jorga, S., Vasilakopoulou, C., Kodros, J., Aktypis, A., Matrali, A., Paraskevopoulou, D., Masiol, M., Pandis, S., and Nenes, A.: Sources of water-soluble Brown Carbon at a South-Eastern European Site, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11903, https://doi.org/10.5194/egusphere-egu21-11903, 2021.

In the high Arctic, the climate is warming faster than in the lower latitudes due to the Arctic amplification. Sea ice is melting and permafrost is thawing, and the scarce vegetation of the Arctic is changing rapidly. All these varying conditions will have an impact on possible emission sources of aerosol precursor gases, thus affecting the New Particle Formation (NPF) in the Arctic atmosphere, of which we still know very little. It is important to study the NPF events, which parameters affect the aerosol phase and how these newly formed aerosols can grow into cloud condensation nuclei sizes. Only then, it is possible to understand how climate change is affecting the aerosol population, clouds and regional climate of the pristine Arctic. The role of the precursor gases like Sulphuric Acid (SA), Iodic Acid (IA), Methane Sulphonic Acid (MSA) and Highly Oxygenated organic Molecules (HOM) in NPF in boreal and urban environments has been explored to a great extent. However, the role of these precursor gases in NPF events in remote locations - devoid of pollution sources and the vegetation - is still ambiguous. Therefore, it is crucial to conduct long-term measurements to study the composition and concentrations of aerosol precursors molecules, nanoparticles and air ions in remote and climatically fragile place like Ny-Ålesund in the Arctic. This research location is not only a natural pristine laboratory to understand the atmospheric processes but also acts as a climate mirror reflecting the most drastic changes happening in the atmosphere and cryosphere. In this study, we aim to enhance the understanding of the role of aerosol precursor gases in new particle formation in Ny-Ålesund, Svalbard.

            We have studied aerosol particle formation now for almost three years in the Ny-Ålesund research village in Svalbard (78° 55' 24.7368'' N, 11° 54' 35.6220'' E.) with the Neutral cluster and Air Ion Spectrometer (NAIS) measuring ~1-40 nm particles and ions. We have conducted measurements with a Chemical Ionization Atmospheric Pressure interface Time Of Flight (CI-APi-TOF) mass spectrometer to understand the chemical composition of organic precursors vapours and abundance of inorganic aerosol precursor gases such as SA, MSA and IA. Additionally,  we have studied the emission and composition of volatile organic compounds on the site during summer-time.

            In this study, we report the time series concentrations of the most common aerosol precursor gases like SA, MSA, IA and HOM from the period 28.6.-25.7.2019, which are responsible for the initiation and/or growth of particles. The variability in the concentrations of these vapours is compared between NPF event and non-event days. The study explores also the role of meteorological parameters like wind speed, wind direction, temperature and humidity on NPF processes.

How to cite: Lehmusjärvi, T., Thakur, R., Beck, L., Sipilä, M., and Jokinen, T.: Studies of the connection between condensable trace gases and aerosol particles in Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12528, https://doi.org/10.5194/egusphere-egu21-12528, 2021.

The Highly Oxidized Molecule Ion Spectrometer (HOMIS) is a novel instrument for measuring the total concentration of highly oxidized molecules (HOM-s) (Bianchi et al., 2019) at atmospheric pressure. The device combines a chemical ionization charger with a multi-channel differential mobility analyzer. The chemical ionization charger is based on the principles outlined by Eisele and Tanner (1993). The charger is attached to a parallel differential mobility analyzer identical to the ones used in the Neutral cluster and Air Ion Spectrometer (NAIS, Mirme 2011), but with modified sample and sheath air flow rates to improve the mobility resolution of the device. The complete mobility distribution in the range from 3.2 to 0.056 cm²/V/s is measured simultaneously by 25 electrometers. The range captures the charger ions, monomers, dimers, trimers but also extends far towards larger particles to possibly detect larger HOM-s that have not been measured with existing instrumentation. The maximum time resolution of the device is 1 second allowing it to detect rapid changes in the sample. The device has been designed to be easy to use, require little maintenance and work reliably in various environments during long term measurements.

First results of the prototype were acquired from laboratory experiments and ambient measurements. Experiments were conducted at the Laboratory of Environmental Physics, University of Tartu. The sample was drawn from a reaction chamber where alpha-pinene and ozone were introduced. Initial results show a good response when concentrations of alpha-pinene and ozone were changed. 

Ambient measurements were conducted at the SMEAR Estonia measurement station in a hemiboreal forest for 10 days in the spring and two months in the winter of 2020. The HOMIS measurements were performed together with a CI-APi-TOF (Jokinen et al., 2012).

References:

Bianchi, F., Kurtén, T., Riva, M., Mohr, C., Rissanen, M. P., Roldin, P., Berndt, T., Crounse, J. D., Wennberg, P. O., Mentel, T. F., Wildt, J., Junninen, H., Jokinen, T., Kulmala, M., Worsnop, D. R., Thornton, J. A., Donahue, N., Kjaergaard, H. G. and Ehn, M. (2019), “Highly Oxygenated Organic Molecules (HOM) from Gas-Phase Autoxidation Involving Peroxy Radicals: A Key Contributor to Atmospheric Aerosol”, Chemical Reviews, 119, 6, 3472–3509

Eisele, F. L., Tanner D. J. (1993), “Measurement of the gas phase concentration of H2SO4 and methane sulfonic acid and estimates of H2SO4 production and loss in the atmosphere”, JGR: Atmospheres, 98, 9001-9010

Jokinen T., Sipilä M., Junninen H., Ehn M., Lönn G., Hakala J., Petäjä T., Mauldin III R. L., Kulmala M., and Worsnop D. R. (2012), “Atmospheric sulphuric acid and neutral cluster measurements using CI-APi-TOF”, Atmospheric Chemistry and Physics, 12, 4117–4125

Mirme, S. (2011), “Development of nanometer aerosol measurement technology”, Doctoral thesis, University of Tartu

How to cite: Koemets, P., Mirme, S., Kooser, K., and Junninen, H.: Newly developed instrumentation for measuring highly oxidized molecules at atmospheric pressure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12911, https://doi.org/10.5194/egusphere-egu21-12911, 2021.

Relative humidity and rates of its change are relevant parameters in atmospheric sciences. Observations of output data of AE-51 aethalometer operating in ACS1000 humidity chamber reveal strong dependence of attenuation on rapid relative humidity changes. Data collected in winter 2020/21 suggests a probability of similar effect occurring during UAV measurements as thermodynamic parameters could change fast during such runs. Two AE-51 devices were connected in the WET and DRY ACS1000 humidity chamber's channels. During periodic relative humidity oscillations, incident negative peaks of equivalent black carbon mass concentration coincide with high negative derivatives of relative humidity. In most extreme cases values of -1000 ng/m3 equivalent black carbon mass concentration were recorded in parallel with relative humidity derivative of -1.5 %/min. These correlations seem to play an important role in atmospheric measurements as vertical profiles of aerosol parameters such as attenuation are collected using UAV runs during which relative humidity varies significantly. Our goal is to propose a correction method to minimise these anomalies.

How to cite: Florczyk, G., Nurowska, K., Han, A., Chiliński, M., and Markowicz, K.: Should black carbon concentration from aethalometer measurements onboard of UAVs be additionally corrected? - What is the impact of rapid relative humidity changes on our measurements?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13398, https://doi.org/10.5194/egusphere-egu21-13398, 2021.

Aerosol acidity and liquid water content (LWC) affect aerosol concentration and composition as well as the fate of the precursor compounds ammonia (NH₃) and nitric acid (HNO₃) [1,2]. Together with temperature, aerosol acidity and LWC determine the gas-particle partitioning of such precursors. In warm seasons, high aerosol acidity and low LWC promote the partitioning of NH₃ to particulate phase as ammonium, while at the same time drive aerosol nitrate to the gas phase as HNO₃. In cold seasons, the opposite effect can be observed. Given that the dry deposition rate of gaseous NH₃ and HNO₃ is up to 10 times faster than the particle phase, the conditions that favour the partitioning of these species to the gas phase also determine the dry deposition rates of reduced and oxidized nitrogen. This process has consequences for the accumulation of aerosols in the boundary layer, as well as the transport and deposition flux of nitrogen species[2].

In the present work, we explore the seasonal variation of aerosol acidity and liquid water content and their estimated effect on nitrogen dry deposition velocity using data collected over three years in Toronto, Canada, from January 2016 to December 2018. Aerosol acidity, in terms of H⁺ concentration, has large inter- and intra-seasonal variability, ranging between 5 and almost 3 orders of magnitude, respectively. By applying the framework developed in Nenes et al. 2020 [1], aerosol formation during winter is sensitive to HNO₃ levels (pH range

~3 and ~6, LWC range ~0.4 and ~ 35.0 μg m^-3), whereas in summer it tends to be insensitive to both NH₃ and HNO₃ (pH range ~1.4 and ~ 4, LWC range ~0.04 and ~10.0 μg m^-3) This insensitive regime indicates that emissions of other precursors such as SO_x and organic aerosol are major sources of aerosol variability in summer. In terms of nitrogen dry deposition, the seasonal variation experiences two regimes: in winter, the deposition is fast for NH₃ and slow for HNO₃, whereas in summer, both deposition of NH₃ and HNO₃ are fast.

In conclusion, the analysis of ambient aerosol data using aerosol pH and liquid water content suggest that in Toronto, emission controls of NO_x in winter and of SO_x in summer would be most beneficial for air quality.

[1] Nenes A., Pandis S., Weber R.J., Russell A., ACP, 20, 3249–3258, 2020

[2] Nenes A., Pandis S., Kanakidou M., Russell A., Song S., Vasilakos P., Weber R.J., ACPD, 20, 266, 2020

How to cite: Nenes, A., Arangio, A. M., Shahpoury, P., and Dabek-Zlotorzynska, E.: Seasonal aerosol acidity and liquid water content: impact on aerosol concentration and nitrogen deposition fluxes in a urban Canadian environment., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14953, https://doi.org/10.5194/egusphere-egu21-14953, 2021.

The particle hygroscopic growth impacts the optical properties of aerosols and, in turn, affects the aerosol-radiation interaction and calculation 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.

The first effort of the AeroCom Phase III – INSITU experiment was to develop an observational dataset of scattering enhancement values at 26 sites to study the uptake of water by atmospheric aerosols, and evaluate f(RH) globally (Burgos et al., 2019). Model outputs from 10 Earth System Models (CAM, CAM-ATRAS, CAM-Oslo, GEOS-Chem, GEOS-GOCART, MERRAero, TM5, OsloCTM3, IFS-AER, and ECMWF) were then evaluated against this in-situ dataset. Building on these results, we investigate f(RH) in the context of other aerosol optical and chemical properties, making use of the same 10 Earth System Models (ESMs) and in-situ measurements as in Burgos et al. (2020) and Titos et al. (2021).

Given the difficulties of deploying and maintaining instrumentation for long-term, accurate and comprehensive f(RH) observations, it is desirable to find an observational proxy for f(RH). This observation-based proxy would also need to be reproduced in modelling space. Our aim here is to evaluate how ESMs currently represent the relationship between f(RH), scattering Ångström exponent (SAE), and single scattering albedo (SSA). This work helps to identify current challenges in modelling water-uptake by aerosols and their impact on aerosol optical properties within Earth system models.

We start by analyzing the behavior of SSA with RH, finding the expected increase with RH for all site types and models. Then, we analyze the three variables together (f(RH)-SSA-SAE relationship). Results show that hygroscopic particles tend to be bigger and scatter more than non-hygroscopic small particles, though variability within models is noticeable. This relationship can be further studied by relating SAE to model chemistry, by selecting those grid points dominated by a single chemical component (mass mixing ratios > 90%). Finally, we analyze model performance at three specific sites representing different aerosol types: Arctic, marine and rural. At these sites, the model data can be exactly temporally and spatially collocated with the observations, which should help to identify the models which exhibit better agreement with measurements and for which aerosol type.

Burgos, M.A. et al.: A global view on the effect of water uptake on aerosol particle light scattering. Sci Data 6, 157. https://doi.org/10.1038/s41597-019-0158-7, 2019.

Burgos, M.A. et al.: A global model–measurement evaluation of particle light scattering coefficients at elevated relative humidity, Atmos. Chem. Phys., 20, 10231–10258, https://doi.org/10.5194/acp-20-10231-2020, 2020.

Titos, G. et al.: A global study of hygroscopicity-driven light scattering enhancement in the context of other in-situ aerosol optical properties, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2020-1250, in review, 2020.

How to cite: Burgos Simón, M. Á., Andrews, E., Titos, G., Benedetti, A., Bian, H., Buchard, V., Curci, G., Kipling, Z., Kirkevåg, A., Kokkola, H., Laakso, A., Letertre-Danczak, J., Lund, M. T., Matsui, H., Myhre, G., Randles, C., Schulz, M., van Noije, T., Zhang, K., and Zieger, P.: First global assessment of modelled aerosol hygroscopicity in the context of other aerosol optical properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15340, https://doi.org/10.5194/egusphere-egu21-15340, 2021.

Cloud-aerosol interactions are responsible for much of the uncertainty in forcing estimates from pre-industrial times and thus also climate sensitivity and future projections. Maybe the most important factor in this is our lack of knowledge about pre-industrial aerosols, their sources and their ability to act as cloud condensation nuclei (CCN). The number of CCN is highly dependent on secondary aerosol formation and in particular how much of this secondary aerosol mass that goes to new particle formation (NPF) and early particle growth, versus growing already large particles even larger. 
Earth system models which seek to model this, face a challenge because we need to represent processes at a very fine scale (nanometers) to a sufficient accuracy, while simultaneously keeping computational costs low. A common approach is to use log-normal modes to represent the sizedistribution, while more computationally expensive sectional schemes are considered closer to first principles. 

In this study, we investigate the effect of a newly developed scheme for early particle growth on the effective radiative forcing from cloud-aerosol interactions (ERF_aci)  in the Norwegian Earth System Model v2 (NorESMv2). The new scheme, referred to as OsloAeroSec, presented in  Blichner et al. (2020), combines a sectional scheme for the growth of the smallest particles (5 - 39.6 nm), with the original semi-modal aerosol scheme which would simply parameterize the growth up to the smallest mode with Lehtinen et al. (2007). This was shown to to improve the representation of CCN relevant particle concentrations, when compared to measurement data.  

We find that ERF_aci is weakened by approximately 10 % with the new scheme (from -1.29  to -1.16 Wm^-2). The weakening originates from OsloAeroSec (the new scheme) reducing particle formation in regions with high aerosol concentrations while increasing it in very pristine regions. We find, perhaps surprisingly, that an important factor for the overall forcing, is that  NPF inhibits aerosol activation into cloud droplets in high-aerosol-concentration regions, while the opposite is true in pristine regions. 
This is because the NPF particles act as a condensation sink, and if they cannot activate directly themselves, they may reduce the growth of the larger particles which would otherwise activate. 
Furthermore, we find that the increase in particle hygroscopicity with present day emissions of sulphate pre-cursors, decreases the size of the activated particles, and thus makes NPF particles more relevant for cloud droplet activation. 

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 (2007): https://doi.org/10.1016/j.jaerosci.2007.06.009.

Blichner, Sara M., Moa K. Sporre, Risto Makkonen, and Terje K. Berntsen. “Implementing a sectional scheme for early aerosol growth from new particle formation in the Norwegian Earth System Model v2: comparison to observations and climate impacts.” Geoscientific Model Development Discussions (2020): https://doi.org/10.5194/gmd-2020-357

How to cite: Blichner, S. M., Sporre, M. K., and Berntsen, T. K.: Reduced effective radiative forcing from cloud-aerosol interactions with improved modelling of early aerosol growth in an Earth System Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15397, https://doi.org/10.5194/egusphere-egu21-15397, 2021.

Dicarboxylic acids (DCAs) are widely distributed in atmospheric aerosols and cloud droplets and are mainly formed by the oxidation of volatile organic compounds (VOCs). For example, glutaric acid and adipic acid are two kinds of the DCAs that can be oxidized by hydroxyl radical (‧OH) reactions in the aqueous phase of aerosols and droplets. In the present study, the temperature- and pH-dependent rate constants of the aqueous OH radical reactions of the two DCAs were investigated by a laser flash photolysis-long path absorption setup using the competition kinetics method. Based on speciation calculations, the OH radical reaction rate constants of the fully protonated (H₂A), deprotonated (HA^-) and fully deprotonated (A^2-) forms of the two DCAs were determined. The following Arrhenius expressions for the T-dependency of the OH radical reaction of glutaric acid, k(T, H₂A) = (3.9 ± 0.1) × 10¹⁰ × exp[(-1270 ± 200 K)/T], k(T, HA^-) = (2.3 ± 0.1) × 10¹¹ × exp[(-1660 ± 190 K)/T], k(T, A^2-) = (1.4 ± 0.1) × 10¹¹ × exp[(-1400 ± 170 K)/T] and adipic acid, k(T, H₂A) = (7.5 ± 0.2) × 10¹⁰ × exp[(-1210 ± 170 K)/T], k(T, HA^-) = (9.5 ± 0.3) × 10¹⁰ × exp[(-1200 ± 200 K)/T], k(T, A^2-) = (8.7 ± 0.2) × 10¹⁰ × exp[(-1100 ± 170 K)/T] (in unit of L mol^-1 s^-1) were derived.

The energy barriers of the H-atom abstractions were simulated by the Density Functional Theory calculations run with the GAUSSIAN package using the M06-2X method and the basis set m062x/6-311++g(3df,2p). The results showed that the energy barriers were lower at the C_β-atoms and are higher at the C_α-atoms of the two DCAs, clearly suggesting that the H-atom abstractions occurred predominately at the C_β-atoms. In addition, the ionizations can enhance the electrostatic effects of the carboxyl groups, significantly reducing the energy barriers, leading to the order of OH radical reactivity as  <  < . This study intends to better characterize the losing processes of glutaric acid and adipic acid in atmospheres.

How to cite: Wen, L., Schaefer, T., and Herrmann, H.: Reaction kinetics of OH radicals with glutaric acid and adipic acid in the aqueous phase, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15624, https://doi.org/10.5194/egusphere-egu21-15624, 2021.

Together with imminent climate action, building a sustainable future for the humanity requires striving for healthier environments. Atmospheric aerosol particles (also referred to as particulate matter, PM) play a key role in defining the air that the future generations will breathe but also the climates they live in, PM being an important short-lived climate forcer but also a key component of air quality and global environmental health hazard. The contribution of aerosol particles has been a key uncertainty in estimates of the Earth’s radiative forcing since the establishment of the Intergovernmental Panel for Climate Change (IPCC) and still remains as the single largest quoted source of uncertainty in the anthropogenic climate forcing during the industrial period. In the latest assessment by the IPCC, the radiative forcing by aerosol particles has been estimated to be -0.45 W m-2 (between -0.95 and 0.05 W m-2) for aerosol-radiation interactions (RFari) and -0.45 W m-2 (between -1.25 and 0 W m-2) for aerosol-cloud interactions (RFaci). Recent reviews indicate no significant reduction in the uncertainty. The large range of possible aerosol forcing values has serious consequences for climate projections and therefore developing strategies for reaching Paris agreement targets. It is currently not possible to say if a reduction in aerosol emissions due to air pollution mitigation and a phase-out of aerosol emissions will result in a noticeable increase in global mean temperature  or in a negligible climate effect. We will discuss the components and reasons of this uncertainty, focusing on those that are important for aerosol-cloud interactions. We will identify critical bottlenecks in 1) scientific understanding of fundamental aerosol and cloud microphysical processes; 2) method development for improving the understanding of aerosol, cloud, and aerosol-cloud processes as well as their representation in Earth System Models (ESMs); and 3) knowledge transfer within and between the relevant research communities. We will argue for key actions to overcome these bottlenecks, giving examples of good practices for breaking new ground in this long-standing problem that continues to intrigue the atmospheric and climate science communities. Besides enhancing the scientific understanding of the Earth system within the realm of natural science based on multiple lines of evidence, and developing novel (e.g. machine learning –based) methodologies for analyzing existing observational data and model output, we call for additional perspectives from social science and humanities on the communication and knowledge transfer practices within atmospheric and climate research. Making the relevant knowledge transfer pathways and processes transparent is urgently needed to enable systematic determination of the actions required to maximally utilize the existing knowledge, and to ensure effective implementation of new results that may help to narrow down the uncertainty associated with aerosols in climate projections. Improved understanding of the role of aerosols in the climate system will result in enhanced credibility of ESMs and hence also tighter constraints for policies aiming for simultaneous climate neutrality and zero pollution targets.

How to cite: Riipinen, I., Ekman, A., Salter, M., and Pulkkinen, K. and the The FORCeS consortium: Is there hope for reducing the uncertainty associated with aerosols in climate projections?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15717, https://doi.org/10.5194/egusphere-egu21-15717, 2021.

Led by the Belgian Institute for Space Aeronomy, the ESA-backed mission PICASSO (PICo-Satellite for Atmospheric and Space Science Observations) successfully launched its gold-plated satellite on an Arianespace Vega rocket in September 2020. PICASSO is a 3U CubeSat mission in collaboration with VTT Technical Research Center of Finland Ltd, AAC Clyde Space Ltd. (UK), and the CSL (Centre Spatial de Liège), Belgium. The commissioning of the two onboard scientific instruments is currently ongoing; once they are operational, PICASSO will be capable of providing scientific measurements of the Earth’s atmosphere. VISION, proposed by BISA and developed by VTT, will retrieve vertical profiles of ozone and temperature by observing the Earth's atmospheric limb during orbital Sun occultation; and SLP, developed by BISA, will measure in situ plasma density and electron temperature together with the spacecraft potential.

Serving as a groundbreaking proof-of-concept, the PICASSO mission has taught valuable lessons about the advantages of CubeSat technology as well as its many complexities and challenges. These lessons learned, along with preliminary measurements from the two instruments, will be presented and discussed.

How to cite: Baker, N., Anciaux, M., Demoulin, P., Fussen, D., Pieroux, D., and Ranvier, S.: PICASSO: The Golden CubeSat, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15865, https://doi.org/10.5194/egusphere-egu21-15865, 2021.

The plant pathogenic bacteria Pseudomonas syringae are capable of inducing ice nucleation at low supercooling due to the presence of INA proteins on the outer cell membrane. Moreover, P. Syringae was shown to survive long-range transport in cold airmasses and redeposition to the earth’s surface with rain and snow. Thus, the life cycle of P. syringae is tightly coupled to the water cycle in the Earth's ecosystem. Understanding the survival mechanism of P. Syringae exposed to atmospheric cloud conditions is a prerequisite for characterization of bacteria as atmospheric ice nucleating particles, describing its dissemination paths and potential role in the spread of plant-pathogenic disease.

In this contribution we report on the viability study of ice nucleating active bacteria in freezing cloud droplets. To investigate the bacterial viability, water droplets containing several bacterial cells with low and high concentration of INA proteins are levitated in an electrodynamic balance (EDB) and cooled down to a temperature of -25°C. After freezing, the droplets are extracted from the EDB and the survival probability of the bacteria is determined by colony counting. A fluorescence stain and a high-speed video camera were used to visualize individual bacteria in the levitated droplets and to study their behavior during freezing.

The results have shown that the survival of bacteria depends on the freezing dynamics of bacteria-containing droplets (growth rate of ice in supercooled water). The P. syringae bacteria with high concentration of INA proteins are capable of inducing freezing at low supercooling and thus inhibit the growth rate of ice crystals, resulting in higher chance to survive the freezing. If high supercooling is achieved, the ice growth rate immediately after nucleation is very high and the survival probability is dramatically reduced.

How to cite: Kiselev, A., Wieber, C., Zoheir Amer, A. E., and Rabe, K.: Viability study of ice nucleating active bacteria (Pseudomonas Syringae) in freezing cloud droplets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16092, https://doi.org/10.5194/egusphere-egu21-16092, 2021.