Aerosol Chemical Composition Research Articles

Importance of aerosol composition and aerosol vertical profiles in global spatial variation in the relationship between PM2.5 and aerosol optical depth

Abstract. Ambient fine particulate matter (PM2.5) is the leading global environmental determinant of mortality. However, large gaps exist in ground-based PM2.5 monitoring. Satellite remote sensing of aerosol optical depth (AOD) offers information to help fill these gaps worldwide when augmented with a modeled PM2.5–AOD relationship. This study aims to understand the spatial pattern and driving factors of this relationship by examining η (PM2.5AOD) using both observations and modeling. A global observational estimate of η for the year 2019 is inferred from 6870 ground-based PM2.5 measurement sites and satellite-retrieved AOD. The global chemical transport model GEOS-Chem, in its high-performance configuration (GCHP), is used to interpret the observed spatial pattern of annual mean η. Measurements and the GCHP simulation consistently identify a global population-weighted mean η value of 96–98 µg m−3, with regional values ranging from 59.8 µg m−3 in North America to more than 190 µg m−3 in Africa. The highest η value is found in arid regions, where aerosols are less hygroscopic due to mineral dust, followed by regions strongly influenced by surface aerosol sources. Relatively low η values are found over regions distant from strong aerosol sources. The spatial correlation of observed η values with meteorological fields, aerosol vertical profiles, and aerosol chemical composition reveals that spatial variation in η is strongly influenced by aerosol composition and aerosol vertical profiles. Sensitivity tests with globally uniform parameters quantify the effects of aerosol composition and aerosol vertical profiles on spatial variability in η, exhibiting a population-weighted mean difference in aerosol composition of 12.3 µg m−3, which reflects the determinant effects of composition on aerosol hygroscopicity and aerosol optical properties, and a population-weighted mean difference in the aerosol vertical profile of 8.4 µg m−3, which reflects spatial variation in the column–surface relationship.

Seasonal Changes in the Oxidative Potential of Urban Air Pollutants: The Influence of Emission Sources and Proton- and Ligand-Mediated Dissolution of Transition Metals.

The inhalation of fine particulate matter (PM2.5) is a major contributor to adverse health effects from air pollution worldwide. An important toxicity pathway is thought to follow oxidative stress from the formation of exogenous reactive oxygen species (ROS) in the body, a proxy of which is oxidative potential (OP). As redox-active transition metals and organic species are important drivers of OP in urban environments, we investigate how seasonal changes in emission sources, aerosol chemical composition, acidity, and metal dissolution influence OP dynamics. Using a kinetic model of the lung redox chemistry, we predicted ROS (O2 •-, H2O2, •OH) formation with input parameters comprising the ambient concentrations of PM2.5, water-soluble Fe and Cu, secondary organic matter, nitrogen dioxide, and ozone across two years and two urban sites in Canada. Particulate species were the largest contributors to ROS production. Soluble Fe and Cu had their highest and lowest values in summer and winter, and changes in Fe solubility were closely linked to seasonal variations in chemical aging, the acidity of aerosol, and organic ligand levels. The results indicate three conditions that influence OP across various seasons: (a) low aerosol pH and high organic ligand levels leading to the highest OP in summer, (b) opposite trends leading to the lowest OP in winter, and (c) intermediate conditions corresponding to moderate OP in spring and fall. This study highlights how atmospheric chemical aging modifies the oxidative burden of urban air pollutants, resulting in a seasonal cycle with a potential effect on population health.

Evaluating the Importance of Nitrate‐Containing Aerosols for the Asian Tropopause Aerosol Layer

AbstractThe Asian Summer Monsoon (ASM) convection transports aerosols and their precursors from the boundary layer to the upper troposphere and lower stratosphere (UTLS). This process forms an annually recurring aerosol layer near the tropopause. Recent observations have revealed a distinct property of the aerosol layer over the ASM region, it is nitrate‐rich. We present a newly implemented aerosol formation algorithm that enhances the representation of nitrate aerosol in the Community Aerosol and Radiation Model for Atmospheres (CARMA) coupled with the Community Earth System Model (CESM). The simulated aerosol chemical composition, as well as vertical distributions of aerosol size and mass, are evaluated using in situ and remote sensing observations. The simulated concentrations (ammonium, nitrate, and sulfate) and size distributions are generally within the error bars of data. We find nitrate, organics, and sulfate contribute significantly to the UTLS aerosol concentration between 15°–45°N and 0°–160°E. The two key formation mechanisms of nitrate‐containing aerosols in the ATAL are ammonium neutralization to form ammonium nitrate in regions where convection is active, and condensation of nitric acid in regions of cold temperature. Furthermore, including nitrate formation in the model doubles the surface area density in the tropical tropopause region between 15°–45°N and 0°–160°E, which alters the chlorine partitioning and subsequently impacts the rate of ozone depletion.

Seasonal changes in the physicochemical characteristics of atmospheric aerosol at the research station “Ice Base Baranova Cape” (Severnaya Zemlya archipelago)

Since 2017 we have carried out aerosol sampling at the research station “Ice Base Baranova Cape” (Novaya Zemlya Archipelago) with the purpose of studying the variations in aerosol physicochemical characteristics: the concentrations of ions, microelements, organic and elemental carbon (ОС and ЕС), as well as the isotopic composition of carbon δ13C in the aerosol. The average summed concentrations of ions throughout the period of measurements were 1,99 μg/m3, the concentrations of elements were 51,1 ng/m3; and those of ОС and ЕС were 398 and 25 ng/m3, respectively; the isotopic composition of carbon δ13C was–27.6 ‰. The main contribution (73 %) to the ion composition of atmospheric aerosol is due to “marine” ions Na+ and Cl-, and the contribution to the elemental composition is due to terrogenic Fe and Al (71 %). The large enrichment coefficients (with respect to Na+ in sea water) were manifested for ions SO 2-, K+, and Ca2+. Aerosol enrichment by these ions is the largest in the warm period. In the aerosol elemental composition, we identified large enrichment coefficients (with respect to Al in the Earth’s crust) in elements Se, Sn, Sb, Mo, As, Zn, Cu, Cr, Pb, and Cd, indicating their technogenic origin. The nearest sources of aerosol enrichment by technogenic elements are plants for mining and processing mineral resources in the Taymyr Autonomous Okrug. The statistical generalization of the multiyear data allowed us to calculate for the first time the annual average behavior of the chemical composition of aerosol in the study region. With respect to the seasonal variations, the ions and elements can be divided into three groups: 1) with winter maximum (Na+, Cl-, Mg2+, Br-; Se, Cd, V, Co, As); 2) with summer (PO 3-, NH +, CH SO3-, F-) or autumn (Al, Ti, Li, Sr, Fe, Zn, Ba, Ni) maximum; 3) with poorly defined or indefinite variations in other ions (NO -, K+, SO 2-, Ca2+) and elements (Cu, Pb, Mo, W, Sn, Cr, Sb, Mn). As most of the other characteristics, the annual behaviors of the ОС and ЕС concentrations are characterized by the general maximum in the winter-spring period. In addition, a second maximum is manifested in the ОС content in the summer-autumn period. The average monthly carbon isotopic composition in the aerosol varies in the range from –28.3 ‰ (February) to –27.3 ‰ (May).

The chemical composition of secondary organic aerosols regulates transcriptomic and metabolomic signaling in an epithelial-endothelial in vitro coculture

BackgroundThe formation of secondary organic aerosols (SOA) by atmospheric oxidation reactions substantially contributes to the burden of fine particulate matter (PM2.5), which has been associated with adverse health effects (e.g., cardiovascular diseases). However, the molecular and cellular effects of atmospheric aging on aerosol toxicity have not been fully elucidated, especially in model systems that enable cell-to-cell signaling.MethodsIn this study, we aimed to elucidate the complexity of atmospheric aerosol toxicology by exposing a coculture model system consisting of an alveolar (A549) and an endothelial (EA.hy926) cell line seeded in a 3D orientation at the air‒liquid interface for 4 h to model aerosols. Simulation of atmospheric aging was performed on volatile biogenic (β-pinene) or anthropogenic (naphthalene) precursors of SOA condensing on soot particles. The similar physical properties for both SOA, but distinct differences in chemical composition (e.g., aromatic compounds, oxidation state, unsaturated carbonyls) enabled to determine specifically induced toxic effects of SOA.ResultsIn A549 cells, exposure to naphthalene-derived SOA induced stress-related airway remodeling and an early type I immune response to a greater extent. Transcriptomic analysis of EA.hy926 cells not directly exposed to aerosol and integration with metabolome data indicated generalized systemic effects resulting from the activation of early response genes and the involvement of cardiovascular disease (CVD) -related pathways, such as the intracellular signal transduction pathway (PI3K/AKT) and pathways associated with endothelial dysfunction (iNOS; PDGF). Greater induction following anthropogenic SOA exposure might be causative for the observed secondary genotoxicity.ConclusionOur findings revealed that the specific effects of SOA on directly exposed epithelial cells are highly dependent on the chemical identity, whereas non directly exposed endothelial cells exhibit more generalized systemic effects with the activation of early stress response genes and the involvement of CVD-related pathways. However, a greater correlation was made between the exposure to the anthropogenic SOA compared to the biogenic SOA. In summary, our study highlights the importance of chemical aerosol composition and the use of cell systems with cell-to-cell interplay on toxicological outcomes.Graphical

Assessment of Multiple Planetary Boundary Layer Height Retrieval Methods and Their Impact on PM2.5 and Its Chemical Compositions throughout a Year in Nanjing

In this study, we investigate the planetary boundary layer height (PBLH) using micro-pulse lidar (MPL) and microwave radiometer (MWR) methods, examining its relationship with the mass concentration of particles less than 2.5 µm in aerodynamic diameter (PM2.5) and its chemical compositions. Long-term PBLH retrieval results are presented derived from the MPL and the MWR, including its seasonal and diurnal variations, showing a superior performance regarding the MPL in terms of reliability and consistency with PM2.5. Also examined are the relationships between the two types of PBLHs and PM2.5. Unlike the PBLH derived from the MPL, the PBLH derived from the MWR does not have a negative correlation under severe pollution conditions. Furthermore, this study explores the effects of the PBLH on different aerosol chemical compositions, with the most pronounced impact observed on primary aerosols and relatively minimal influence on secondary aerosols, especially secondary organics during spring. This study underscores disparities in PBLH retrievals by different instruments during long-term observations and unveils distinct relationships between the PBLH and aerosol chemical compositions. Moreover, it highlights the greater influence of the PBLH on primary pollutants, laying the groundwork for future research in this field.

International airport emissions and their impact on local air quality: chemical speciation of ambient aerosols at Madrid–Barajas Airport during the AVIATOR campaign

Abstract. Madrid–Barajas Airport (MAD) is the fourth-busiest airport in Europe. The aerosol chemical composition and the concentrations of other key pollutants were measured at the airport perimeter during October 2021 to assess the impact of airport emissions on local air quality. A high-fidelity ambient instrumentation system was deployed at Madrid–Barajas Airport to measure the following: concentrations of organic aerosols (with their composition), black carbon (eBC), carbon dioxide (CO2), carbon monoxide (CO), nitrogen dioxide (NOx), sulfur dioxide (SO2), particulate matter (PM2.5, PM10), total hydrocarbon (THC), and total particle number. The average concentrations of eBC, NOx, SO2, PM2.5, PM10, CO, and THC at the airport for the entire campaign were 1.07 µg m−3, 22.7 µg m−3, 4.10 µg m−3, 9.35 µg m−3, 16.43 µg m−3, 0.23 mg m−3, and 2.30 mg m−3, respectively. The source apportionment analysis of the non-refractory organic aerosol (OA) using positive matrix factorisation (PMF) allowed us to discriminate between different sources of pollution, namely less oxidised oxygenated organic aerosol (LO-OOA), alkane organic aerosol (AlkOA), and more oxidised oxygenated organic aerosol (MO-OOA). The results showed that LO-OOA and MO-OOA account for more than 80 % of the total organic particle mass measured near the runway. Trace gases correlate better with the AlkOA factor than LO-OOA and MO-OOA, indicating that AlkOA is mainly related to primary combustion emissions. Bivariate polar plots were used for pollutant source identification. Significantly higher concentrations of the obtained factors were observed at low wind speeds (<3 m s−1) from the southwest, where two of the runways and all terminals are located. Higher SO2/NOx and CO/eBC ratios were observed when the winds originated from the northeast, where the two northern runways are located. These elevated ratios are attributed to the aircraft activity being the major pollutant source in the northeast area.

A high-throughput, turbulent-mixing, condensation aerosol concentrator for direct aerosol collection as a liquid suspension

Trace measurement of aerosol chemical composition in workplace atmospheres requires the development of high-throughput aerosol collectors that are compact, hand-portable, and can be operated using personal pumps. We describe the design and characterization of a compact, high flow, Turbulent-mixing Condensation Aerosol-in-Liquid Concentrator (TCALC) that allows direct collection of aerosols as liquid suspensions, for off-line chemical, biological, or microscopy analysis. The TCALC unit, measuring approximately 12 × 16 × 18 cm, operates at an aerosol sample flowrate of up to 10 L min−1, using rapid mixing of a hot flow saturated with water vapor and a cold aerosol sample flow, thereby promoting condensational growth of aerosol particles. We investigated the effect of operating parameters such as vapor temperature, growth tube wall temperature, and aerosol sample flowrate, along with the effect of particle diameter, inlet humidity, aerosol concentration, and operation time on TCALC performance. Nanoparticles with an initial aerodynamic diameter ≥25 nm could grow to droplet diameters >1400 nm with an efficiency ≥80%. Good droplet growth efficiency was achieved for sampled aerosol relative humidity ≥9%. We measured complete aerosol collection for concentrations of ≤3 × 105 cm−3. The results showed good agreement between the particulate mass collected through the liquid collector and direct filter collection. The TCALC eliminates the need for sample preparation and filter digestion during chemical analysis, thereby increasing sample recovery and substantially improving the limit of detection and sensitivity of off-line trace analysis of collected liquid samples.

Validation of aerosol chemical composition and optical properties provided by Copernicus Atmosphere Monitoring Service (CAMS) using ground-based global data

Monitoring particulate matter (PM) air pollution in terms of both concentration and composition, is very important due to its effects on human health and climate. In the PRIMARY project we aim at retrieving the aerosol composition from space using the hyperspectral observations from the Italian Space Agency's PRISMA mission. To this end, we are developing a machine learning algorithm trained with synthetic top-of-atmosphere reflectances and underlying aerosol fields. As part of this process, we plan to use the global forecasts from the Copernicus Atmosphere Monitoring Service (CAMS) as the core to generate this synthetic dataset. However, to proceed in this direction, a preliminary assessment of the reliability of this model-based dataset when compared to observations is necessary, also to bias correct the output if needed. With this aim, we assess the representation of the aerosol chemical composition and the related optical properties at selected globally distributed sites in CAMS, comparing the simulations with near-surface aerosol chemical analyses from the SPARTAN network and column sun-photometer observations from the AERONET network. We found that CAMS forecasts skills changed over time due to updates in the modelling system, with the latter two version cycles (46 and 47) being similar. Generally, they reproduce the aerosol composition within a factor of 2. We found a substantial overestimation of organic matter (OM) by a factor of 3. Applying a correcting factor to OM (constant at the global level) warrants a much more realistic representation of PM2.5 total mass and relative fraction of single species in CAMS. From the so derived CAMS aerosol-speciated profiles, we calculate aerosol optical properties, needed for subsequent use in a radiative transfer model. Comparison against AERONET indeed shows that OM bias correction resulted in improvements in Extinction Ångstrom Exponent (α440nm870nm). Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA) and Asymmetry Parameter (g) simulations resulted slightly degraded, confirming the possibility of using CAMS as the base for a synthetic retrieval training dataset.

Aerosol sources and transport paths co-control the atmospheric bacterial diversity over the coastal East China Sea

Airborne bacteria along with chemical composition of aerosols were investigated during five sampling seasons at an offshore island of the East China Sea. Bacterial diversity was the lowest in spring, the highest in winter, and similar between the autumns of 2019 and 2020, suggesting remarkably seasonal variation but little interannual change. Geodermatophilus (Actinobacteria) was the indicator genus of mineral dust (MD) showed higher proportion in spring than in other seasons. Mastigocladopsis_PCC-10914 (Cyanobacteria) as the indicator of sea salt (SS) demonstrated the highest percentages in both autumns, when the air masses mainly passed over the ocean prior to the sampling site. The higher proportions of soil-derived genera Rubellimicrobium and Craurococcus (both Proteobacteria) and extremophile Chroococcidiopsis_SAG_2023 (Cyanobacteria) were found in summer and winter, respectively. Our study explores the linkage between aerosol source and transport path and bacterial composition, which has implication to understanding of land-sea transmission of bacterial taxa.

Air Composition over the Russian Arctic–4: Atmospheric Aerosols

This work presents the analysis of the spatial distribution of number concentration, size distribution, and chemical composition of aerosol particles measured for the first time over the seas of the Russian Arctic. Various types of vertical distribution of the number concentration were recorded, characteristic of both coastal marine and continental areas. Most of them turned out to be of the continental type. Attention is also drawn to the almost complete absence of coarse particles above 2–3 km over all seas. The chemical composition of the Arctic aerosol at altitudes of both 200 m and 5000 m contains ions that can be referred to as both marine and continental. The identifiable carbon- and salt-free elemental part of the aerosol over the Arctic is 3–4 times larger than that of ions. Over all seas and at both altitudes, the Arctic aerosols mainly contain elements of terrigenous origin – Al, Cu, Fe, and Si. Over almost all seas, except the Barents Sea, Si is dominant in the elemental composition of the aerosol, its contribution over the Chukchi Sea reaching 85%. The analysis of backward trajectories showed that in all cases considered, whether the aerosol was formed over the continent or sea, air trajectories passed both over sea and over land. In this case, the formed particles could be enriched with additional ions and elements along their pathway. This work completes a cycle of the papers, devoted to studying air composition, which was carried out over the seas of the Russian Arctic in September 2020. Our results can be used to model the atmospheric processes occurring in the Arctic under the conditions of changing climate.

New insights into black carbon light absorption enhancement: A comprehensive analysis of two differential behaviors

High uncertainty in optical properties of black carbon (BC) involving heterogeneous chemistry has recently attracted increasing attention in the field of atmospheric climatology. To fill the gap in BC optical knowledge so as to estimate more accurate climate effects and serve the response to global warming, it is beneficial to conduct site-level studies on BC light absorption enhancement (Eabs) characteristics. Real-time surface gas and particulate pollutant observations during the summer and winter over Wuhan were utilized for the analysis of Eabs simulated by minimum R squared (MRS), considering two distinct atmospheric conditions (2015 and 2017). In general, differences in aerosol emissions led to Eabs differential behaviors. The summer average of Eabs (1.92 ± 0.55) in 2015 was higher than the winter average (1.27 ± 0.42), while the average (1.11 ± 0.20) in 2017 summer was lower than that (1.67 ± 0.69) in winter. Eabs and RBC (representing the mass ratio of non-refractory constituents to elemental carbon) constraints suggest that Eabs increased with the increase in RBC under the ambient condition enriched by secondary inorganic aerosol (SIA), with a maximum growth rate of 70.6% in 2015 summer. However, Eabs demonstrated a negative trend against RBC in 2017 winter due to the more complicated mixing state. The result arose from the opposite impact of hygroscopic SIA and absorbing OC/irregular distributed coatings on amplifying the light absorbency of BC. Furthermore, sensitivity analysis revealed a robust positive correlation (R > 0.9) between aerosol chemical compositions (including sulfate, nitrate, ammonium and secondary organic carbon), which could be significantly perturbed by only a small fraction of absorbing materials or restructuring BC through gaps filling. The above findings not only deepen the understanding of BC, but also provide useful information for the scientific decision-making in government to mitigate particulate pollution and obtain more precise BC radiative forcing.

Impact of Anthropogenic Aerosol Transport on Cloud Condensation Nuclei Activity During Summertime in Qilian Mountain, in the Northern Tibetan Plateau

AbstractIn this study, we conducted field campaigns at two mountain‐top observatories on the Qilian Mountains (QLM) in the northeastern Tibetan Plateau of China, which plays a vital role in sustaining water resources for the downstream arid and semi‐arid regions. The two observatories, Waliguan Baseline Observatory (WLG) and Laohugou station (LHG), are situated on the eastern and western edge of the QLM, respectively. The objectives of this study were to examine the properties of atmospheric aerosols, CCN concentrations (NCCN) at varying supersaturation levels (SS = 0.2%–1.0%), and the hygroscopic nature of aerosols in the QLM, especially during the formation of orographic cloud. Notably, the average aerosol concentration and NCCN was approximately 2–3 factors higher at WLG compared to LHG. The chemical compositions of aerosols were primarily dominated by sulfate and organic aerosol (OA) at these two sites. A very high hygroscopicity parameter of aerosol calculated using chemical composition was observed at these two sites (0.37 ± 0.03 at LHG vs. 0.30 ± 0.04 at WLG). Enhanced aerosol loading episodes impacted by anthropogenic emission were observed at these two sites. Exploration on high‐loading cases at each site, we found that the CCN activity was dominated by aerosol size, but the chemical processes of aerosol during the formation of orographic cloud could also be important in CCN activity, especially for low SS conditions. These findings collectively underscore the significant impact of anthropogenic air plumes on CCN concentrations in the QLM and their potential influence on precipitation patterns.

Formation of secondary aerosol by 222 nm Far-UVC irradiation on SO2

222 nm UV indoor disinfection using KrCl* excimer lamps has been gaining popularity due to claims of minimal ocular and skin damage from direct irradiation. However, the secondary aerosol formation under irradiation of KrCl* excimer lamps, which could be an inhalation hazard, is less explored. SO2, a well-known precursor of outdoor sulfate aerosol, is also ubiquitous in indoor environments in urban cities in northern China where coal is used for domestic heating and cooking. In this work, we studied secondary aerosol formation by 222 nm irradiation on SO2, using a Go: PAM flow reactor, a scanning mobility particle sizer (SMPS), and a time-of-flight aerosol chemical composition monitor (ToF-ACSM). The formation of sulfate nanoparticles was found much more effective at 222 nm than at 254 nm and under fluorescent lamp (FL) irradiation at the same UV doses and RH, likely due to different SO2 oxidation mechanisms. We have also found that NH3 and cooking volatile organic compounds (CVOC), as other indoor-relevant gases, promoted the formation of secondary aerosols by 222 nm radiation on SO2. Overall, 222 nm disinfection can generate secondary pollutants in indoor environments. Caution should be taken during its indoor applications, especially in areas with high SO2 concentrations such as coal-fueled households.

Winter monsoon brings substantial terrestrial aerosols to Bay of Bengal and adjacent Indian Ocean: Insights from carbon and nitrogen isotopes

It has been currently recognized that air pollutants (e.g., carbon and nitrogen) from South and Southeast Asia have a significant impact on the coastal waters of the northern Indian Ocean. However, the understanding of dynamics and fates of these pollutants in aerosols to the remote ocean through long-distance transportation still needs to be improved. To address this issue, stable isotopic compositions (δ13C, δ15N) of total carbon (TC) and nitrogen (TN) and other geochemical indexes in aerosols are investigated over the Bay of Bengal (BOB) and the adjacent Indian Ocean during the winter monsoon period. The concentrations of TN, TC and aerosol nutrients exhibited a decreasing trend from the northern BOB (N-BOB) to the southern BOB (S-BOB) and Indian Ocean, reflecting the weakening trend of polluted continental influence from the N-BOB to the ocean. The high concentrations of TC (4.28–18.21 μg m−3) in the aerosols of the N-BOB were mainly influenced by the emissions of coal combustion (68 ± 21%), while the high concentrations of TN (0.69–7.31 μg m−3) in the N-BOB were mainly from biofuel/biomass burning (52 ± 31%). In the S-BOB, the lower concentrations of TC (1.42–2.98 μg m−3) and TN (0.38–2.03 μg m−3) mainly originated from the formation of secondary aerosols and the changes in aerosol chemical composition during long-distance transportation from the continent. The primary marine source was responsible for the low TC and TN concentrations over the Indian Ocean. This study quantifies the nitrogen and carbon source shifts from continental anthropogenic activities in the N-BOB to dominant marine and photochemical transformation sources in the remote ocean, quantitatively deepening the understanding of the impact of terrestrial aerosols on the ocean.

Effects of South Asian outflow on aerosol hygroscopicity and cloud droplet activation over the northern Indian Ocean

As a part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB-2018), shipborne measurements of aerosol properties were carried out to study the influence of South Asian outflow on cloud condensation nuclei (CCN) characteristics over the South East Arabian Sea (SEAS) and equatorial Indian Ocean (EIO) during winter, 2018. The poor association between CCN concentration and mass concentrations of the major aerosol species (organic matter, sulfate, and elemental carbon) is observed over SEAS, where airmass is mostly continental. In comparison, the CCN is well-correlated with aerosol mass concentrations over remote EIO. The dependence of CCN activation (at lower supersaturations) on the ultrafine particle fraction differs between SEAS and EIO depending on the mass concentration of organic aerosols. The coexistence of small and hydrophobic aerosols (organics) decreased the CCN activation ratio during ultrafine particle events. The hygroscopicity estimated using the chemical composition of aerosols is comparable to that estimated from CCN measurements over the Indian Ocean, except for the SEAS, where organic aerosols dominate. The effect of outflow aerosols on cloud droplet number concentration (CDNC) is simulated using a parcel model, which showed a good association (R ∼0.96) with CCN measurements over the EIO; however, the estimated CDNC did not follow the CCN variation over the SEAS region. This study highlights the importance of aerosol chemical composition, especially organics, in CCN activation and cloud droplet formation in the South Asian outflow over the Indian Ocean.

Tropical tropospheric aerosol sources and chemical composition observed at high altitude in the Bolivian Andes

Abstract. The chemical composition of PM10 and non-overlapping PM2.5 was studied at the summit of Mt. Chacaltaya (5380 m a.s.l., lat. −16.346950°, long. −68.128250°) providing a unique long-term record spanning from December 2011 to March 2020. The chemical composition of aerosol at the Chacaltaya Global Atmosphere Watch (GAW) site is representative of the regional background, seasonally affected by biomass burning practices and by nearby anthropogenic emissions from the metropolitan area of La Paz–El Alto. Concentration levels are clearly influenced by seasons with minima occurring during the wet season (December to March) and maxima occurring during the dry and transition seasons (April to November). Ions, total carbon (EC + OC), and saccharide interquartile ranges for concentrations are 558–1785, 384–1120, and 4.3–25.5 ng m−3 for bulk PM10 and 917–2308, 519–1175, and 3.9–24.1 ng m−3 for PM2.5, respectively, with most of the aerosol seemingly present in the PM2.5 fraction. Such concentrations are overall lower compared to other high-altitude stations around the globe but higher than Amazonian remote sites (except for OC). For PM10, there is dominance of insoluble mineral matter (33 %–56 % of the mass), organic matter (7 %–34 %), and secondary inorganic aerosol (15 %–26 %). Chemical composition profiles were identified for different origins: EC, NO3-, NH4+, glucose, and C2O42- for the nearby urban and rural areas; OC, EC, NO3-, K+, acetate, formate, levoglucosan, and some F− and Br− for biomass burning; MeSO3-, Na+, Mg2+, K+, and Ca2+ for aged marine emissions from the Pacific Ocean; arabitol, mannitol, and glucose for biogenic emissions; Na+, Ca2+, Mg2+, and K+ for soil dust; and SO42-, F−, and some Cl− for volcanism. Regional biomass burning practices influence the soluble fraction of the aerosol between June and November. The organic fraction is present all year round and has both anthropogenic (biomass burning and other combustion sources) and natural (primary and secondary biogenic emissions) origins, with the OC/EC mass ratio being practically constant all year round (10.5 ± 5.7, IQR 8.1–13.3). Peruvian volcanism has dominated the SO42- concentration since 2014, though it presents strong temporal variability due to the intermittence of the sources and seasonal changes in the transport patterns. These measurements represent some of the first long-term observations of aerosol chemical composition at a continental high-altitude site in the tropical Southern Hemisphere.

A Novel Approach to Assessing Light Extinction with Decade-Long Observations of Chemical and Optical Properties in Seoul, South Korea

A Novel Approach to Assessing Light Extinction with Decade-Long Observations of Chemical and Optical Properties in Seoul, South Korea

Long-term Studies of Atmospheric Aerosol Chemical Composition at the Cape Baranov Ice Base Station

Long-term Studies of Atmospheric Aerosol Chemical Composition at the Cape Baranov Ice Base Station

Multi-year, high-time resolution aerosol chemical composition and mass measurements from Fairbanks, Alaska

Fairbanks-North Star Borough, Alaska (FNSB) regularly experiences some of the worst wintertime air quality in the United States.