Urban aerosol particles are one of the largest human health hazards globally. A significant fraction of urban aerosol is secondary, .i.e., formed via atmospheric chemical reactions of emitted trace gases, with secondary organic aerosol (SOA) driving health impacts in urban air. Decades of air quality regulations have substantially reduced the motor vehicle emissions of organic compounds that act as precursors to SOA and ozone pollution. In this presentation we show that volatile chemical products from household chemicals are becoming one of the largest sources of organic vapors in US and European cities. We highlight the potential of such emission sources to form ozone and SOA using data collected during mobile measurements conducted in 2018 and aircraft measurements conducted in the summer of 2023 on NASA's DC-8 aircraft as part of the AEROMMA mission. Moreover, we will emphasize upcoming measurements in Germany utilizing a Zeppelin as an aerial platform, which will allow us to probe the urban “breath” of European cities and quantify the chemical evolution and SOA production from volatile chemical products downwind of urban centers. These measurements will be complemented by controlled atmospheric simulation chamber experiments to oxidize urban emissions and retrieve their SOA yields as a parametrization to be used by chemical transport models.

How to cite: Gkatzelis, G. and the AEROMMA Team: Household Chemicals Amplifying Urban Pollution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4696, https://doi.org/10.5194/egusphere-egu24-4696, 2024.

Surface-active molecules (surfactants) make significant contributions to aerosol emissions, with sources ranging from cooking to sea spray. These molecules alter the cloud droplet formation potential by changing the surface tension of aqueous droplets and thus increasing their ability to grow. They can also coat solid surfaces such as windows (“window grime”) and dust particles. Such surface films are more important indoors due to the higher surface-to-volume ratio compared to the outdoor environment, increasing the likelihood of surface film–pollutant interactions.

A common cooking and marine emission, oleic acid, is known to self-organize into a range of 3-D nanostructures. These nanostructures are highly viscous and as such can impact the kinetics of aerosol and film aging (i.e., water uptake and oxidation). There is still a discrepancy between the longer atmospheric lifetime of oleic acid compared with laboratory experiment-based predictions.

We have created a body of experimental and modelling work focusing on the novel proposition of surfactant self-organization in the atmosphere. Self-organized proxies were studied as nanometer-to-micrometer films, levitated droplets, and bulk mixtures. This access to a wide range of geometries and scales has resulted in the following main conclusions (Milsom et al., Acc. Chem. Res. 2023, 56, 19, 2555–2568): (i) an atmospherically abundant surfactant can self-organize into a range of viscous nanostructures in the presence of other compounds commonly encountered in atmospheric aerosols; (ii) surfactant self-organization significantly reduces the reactivity of the organic phase, increasing the chemical lifetime of these surfactant molecules and other particle constituents; (iii) while self-assembly was found over a wide range of conditions and compositions, the specific, observed nanostructure is highly sensitive to mixture composition; and (iv) a “crust” of product material forms on the surface of reacting particles and films, limiting the diffusion of reactive gases to the particle or film bulk and subsequent reactivity. These findings suggest that hazardous, reactive materials may be protected in aerosol matrixes underneath a highly viscous shell, thus extending the atmospheric residence times of otherwise short-lived species.  

We will also report on our latest work quantifying how hygroscopicity and reactivity of fatty acid atmospheric aerosol proxies is affected by nanostructure: we found that hygroscopicity is linked to nanostructure and is dependent on the geometry of the nanostructure and reaction with ozone revealed a nanostructure-reactivity trend, with notable differences between th varying nanostructures.

How to cite: Pfrang, C., Milsom, A., Squires, A., and Ward, A.: Molecular Self-Organisation in Surfactant Atmospheric Aerosol Proxies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18810, https://doi.org/10.5194/egusphere-egu24-18810, 2024.

There are now many evidence that OH and H₂O₂ can be spontaneously formed at the air – water interface of aqueous droplets due to the presence of a strong electric field (~10⁹ V m⁻¹). OH^– anion has been suggested that it partially exist as an ion pair (OH^...e^-), which may undergo charge separation in the presence of this electric field. This can lead to OH radical and electron production, while H₂O₂ can be formed via subsequent reactions. The presence of organic molecules on aqueous droplet surfaces and the OH radicals that are spontaneously generated can lead to oxidation products formation altering the composition of the particles.

In this work we studied the OH products formation of pure organic aerosols while they interact with water vapour. We investigated the product formation in the absence of OH radicals precursors, in the dark in the range of RH 0 – 100 %. Organic droplets, in a range of diameter 10 to 300 nm, were generated by nebulizing citric acid solutions. The particles passed through a diffusion dryer and entered inside a flow tube reactor. Particles were collected either on filters or by using a spot sampler. The particle phase analysis was performed via Ultra High-Performance Liquid Chromatography coupled with Electrospray Ionization Orbitrap Mass Spectrometry. Gas phase products were also monitored using a VOCUS mass spectrometer.

All the experiments provide evidence that organic droplets can be oxidized while interacting with water vapours. No products were observed under dry conditions. Oxidation products were formed in the particle phase and their production displayed a systematic increase with the increase of RH denoting the enhancement of OH radical generation. At complete humid conditions, products were also observed in the gas phase due to their desorption. H₂O₂ was also monitored in the gas phase confirming that interfacial OH and electron generation can lead to its formation. Results from this study are expected to significantly improve our insights on the interfacial processes that occur in atmospheric droplets and on the atmospheric multiphase oxidation chemistry.

How to cite: Angelaki, M. and George, C.: Spontaneous formation of OH oxidation products at the interfaces of pure organic droplets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1735, https://doi.org/10.5194/egusphere-egu24-1735, 2024.

How to cite: King, M., McGrory, M., and Ward, A.: Atmospheric organic matter forms core-shell aerosol particles on mineral surfaces , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4654, https://doi.org/10.5194/egusphere-egu24-4654, 2024.

How to cite: Peng, J., Huang, X.-F., Peng, Y., Wei, J., Lin, X.-Y., Tang, M.-X., Cheng, Y., Men, Z., Fang, T., Zhang, J., He, L.-Y., Liu, C., Cao, L.-M., Mao, H., Seinfeld, J. H., and Wang, Y.: Microphysical complexity of black carbon particles restricts their warming potential, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6995, https://doi.org/10.5194/egusphere-egu24-6995, 2024.

Oxides of nitrogen (NO_x = NO + NO₂) and nitrous acid (HONO) play crucial roles in forming tropospheric ozone (O₃), hydroxyl radicals (·OH), and secondary aerosols. The photochemical reactions of nitrate aerosol are of significant atmospheric interest as they produce HONO and NO_x, a process termed renoxification. Light-absorbing organic species, particularly chromophoric Brown Carbon (BrC) predominantly derived from biomass burning, are suggested to be key players in renoxification, though the mechanism remains controversial. Here, we investigate BrC-associated renoxification upon irradiation of films containing BrC extracts from authentic biomass-burning aerosols and BrC model compounds using the coated wall flow tube (CWFT) technique. We mimic real-world aerosol conditions by adjusting the pH, nitrate concentration, and relative humidity of the CWFT films, ensuring atmospheric relevance. We show that the renoxification rate is enhanced in the presence of BrC. This is likely due to the photosensitizing effect of BrC, which enhances the reduction of nitrate, rather than the previously proposed surface-enhanced direct photolysis of adsorbed nitrate. Given the efficient use of the solar spectrum from UV to visible light by this photosensitized mechanism and the widespread coexistence of nitrates and BrC in various environmental systems, we suggest BrC-photosensitized renoxification could be a substantial source of HONO and NO_x. This process may significantly influence the trends and distributions of tropospheric O₃, ·OH and secondary aerosols, marking an important, yet largely unexplored, area in atmospheric chemistry.

How to cite: Bao, F., Bell, D., Tronconi, A., Iezzi, L., Chen, Y., Cheung, K. Y., Dällenbach, K. R., and Ammann, M.: Elucidating the role of brown carbon in HONO and NOx production from renoxification of nitrate-containing aerosol, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10263, https://doi.org/10.5194/egusphere-egu24-10263, 2024.

The formation of sulfuric acid (H₂SO₄, SA), a key aerosol precursor in the atmosphere, hinges on the rate-limiting oxidation of SO₂. During the daytime, hydroxyl radical (OH) is the main SO₂ oxidant, but the measured ambient SA concentration suggests the existence of other unaccounted pathways via other oxidants (Berresheim et al., 2014). The nocturnal presence of SA in marine environments is particularly interesting as the formation mechanism is not straightforward due to the lack of photochemical reactions. In marine environments, molecular iodine and iodocarbons are prevalent, and their reactions with the nitrate radical (NO₃) are known sources of nighttime IO and OIO radicals (Saiz-Lopez and Plane, 2004). OIO has low daytime concentrations due to its large photolysis cross-section but can accumulate during nighttime. In the absence of a photolysis sink, OIO predominantly undergoes self-reaction, leading to the generation of the iodine oxide I₂O₄ at nighttime. The reported lifetime of I₂O₄ against the thermal decomposition back to OIO + OIO is about 30 seconds, which means that it is relatively short-lived, but can survive long enough for reactions with other atmospheric trace gases to become relevant (Kaltsoyannis and Plane, 2008).

In this study, laboratory experiments for the reaction of iodine oxides with SO₂ were carried out using a flow reactor coupled with a nitrate-based chemical ionization mass spectrometer (NO₃^--CIMS). The iodine oxides were generated in situ by the reaction of iodine vapors and ozone in the presence of nitrate radical, mimicking the nighttime oxidation of SO₂ to form SO₃ and consequently SA. The experiments were carried out at room temperature and atmospheric pressure conditions. The experiments were complemented by high-level quantum chemical calculations to get detailed insights into the mechanism and feasibility of the oxidation of SO₂ by iodine oxides to produce SA. Among all the formed iodine oxides, I₂O₄ reacts sufficiently fast with SO₂ with a rate coefficient of 2.0×10^-14 molecule^-1 cm³ s^-1 and can thus lead to appreciable concentrations of SO₃. These results suggest that I₂O₄ can be a key SO₂ oxidant in the marine environment and explain a significant fraction of the produced SA in the nighttime.  

References:

Berresheim, H., Adam, M., Monahan, C., O'dowd, C., Plane, J. M., Bohn, B. and Rohrer, F.  Atmos. Chem. Phys. 14, 12209-12223, 2014.

Saiz–Lopez, A. and Plane, J. M. Geophys. Res. Lett. 31, 2004.

Kaltsoyannis, N. and Plane, J.M. Phys. Chem. Chem. Phys., 10, 1723-1733, 2008.

How to cite: Kumar, A., Iyer, S., Barua, S., Seal, P., and Rissanen, M.: Non-conventional oxidation of SO2 by iodine oxides: A source of nighttime sulfuric acid in the marine boundary layer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8987, https://doi.org/10.5194/egusphere-egu24-8987, 2024.

Sulfate comprises an average of 20% of the ambient PM2.5 mass during the winter months in Fairbanks, as indicated by 24-hour average filter measurements. During ALPACA 2022 field campaign (Jan 15^th-Feb28th of 2022), we deployed two aerosol mass spectrometers (AMS) and one aerosol chemical speciation monitor (ACSM) at three urban sites, combined with Scanning Mobility Particle Sizer (SMPS), to examine the evolution of aerosol composition and size distribution at a sub-hourly time scale. During an intense pollution episode (ambient temperature is between -25 and -35 °C), all three instruments (two AMS and one ACSM) exhibit a sharp increase in sulfate mass within a matter of hours, while organic aerosols, black carbon and SO₂ concentrations remain relatively stable. This notable increase in sulfate mass contributes to approximately half of the observed change in ambient PM2.5. The abrupt rise in sulfate mass is concurrent with a substantial increase in particle number density within the accumulation mode (100-1000 nm), suggesting the secondary formation of sulfate onto pre-existing aerosols. We further investigate possible mechanisms and have ruled out the possible role of cloud chemistry and transition metal ion. The rapid formation of sulfate seems to be linked to the ambient level of nitrogen oxides and, possibly, sunlight. Further investigation is underway to elucidate the intricate connections underlying this rapid sulfate formation.

How to cite: Mao, J., Bali, K., Campbell, J., Robinson, E., DeCarlo, P., Ijaz, A., Temime-Roussel, B., D’Anna, B., Simpson, W., and Weber, R.: Direct observation of wintertime secondary formation of sulfate in ambient aerosols in Fairbanks, Alaska, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15588, https://doi.org/10.5194/egusphere-egu24-15588, 2024.

This study aims to analyze the dynamics of aerosol behavior, particularly focusing on particle number size distribution (PNSD) in contrasting environments — coastal and rural areas of the Netherlands. Our goal is to interpret the environmental factors and mechanisms influencing New Particle Formation (NPF) events in these distinct geographic settings, thereby enhancing our understanding of aerosol dynamics in varied environmental conditions. Our results indicate significant differences in particle number concentrations between the sites, with Cabauw showing notably higher concentrations, largely due to Ultrafine Particles (UFPs). Wind patterns strongly influence UFP levels, particularly winds from the direction of Amsterdam airport and the Rotterdam port area. However, the two sites exhibited good agreement (r²=0.62) in the concentration of accumulation mode particles, suggesting a regional rather than local source. Seasonal variations in nuclei mode particles were observed for both sites, with concentrations peaking in summer and diminishing in winter. 

Our analysis extends to PNSD clusters and NPF classes. The results suggest that NPF events are typically associated with high solar radiation, lower relative humidity, higher temperature, and higher SO₂ and O₃, but lower NOx. The growth of these newly formed particles often relies on stable diffusion radiation conditions, while frequent cloud occurrence impedes particle growth. Additionally, particle size growth is often accompanied by increased concentrations of organics, nitrate, and ammonium. Notably, two distinct NPF episodes in the morning and at noon were observed at Cabauw. Suppressed growth of morning particles often coincides with higher NOx concentrations. In contrast, Lutjewad often experienced noon NPF events, which demonstrated sustained growth in particle size until the following day. These findings underscore the influence of local environmental conditions on aerosol dynamics.

How to cite: Liu, X., Henzing, B., Mulder, J., and Dusek, U.: Two-year observations of aerosol size distributions: investigating new particle formation at coastal and rural sites in the Netherlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16529, https://doi.org/10.5194/egusphere-egu24-16529, 2024.

Atmospheric aerosols exhibit considerable variability in size, spanning a broad range with a difference of four orders of magnitude between the smallest and largest particles. The spatiotemporal heterogeneity in natural and anthropogenic emission sources results in significant variability in aerosol properties, making it extremely hard to precisely quantify aerosol’s climatic effect. New particle formation (NPF, via gas-to-particle conversion) is the largest source of aerosol numbers to the terrestrial atmosphere, and therefore ultrafine particles (particles less than 100 nm diameter). The growth of newly formed particles or primary particles can significantly alter the total aerosol mass and composition which has implications for Earth’s radiation budget and hydrological cycle via aerosol’s direct and indirect effects, respectively. In the Indian context, NPF has been poorly studied in the absence of state-of-the-art instrumentation to characterize atmospheric NPF events. The main objective of this study is to quantitatively assess the role of NPF in the size-segregated particle number concentration in an urban location, Hyderabad. Here, we have used long-term (2019-2022) measurements of particle number size distributions from the nano Condensation Nucleus Counter (nCNC) in the size range of 1 to 3 nm and the Scanning Mobility Particle Sizer (SMPS)  in the size range from 10 nm to 514 nm. Measurements were conducted at the University of Hyderabad campus site. The observation days were broadly categorized into three event types, namely NPF, non-event and undefined based on the visual inspection of the contour plot of particle number size distributions. We additionally utilized in-situ measurements of particulate matter with a diameter smaller than 2.5 µm (PM_2.5) to identify polluted days following the NAAQS criteria (days with PM_2.5 > 60 µg m^-3). The size-segregated particle number concentrations in the cluster mode (sub-3nm), nucleation mode (10-25 nm), Aitken mode (25-100 nm), and accumulation mode (100-514 nm) were calculated for each identified event type. The size-segregated particle number concentrations showed a distinct seasonal pattern, with the highest particle number concentrations during the spring (March - May) and the lowest during the winter months (December - February). The highest particle number concentrations in spring coincide with the highest frequency of NPF event occurrence.  Amongst them, the cluster-mode particles constituted the largest fraction of particle number concentrations and the accumulation-mode particles constituted the lowest. The cluster mode particle number concentrations were found to be the highest during NPF event days than other event types. The positive association between cluster mode particles and PM_2.5 indicates that NPF is not inhibited at high pre-existing particle concentrations unlike in the USA and EUROPE. This suggests that the balance between the precursor vapour concentrations and the pre-existing particle concentrations decides when NPF will trigger in the polluted boundary layer under a given atmospheric condition. However, the negative association between nucleation mode particles and PM_2.5 suggests that not all cluster mode particles grow to nucleation mode size. 

How to cite: Kanawade, V., Sebastian, M., Mittal, N., and Jokinen, T.: Characteristics of size-segregated particle number concentrations in an urban location in India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-861, https://doi.org/10.5194/egusphere-egu24-861, 2024.

New particle formation involving organic compounds has been identified as an important process affecting aerosol particle number concentrations in the global atmosphere. Here a global chemistry-climate model has been developed to include explicit chemical reactions of highly oxygenated molecules (HOMs) and accretion products based on monoterpene-derived peroxy radical (RO₂) unimolecular autoxidation and self- and cross-reactions with other RO₂ species. The improved model incorporates a comprehensive biogenic organic nucleation scheme including heteromolecular nucleation of sulfuric acid and organics, neutral pure organic nucleation, and ion-induced pure organic nucleation. These organic-related mechanisms are combined with an inorganic nucleation scheme derived from published chamber experimental data from the CLOUD project. Additionally, the organic condensational growth rate for newly formed particles (sub-20nm) is taken into account. The updated model captures the occurrence frequency of new particle formation events (normalized mean bias, NMB changes from -96% to -15%) and shows reasonable agreement with measured rates of nucleation (NMB changes from -97% to -64%) and growth (NMB changes from -54% to 39%) globally except in China (NMB of nucleation rate > -100%). The model successfully reproduces surface-level aerosol number concentrations over oceans and vertical profiles over the Amazon Basin. Globally, we find that organics contribute to 45% of the annual average vertically integrated nucleation rate and 25% of the vertical mean growth rate. The inclusion of organic-related processes leads to a 39% increase in the global annual mean aerosol concentration and a 33% increase in cloud condensation nuclei at 0.5% supersaturation compared to a simulation with only inorganic nucleation. Our work also indicates that organic initial growth is more important for particle number than organic nucleation on global average.

How to cite: Shao, X., Wang, M., Carslaw, K., Dong, X., and Liu, Y.: Global Modeling of Organic-related New Particle Formation and its Contribution to Global Aerosol Number Concentrations using CAM6-Chem, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5978, https://doi.org/10.5194/egusphere-egu24-5978, 2024.

In this study, we present the measurement results of stable carbon isotope ratio (δ¹³C) performed on a one-year aerosol samples (n = 96, 24h time resolution during Sep. 2013 - Aug. 2014) for dicarboxylic acids (hereafter “diacids”) and related compounds in PM₁ at a rural background site National Atmospheric Observatory Košetice (NAOK), Czech Republic, Central Europe. In previous study on the molecular distributions of diacids (Vodička et al., 2023a), we observed a distinct seasonal variation in the composition of diacids in PM₁. In winter, approximately 75% of the organic aerosols originated from anthropogenic sources, whereas in summer, over 75% were attributed to biogenic sources. The objective of this study was to investigate whether these differences are reflected in δ¹³C of diacids.

In general, we observed higher δ¹³C values for lower carbon molecules (Vodička et al., 2023b). A comparison of δ¹³C values of major diacids (oxalic (C₂), succinic (C₄), malonic (C₃), azelaic (C₉)) with those from other background sites, especially in Asia, shows similar values to those from the European site. This comparison also demonstrated that C₂ is more enriched with ¹³C at background sites than at urban ones. In general, we did not observe significant seasonal differences in δ¹³C values of diacids at NAOK. We observed statistically significant differences (p value < 0.05) between winter and summer δ¹³C values solely for C₄, glyoxylic (ωC₂), glutaric (C₅) and suberic (C₈) acids.

The only significant correlations between δ¹³C of C₂ and δ¹³C of C₃ were found in spring and summer, suggesting that the oxidation of C₃ to C₂ is significant in these months with a strong contribution from biogenic aerosols. The strongest season-independent annual correlation was observed between C₂ and C₄, the two dominant dicarboxylic acids. Therefore, C₄ appears to be the main intermediate precursor of C₂ throughout the whole year.

Acknowledgement:

This conference contribution was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project ACTRIS-CZ-LM2023030, by the Czech Science Foundation grant No. 20–08304J 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.

References:

Vodička, P., Kawamura, K., Deshmukh, D.K., Pokorná, P., Schwarz, J., Ždímal, V., 2023a. Anthropogenic and biogenic tracers in fine aerosol based on seasonal distributions of dicarboxylic acids, sugars and related compounds at a rural background site in Central Europe. Atmos. Environ. 299, 119619. doi:10.1016/j.atmosenv.2023.119619

Vodička, P., Kawamura, K., Schwarz, J., Ždímal, V., 2023b. A year-round observation of δ¹³C of dicarboxylic acids and related compounds in fine aerosols: Implications from Central European background site. Chemosphere 337. doi:10.1016/j.chemosphere.2023.139393

How to cite: Vodička, P., Kawamura, K., Schwarz, J., and Ždímal, V.: Exploring seasonal variations in δ13C of dicarboxylic acids in fine aerosols: Insights from a Central European background site, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5233, https://doi.org/10.5194/egusphere-egu24-5233, 2024.

Acidity is one central parameter in atmospheric multiphase reactions, influencing aerosol formation and its effects on climate, health, and ecosystems. Weak acids and bases, mainly CO₂, NH₃, and organic acids, are long considered to play a role in regulating atmospheric acidity. However, unlike strong acids and bases, their importance and influencing mechanisms in a given aerosol or cloud droplet system remain to be clarified. Here, we investigate this issue with new insights provided by recent advances in the field, in particular, the multiphase buffer theory. We show that, in general, aerosol acidity is primarily buffered by NH₃, with a negligible contribution from CO₂ and a potential contribution from organic acids under certain conditions. For fogs, clouds, and rains, CO₂, organic acids, and NH₃may all provide certain buffering under higher pH levels (pH > ∼4). Despite the 10⁴to 10⁷ lower abundance of NH₃and organic weak acids, their buffering effect can still be comparable to that of CO₂. This is because the cloud pH is at the very far end of the CO₂multiphase buffering range. This Perspective highlights the need for more comprehensive field observations under different conditions and further studies in the interactions among organic acids, acidity, and cloud chemistry.

How to cite: Zheng, G., Su, H., and Cheng, Y.:  Role of Carbon Dioxide, Ammonia, and Organic Acids in Buffering Atmospheric Acidity: The Distinct Contribution in Clouds and Aerosols , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13623, https://doi.org/10.5194/egusphere-egu24-13623, 2024.

Particulate air pollution in Korea is influenced by both local emissions and the transportation of particles and precursors in continental outflows. Alongside local high-NO_x and NH₃ conditions, the inorganic-rich and hygroscopic transported particles enhance the gas-particle partitioning of inorganic precursor gases (HNO₃, NH₃) into particulate nitrate and ammonium, synergistically resulting in heavy haze pollution. Local source characteristics can impact concentrations of precursor gases and particle acidity, which are crucial factors in inorganic gas-particle partitioning. However, the episodic or background effects of transported particles and precursors make it challenging to clearly identify the local influences of emission source characteristics on chemical composition and concentrations. In this study, we investigated local effects on the gas-particle partitioning into nitrate and ammonium using hourly data of PM_2.5 chemical compositions, NH₃ concentration, and meteorological variables from three different sites in Korea: a typical urban site in Seoul, an industrial site in Ansan, and a rural site affected by industrial sources in Seosan. To isolate the effect of local characteristics from the impact of long-range transport from China, backward trajectories and wind speed were additionally utilized. Partitioning ratios of total HNO₃ (HNO₃ gas + particulate nitrate) and total NH₃ (NH₃ gas + particulate ammonium) were analytically calculated by using particle acidity and liquid water contents from the ISORROPIA II thermodynamic model. Results show that the particle acidity from the three sites is not significantly different, despite a large difference in total HNO₃ and total NH₃ concentrations. However, high relative humidity and liquid water content at the coastal-industrial site, Ansan, can result in a larger nitrate fraction. Local characteristics of secondary inorganic aerosols depend not only on different local source characteristics but also on different local meteorological conditions, particularly relative humidity, which affects nitrate and ammonium partitioning.

How to cite: Seo, J., Kim, J. Y., Kim, K. H., and Kim, J. B.: Local influences of emission source characteristics and meteorological factors on nitrate and ammonium partitioning in Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15070, https://doi.org/10.5194/egusphere-egu24-15070, 2024.

Nitrogen oxide (NO_X) in the atmosphere causes oxidation reactions with photochemical radicals and volatile organic compounds, causing ozone (O₃) accumulation. In the composition of NO_y, NO_X accounts for the highest portion, and followed by nitrous acid (HONO) and nitric acid (HNO₃). HONO significantly contributes to the reaction cycle of NO_X and hydrogen oxide (OH). The generation of OH radicals and nitric oxide by photolysis is the main HONO removal mechanism in the morning. The OH radicals generated at this time trigger O₃ accumulation in the atmosphere, affecting photochemical smog in urban areas. HNO₃ in the atmosphere is produced by the reaction between NO₂ and OH during the day while N₂O₅ and H₂O during night time. Aerosolization by heterogeneous reactions of HNO₃ is the major mechanism of HNO₃ reduction. Aerosolization (heterogeneous) reactions adversely affect humans and plants by increasing the secondary aerosol concentration in the atmosphere and lowering visibility; therefore understanding the conversion mechanism of HNO₃ to aerosols is important. In this study, HONO, HNO₃, and their precursor gases in the atmosphere were observed using parallel-plate diffusion scrubber-ion chromatography. And a 0-D box model simulated the compositional distribution of NO_y in the atmosphere, and the formation reactions and conversion mechanisms of HONO and HNO₃ were analyzed.

Acknowledgments:

This research was supported by Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE)

How to cite: Kim, K., Lee, C., Choi, D., Han, S., Eom, J., Joo, H., and Han, J.: Elucidating the formation and conversion mechanisms of HONO and HNO3 in the atmosphere of Daejeon, Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14449, https://doi.org/10.5194/egusphere-egu24-14449, 2024.

How to cite: Bimenyimana, E., Pikridas, M., Oikonomou, K., Iakovides, M., Vasiliadou, E., Savvides, C., Mihalopoulos, N., and Sciare, J.: The Cyprus Atmospheric Observatory: A unique outpost to monitor the increase of Middle East Air Pollution , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-852, https://doi.org/10.5194/egusphere-egu24-852, 2024.

Black carbon (BC) aerosol can strongly influence planetary boundary layer (PBL) development and thus severe hazeformation, but its distinct role compared with scattering aerosols are not yet fully understood. Here, combiningnumerical simulation and field observation, we found a “tipping point”, where the daily maximum PBL heightdecreases abruptly when exceeding a critical threshold of aerosol optical depth (AOD), due to a BC-induced decouplingof mixing zones. Because the threshold AOD decreases with increasing BC mass fraction, our results suggest that theabrupt transition of PBL development to adverse conditions can be avoided by reducing the AOD below the threshold,but more efficiently by reducing the BC mass fraction to increase the threshold (e.g., up to 4-6 times more effective inextreme haze events in Beijing). To achieve co-benefits for air quality and climate change, our findings clearlydemonstrate that high priority should be given to controlling BC emissions.

How to cite: Su, H., Wang, J., Wei, C., Zheng, G., Wang, J., Su, T., Li, C., Liu, C., Pleim, J. E., Li, Z., Ding, A., Andreae, M. O., Poeschl, U., and Cheng, Y.: Black carbon-induced regime transition of boundary layer development stronglyamplifies severe haze, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3877, https://doi.org/10.5194/egusphere-egu24-3877, 2024.

Recent investigation of aerosols from global aerosol multi-models show that forward model simulations were unable to reproduce the ground-based station-observed aerosol optical depth (AOD) and their spatial distribution over the Indian subcontinent. Estimation of aerosol-induced radiative effects and its impact on climate requires accurate analysis of aerosols optical properties. In the present study high-resolution aerosol transport simulations are carried out with a state-of-the-art Eulerian chemistry-transport model, CHIMERE, forced externally by Weather Research and Forecasting model as a meteorological driver in offline mode. Simulations are carried out over the Indian domain (6° N to 38° N and 68° E to 99.25° E) at a horizontal resolution of 0.25° × 0.25°. The spatial distribution of pre-monsoon mean AOD at 550 nm is compared with satellite observations for the year 2015. The spatial pattern of AOD showing high values in the Indo-Gangetic Plain (IGP, 0.45-0.55) is consistent with the features of observed AOD from satellite retrievals (0.4-0.55) with a slight over-estimation (30%) in the upper-IGP region. The IGP has a higher AOD than most parts of India attributed to high population density and greater emission sources. Large seasonal mean AOD values are also estimated over the Indian state of Telangana (0.5-0.6) which is over-estimated (25%-35%) as compared to satellite retrievals. The simulated AOD is also found to be in good agreement (NMB: 17% for 16 locations) with AOD from ground-based observations (AERONET and individual measurements) at stations over India. Assessment of anthropogenic and dust AOD showed high influence of anthropogenic aerosols over the IGP region while that of dust over north-western region.

Further, the pre-monsoon shortwave radiative perturbation due to total, dust and anthropogenic aerosols over the Indian region is evaluated at surface (SUR), atmosphere (ATM) and top of atmosphere (TOA). The positive value of the radiative effect signifies warming due to aerosols and vice versa for the negative value of the radiative effect. The radiative effect at TOA due to total aerosols is negative over the north-western region and positive for other parts of India. The net radiative effect of total aerosols at the SUR is cooling (-70 to -80 W m^-2) in contrast to warming (+65 to +80 W m^-2) in the atmosphere. The magnitude of radiative perturbations caused by anthropogenic aerosols is higher compared to dust at SUR and ATM. Anthropogenic aerosols have a net warming effect at TOA (+20 to +50 W m⁻²) in contrast to a net cooling effect (-20 to -40 W m^-2) by dust aerosols. The most substantial values of radiative perturbations due to anthropogenic aerosols are observed over the IGP region while the effect of dust aerosols is prominent over the north-western region of India.

How to cite: Dubey, K. and Verma, S.: Radiative effects of pre-monsoon dust and anthropogenic aerosols over India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14502, https://doi.org/10.5194/egusphere-egu24-14502, 2024.

Due to their ability to absorb and scatter solar radiation, major injections of aerosols can have a significant effect on the atmosphere including impacts on the radiation balance of the Earth and changes in temperature. Given the variability and spatial heterogeneity of their concentration, size and chemical composition, it is important to quantify these aerosols, from remote sensing techniques, in order to better identify their sources and understand their environmental impact from regional to global scale. Satellite instruments, such as the Infrared Atmospheric Sounding Interferometer (IASI) and the Atmospheric Infrared Sounder AIRS for the thermal IR region and FORUM for the far infrared, can give us information about chemical composition (Alalam et al. 2022) and microphysical parameters of the aerosols such as the effective radius, concentration and mass (Deguine et al. 2023). Nonetheless, these techniques require accurate information about the optical properties, specifically the complex refractive index (CRI)   .CRI databases available in the literature however, span over limited wavelength ranges and provide mainly reflectance measurements on bulk materials or pressed pellets. In particular, the latter can have several limitations such as the modification of the microphysical properties of the particles (size distribution and morphology). Furthermore, in pellet samples, the particles are present in a compressed matrix causing modifications of the vibrational modes. For bulk measurements, there is strong underestimation of the scattering signal.  Therefore, the optical constants coming from such techniques are not fitted for aerosols and atmospheric applications (McPheat et al. 2002).

We present an improved retrieval methodology combining an experimental setup that allows simultaneously the measurement of high spectral-resolution extinction spectra (up to 0.5 cm^-1) from far infrared (FIR) (50 µm /200 cm^-1) up to UV (0.25 µm /40,000 cm^-1) and the recording of the size distribution of both fine and coarse particles (Hubert et al. 2017). Introducing these experimental measurements in a numerical iterative process, the real and imaginary parts of the CRI are retrieved using an optimal estimation method (OEM) associated to scattering theories and the single subtractive Kramers-Kronig (SSKK) relation (Herbin et al. 2017).

Kaolinite, one of the main clays found in dust, has been used as a first application of this methodology. For the first time, homogenous values of CRI have been retrieved continuously from FIR to UV for suspended particles. This methodology is also being used to retrieved CRI of biomass burning aerosols (BBA). Preliminary result obtained from residual ashes will be present, showing IR extinction spectra as well as chemical analysis.

How to cite: Chehab, M., Herbin, H., Gosselin, S., Bizet, V., and Petitprez, D.: Aerosols complex refractive indices determination from far infrared to UV: application to dust and residual ashes of biomass burning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10689, https://doi.org/10.5194/egusphere-egu24-10689, 2024.