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Oceanic suspended particulate matter (SPM) plays important roles in the coupling of climate and biogeochemical cycles via ocean–atmosphere interactions. However, methods for quantifying the properties of SPM in seawater have not yet been well established. Here we present the application of the recently developed complex amplitude sensor (CAS) for analyzing the complex forward-scattering amplitude of individual SPM (0.2–5.0 µm in diameter) obtained at depths of 0–100 m during a research cruise in the western North Pacific. The measured distribution of the complex amplitude indicated that the CAS-derived SPM data could be roughly classified into five major types. Comparison with reference sample's complex amplitude data and scanning electron microscopy analysis suggested that these types could be attributed mainly to diatom fragments, carbonaceous materials (likely organic matter), mineral dusts, iron oxides, or black carbon. Depth profiles revealed that relatively high concentrations of SPM, presumably dominated by diatom fragments and carbonaceous materials with peak diameters of 0.7–1.0 µm, were typically associated with elevated turbidities and chlorophyll a concentrations. Based on this case study, we discuss the practical advantages and limitations of using the CAS to measure size-resolved concentrations of SPM in seawater and to characterize its composition. [ABSTRACT FROM AUTHOR]

The availability of dissolved iron (Fe) limits primary production over some regions of the surface ocean, especially in regions such as the subarctic North Pacific. In this work, we use Fe stable isotope ratios (δ56Fe) in bulk and size-fractionated marine aerosol particles and dissolved Fe of surface seawater in the subarctic North Pacific on Japanese GEOTRACES cruise GP02 (Summer 2017) as a tracer to clarify the relative contribution of combustion and natural Fe in both marine aerosol particles and surface seawater. The bulk aerosols collected in the coastal regions of both East Asia and western North Pacific have total δ56Fe values that are as low as −0.5 ‰ when compared to crustal (+0.1 ‰), with both the water-soluble phase and the fine particles even more fractionated (as low as −1.9 and −2.8 ‰, respectively). The negative correlation between the aerosol δ56Fe signatures and the enrichment factors of Fe and other elements dominated by anthropogenic sources (e.g., lead and cadmium) in these coastal regions indicates the presence of Fe emitted from high-temperature combustion sources, such as coal combustion and metal smelting. In these regions, combustion Fe accounts for 4–13 and 13–45 % of the total and water-soluble aerosol Fe, respectively. The results demonstrate that soluble aerosol Fe sourced from combustion Fe can be equivalent to that sourced from natural dust Fe in these coastal regions. By contrast, the aerosol particles in pelagic regions were near crustal δ56Fe in all particle size fractions, indicating the dominance of natural Fe and little to no combustion Fe. The relationships among the fractional Fe solubility, major ion concentration, Fe species, and δ56Fe indicate that the presence of combustion Fe is the dominant reason for the solubility increase in the coastal regions and that the atmospheric processing of mineral dust during transport is more important in the pelagic regions. The dissolved Fe of the surface seawater at 10 m depth had a consistently higher δ56Fe by up to +1.5 ‰ than that of the simultaneously collected water-soluble aerosol Fe. The pattern of the elevated δ56Fe in the surface seawater corresponds to decreasing Fe concentrations and can be approximated by Rayleigh fractionation; we attribute these elevated surface δ56Fe values to the effect of biological uptake. New Fe fluxes from both the atmosphere and deeper depths are limited at least in summer compared with the biological uptake in the open ocean of the subarctic North Pacific. [ABSTRACT FROM AUTHOR]

Ice nucleating particles (INPs) are rare particles that initiate primary ice formation, a critical step required for subsequent important cloud microphysical processes that ultimately govern cloud phase and cloud radiative properties. Laboratory studies have found that organic‐rich dusts, such as those found in soils, are more efficient INPs compared to mineral dust. However, the atmospheric relevance of these organic‐rich dusts are not well understood, particularly in regions with significant agricultural activity. The Agricultural Ice nuclei at the Southern Great Plains field campaign (AGINSGP) was conducted in rural Oklahoma to investigate how soil dusts contribute to INP populations in the Great Plains. We present chemical characterization of ambient and ice crystal residual particles from a single day of sampling, using single particle mass spectrometry (SPMS) and scanning microscopy. Ambient particles were primarily carbonaceous or secondary aerosol, while the fraction of dust particles was higher in the residual particles. We also observed an unusual particle type consisting of a carbonaceous core mixed with dust fragments on the surface, which was found in higher proportion in residuals. Dust particles measured during residual sampling contained greater proportions of phosphate (63PO2− ${\text{PO}}_{2}^{-}$ and 79PO3− ${\text{PO}}_{3}^{-}$) and lead (206Pb+). Strong sulfate signals were not seen in the residual dust particles measured by the SPMS, while nitrate was slightly depleted relative to ambient dust. This study shows that organic‐rich soils may be important contributors to the ambient INP population in agricultural regions. Plain Language Summary: Ice nucleating particles (INPs) affect climate by causing clouds to freeze at warmer temperatures. However, they are very rare which this means that they are challenging to characterize. Agricultural soils have exhibited high ice nucleation activity in lab studies though their relevance to ambient INP populations is unknown. In this work, we directly measure INP composition in a field campaign at a site in the middle of farmlands to determine whether they are an important source of INPs. We show that dust particles, along with carbonaceous particles mixed with dust, are enriched in INP samples relative to ambient particles. We also show that phosphate (presumed to come from biological fragments) and lead may enhance the IN activity of dust particles. Key Points: Ice nucleating particle composition was directly measured with the ice crystal residual method using two characterization techniquesDust residual particles contained greater phosphate and lead relative to ambient dust particlesCarbonaceous particles internally mixed with dust fragments were found in residual particles measured by SEM/EDX [ABSTRACT FROM AUTHOR]

This study analyses the trends of total aerosol and the main aerosol species over nine capitals in the Baltic Sea basin from 1989 to 2019 based on the Modern-Era Retrospective Analysis for Research and Applications, Version 2 Reanalysis. Aerosol speciation includes mineral dust, sea salt, sulphate (SO4), organic carbon (OC), and black carbon (BC). The mean total aerosol optical depth (AOD) values were the highest (up to 0.216) over the continental capitals (i.e., Warsaw, Berlin, and Vilnius). For each capital, the mean SO4 AOD was the main aerosol species, with a trend specular to total AOD. Apart from Warsaw, the mean BC AOD was the aerosol species with the lowest level. The composition of aerosols changed with respect to the species of anthropogenic origins (i.e., SO4, OC, and BC), with the percentage contribution to the total AOD decreasing for the SO4 AOD and increasing for the BC AOD. Also, the OC AOD showed an increase in the percentage contribution to total AOD for Copenhagen, Oslo, Stockholm, and the continental capitals. Anthropogenic aerosols contributed up to 90.3% of the total AOD, with the highest values over the continental capitals. For each capital, the minimum in the percentage contribution of anthropogenic AOD was between 2007 and 2008, likely due to the global financial crisis. Anthropogenic AOD as a percentage of the total AOD decreased from 1989 to 2008. Both the total and the SO4 AODs decreased over each capital. By contrast, the BC AOD increased over Stockholm, and both the OC and BC AODs increased over Berlin, Copenhagen, and Oslo. The decoupling of carbonaceous aerosols and the SO4 AOD trends was likely due to concurrent factors such as biomass burning and low-sulphur fuel policies. From 2000 to 2019, the inverse relationships between gross domestic products and SO4 AODs suggest a relative decoupling of economic growth from fossil fuels for Oslo, Stockholm, Tallinn, and Vilnius. [ABSTRACT FROM AUTHOR]

Despite the long-term implementation of air pollution control policies in northeast China, severe haze pollution continues to occur frequently. With the adoption of a megacity (Changchun) in northeast China, we analysed the vertical characteristics of aerosols and the causes of aerosol pollution throughout the year using multisource data for providing recommendations for controlling pollution events (i.e., straw burning and fireworks). Based on a ground-based LiDAR, it was found that the extinction coefficient (EC) of aerosols at a height of 300 m in Changchun was highest in winter (0.44 km−1), followed by summer (0.28 km−1), with significant differences from those in warmer regions, such as the Yangtze River Delta. Therefore, it is recommended that air pollution control policies be differentiated between winter and summer. On Chinese New Year's Eve in Changchun, the ignition of firecrackers during the day and night caused increases in the EC at a height of 500 m to 0.37 and 0.88 km−1, respectively. It is suggested that the regulation of firecracker ignition should be reduced during the day and strengthened at night. Based on the CALIPSO and backward trajectory analysis results, two events of dust–biomass-burning composite pollution were observed in March and April. In March, the primary aerosol component was dust from western Changchun, whereas in April, the main aerosol component was biomass-burning aerosols originating from northern and eastern Changchun. Hence, reducing the intensity of spring biomass burning can mitigate the occurrence of dust–biomass-burning composite pollution. These findings can provide emission policy suggestions for areas facing similar issues regarding biomass-burning transmission pollution and firework emissions. [ABSTRACT FROM AUTHOR]

The impact of the anthropic activities in Antarctica is a concerning issue. According to the Scientific Committee on Antarctic Research, attention has to be paid to the next-generation contaminants deriving from both long-range atmospheric transport and local sources. In this study, the capabilities of transmission electron microscopy with energy-dispersive X-ray spectroscopy and Raman micro-spectroscopy were exploited to evaluate the size, morphology, and chemical composition of small micro- and nanoparticles, as well as their aggregates, in surface snow samples collected during the 2020–2021 austral summer in the coastal area of Victoria Land near the Mario Zucchelli research station. The presence of biological particles, mineral dust, sea salts, and small carbonaceous and plastic micro- and nanoparticles was assessed. Sulfate, carbonate, and nitrate minerals were detected in all the samples, whereas polyethylene, poly(ethylene-co-vinyl-acetate), and different kinds of carbonaceous materials were predominantly identified in the samples closest to the research base. The presence of small micro- and nanoparticles containing heavy metals and plastic polymers in samples collected in the areas surrounding the Italian research base highlights the impact of anthropogenic activities on the polar environment, suggesting the need for continuous monitoring to evaluate possible threats to the delicate Antarctic ecosystem. [ABSTRACT FROM AUTHOR]

Large reductions in anthropogenic emissions of particulate matter and its precursor emissions have occurred since the enactment of the Clean Air Act Amendments of 1990. The Interagency Monitoring of Protected Visual Environments network has measured PM2.5 gravimetric mass (mass of particles with aerodynamic diameters less than 2.5 μm, also referred to here as fine mass, "FM") and speciated PM2.5 aerosol composition at remote sites since 1988. Measured species include inorganic anions such as sulfate, nitrate, and chloride, carbonaceous aerosols such as organic (OC) and elemental carbon (EC), and elemental concentrations used to estimate fine dust (FD). Trends in seasonal and annual mean mass concentrations were calculated from 2000 through 2021, a period that includes the largest reductions in emissions. On average, annual mean FM at remote sites in the continental United States has decreased at a rate of −1.8% yr−1. This reduction is largely due to annual mean trends in sulfate (−6.1% yr−1), nitrate (−2.7% yr−1), EC (−2.2% yr−1), FD (−1.3% yr−1), and OC (−0.9% yr−1), although the OC annual mean trend was insignificant. Seasonal and regional mean FM trends varied significantly, with strong reductions in the East in all seasons due to sulfate reductions, and flat and insignificant trends in summer and fall in the West due to the influence of biomass burning emissions on OC trends. Evaluating regional and seasonal mean trends in aerosol composition helps identify sources that continue to adversely impact air quality and hinder progress in FM reductions due to successful regulatory activity. Plain Language Summary: Particulate matter in the atmosphere is made up of many species that have both anthropogenic and natural sources. Thanks to the Clean Air Act Amendments of 1990, anthropogenic emissions that lead to some particulate matter (PM) have decreased, which has resulted in measurable improvements in air quality in remote regions of the United States. Evaluating trends in aerosol measurements from a large‐scale monitoring network over the past two decades has shown that at remote sites in the United States, some aerosol species, like sulfates, nitrates, and some carbonaceous aerosols, have decreased significantly due to the emission reductions; but others, like mineral dust and carbonaceous aerosols from wildfire smoke, have not. In order to continue to make progress in improving air quality in the United States, targeting future sources for emission reductions will require accurate assessments of the contributions from these sources. Dust and wildfire smoke contributions to PM in remote locations across the United States are now larger fractions compared to two decades ago and will likely continue to grow with climate change. Key Points: Fine mass seasonal mean concentrations have significantly decreased in remote regions of the U.S. in response to regulatory activitySulfate aerosols have decreased at the highest rate, followed by nitrate, elemental carbon, fine dust, and organic carbonFlat and insignificant trends in organic carbon and fine mass at western sites in summer/fall were influenced by biomass smoke emissions [ABSTRACT FROM AUTHOR]

Aerosols are key players in the Earth's climate system with mineral dust being one major component of the atmospheric aerosol load. While former campaigns focused on investigating the properties and effects of rather pure mineral dust layers, the A-LIFE (A bsorbing aerosol layers in a changing climate: aging, life time and dynamics) campaign in April 2017 aimed to characterize dust in complex aerosol mixtures. In this study we present ground-based lidar measurements that were performed at Limassol, Cyprus, in April 2017. During our measurement period, the measurement site was affected by complex mixtures of dust from different sources and pollution aerosols from local sources as well as long-range transported. We found mean values of the particle linear depolarization ratio and extinction-to-backscatter ratio (lidar ratio) of 0.27 ± 0.02 and 41 sr ± 5 sr at 355 nm and of 0.30 ± 0.02 and 39 sr ± 5 sr at 532 nm for Arabian dust, and of 0.27 ± 0.02 and 55 sr ± 8 sr at 355 nm and of 0.28 ± 0.02 and 53 sr ± 7 sr at 532 nm for Saharan dust. The values found for pollution aerosols of the particle linear depolarization ratio and the lidar ratio are 0.05 ± 0.02 at 355 nm and 0.04 ± 0.02 at 532 nm, and 65 sr ± 12 sr at 355 nm and 60 sr ± 16 sr at 532 nm, respectively. We use our measurements for aerosol typing and compare that to aerosol typing from sun photometer data, in-situ measurements and trajectory analysis. The different methods agree well for the derived aerosol type, but looking at the derived dust mass concentration from different methods, the trajectory analysis frequently underestimate high dust concentration that were found in major mineral dust events. [ABSTRACT FROM AUTHOR]

The vertical distribution of biomass burning aerosol (BBA) is important in regulating their impacts on weather and climate. The plume‐rise process affects the injection height of BBA and interacts with the air parcel lifting and cloud processes. However, these processes are not represented in most global climate models. In this study, we replaced the fixed vertical profiles of monthly BBA emissions in the Department of Energy's Energy Exascale Earth System Model version 1 (E3SMv1) with an interactive fire plume‐rise model. The vertical distribution of BBA emissions was calculated as a function of ambient thermodynamic conditions from the host E3SMv1, with distributions of fire sizes and sensible heat fluxes derived from the observations. The maximum fire radiative power (FRP) technique was used to determine the fire size. Scaling‐FRP technique is used to calculate the wildfire heat release. Daily BBA emission, superimposed with a fire diurnal cycle retrieved from the satellite observation, was included in model simulations. The model shows improved agreement with satellite retrievals and in situ measurement during the National Oceanic and Atmospheric Administration Wildfire Experiment for Cloud chemistry, Aerosol absorption, and Nitrogen campaign. The model‐observation comparison demonstrates the importance of the plume‐rise model and fire diurnal cycle assumption in determining the BBA fields. We also find that E3SMv1 with new features produces a larger carbonaceous aerosol burden, leading to 0.13 W m−2 warming at the top of atmosphere compared to the default E3SMv1. This highlights the importance of accurately representing the BBA injection height and indicates a no‐linear nature in the BBA‐induced radiative effect. Plain Language Summary: In this study, we replaced fixed vertical profiles of biomass burning aerosols (BBA) used in the default doe's Energy Exascale Earth System Model version 1 (E3SMv1) with an interactive fire plume‐rise model and fire diurnal cycle assumption. The BBA vertical profiles predicted by the model with the new features are in better agreement with the satellite observations and in situ aircraft observations compared to the default version. In addition, the inclusion of the plume‐rise model and fire diurnal assumption also lead to a warming effect as strong as 0.13 W m−2. Key Points: We incorporate an interactive fire plume‐rise model and fire diurnal cycle in the Energy Exascale Earth System Model version 1 (E3SMv1)The new features in E3SMv1 generate biomass burning aerosol vertical profiles that agree better with the observations than the default onesThe E3SMv1 with plume‐rise model and fire diurnal cycle causes a 0.13 W m−2 warming effect compared to the default one [ABSTRACT FROM AUTHOR]

The oxidation of sulfur dioxide (SO2) to sulfate in the atmosphere is an important concern in regional air quality, global climate change, and human health. While gas-phase and liquid-phase oxidation of SO2 are widely regarded as important sources of sulfate, the contribution of the heterogeneous oxidation process on particle surfaces is controversial. Recently, this heterogeneous chemistry has been considered to be an important mechanism that is missing in current models to explain sulfate concentrations observed in haze episodes in East Asia. Therefore, the heterogeneous oxidation of SO2 on particles under the conditions of complex air pollution needs to be reassessed. This review summarizes the fundamental understanding of the heterogeneous reactions of SO2 on solid particles such as mineral dust, black carbon, sea salts, organic aerosol, and so on. The factors affecting the mechanism and kinetics of the heterogeneous reactions of SO2, including coexisting components (O3, NO2, H2O2, NH3, and VOCs), reactive sites, surface properties, relative humidity, and illumination, are reviewed. Reactive oxygen species involved in the heterogeneous oxidation of SO2 on particles are discussed. To our knowledge, while previous reviews have appeared on the oxidation of SO2 in the aqueous-phase, this is the first review on the atmospheric heterogeneous reactions of SO2 on the surface of solid particles, which can be of help in understanding the sulfur cycle in the atmosphere and its environmental impacts. A number of recommendations for future research are also presented. [ABSTRACT FROM AUTHOR]

A high-resolution soot particle aerosol mass spectrometer (SP-AMS) was used to selectively measure refractory black carbon (rBC) and its associated coating material using both the ensemble size-resolved mass spectral mode and the event trigger single particle (ETSP) mode in Houston, Texas in summer 2022. This study was conducted as part of the Department of Energy Atmospheric Radiation Measurement (ARM) program's Tracking Aerosol Convection Interactions Experiment (TRACER) field campaign. The study revealed an average (± 1s) rBC concentration of 103 ± 176 ng m-3. Additionally, the coatings on the BC particles were primarily composed of organics (59 %; 219 ± 260 ng m-3) and sulfate (26 %; 94 ± 55 ng m-3). Positive matrix factorization (PMF) analysis of the ensemble mass spectra of BC-containing particles resolved four distinct types of soot aerosol, including an oxidized organic aerosol (OOABC,PMF) factor associated with processed primary organic aerosol, an inorganic sulfate factor (SO4,BC,PMF), an oxidized rBC factor (O-BCPMF), and a mixed mineral dust/biomass burning aerosol factor with significant contribution from potassium(K-BBBC,PMF). Additionally, K-Means clustering analysis of the single particle mass spectra identified eight different clusters, including soot particles enriched in hydrocarbon like organic aerosol (HOABC,ETSP), sulfate (SO4,BC,ETSP), two types of rBC, OOA (OOABC,ETSP), chloride (ClBC,ETSP) and nitrate (NO3,BC,ETSP). The single particle measurements demonstrate substantial variation in BC coating thickness with coating-to-rBC mass ratios ranging from 0.1 to 100. The mixing state index (χ), which denotes the degree of homogeneity of the soot aerosol, varied from 4 to 94 % with a median of 40 %, indicating that the aerosol population lies in between internal and external mixing but has large temporal and source type variability. In addition, a significant fraction of BC-containing particles, a majority enriched with oxidized organics and sulfate, exhibit sufficiently high κ values and diameters conducive to activation as cloud nuclei under atmospherically relevant supersaturation conditions. This finding bears significance in comprehending the activation of rBC-containing particles as cloud droplets and the origins of CCN in urban areas. Our analysis highlights the complex nature of soot aerosol and underscore the need to comprehend its variability across different environments for accurate assessment of climate change. [ABSTRACT FROM AUTHOR]

Aerosols play an important role in Earth's climate system, and thus long-time ground- based measurements of aerosol optical properties are useful in understanding this role. Ten years of quality-assured measurements between 2010 and 2020 are used to investigate the aerosol climatology in the Cluj-Napoca area, in North-Western Romania. In this study, we analyze the aerosol optical depth (AOD), single scattering albedo (SSA) and angstrom exponent obtained by the CIMEL sun photometer, part of the aerosol robotic network (AERONET), to extract the seasonality of aerosols in the region and investigate the aerosol climatology of the area. Higher aerosol loads are found during July and August. The angstrom exponent has the lowest values in April and May, and the highest in August. The classification of aerosols using AERONET data is performed to separate dust, biomass burning, polluted urban, marine and continental-dominant aerosol mixtures. In addition, the study presents the validation efforts of the Multi-Angle Implementation of Atmospheric Correction (MAIAC) dataset against AERONET AOD over a 10-year period. [ABSTRACT FROM AUTHOR]

Amines/aminiums are recognized for their importance in new particle formation, organic nitrogen cycle, and aerosol forcings. Among the complex sources, the ocean origins and generation pathways of aminiums are less understood. During a cruise campaign over the Chinese marginal sea (Bohai Sea), five low‐molecular‐weight aminiums were measured. The strong anthropogenic period (terrestrial transport) and the weak anthropogenic period (dust, clean, and sea fog periods) were identified based on the traceable aerosol chemical species, air masses transport patterns, and marine chlorophyll‐a. Inconsistent spatiotemporal variations of various aminiums were observed. Monomethylaminium (MMAH+), dimethylaminium (DMAH+), ethylaminium (EAH+), and diethylaminium (DEAH+) were more enriched during the weak anthropogenic period than the strong anthropogenic period and especially peaked during the sea fog period. The significant correlation between the four aminiums and methanesulfonic acid suggested their secondary formation pathways. Through further exploring the governing factors, the acid–base neutralization via the aqueous phase processing was identified as a critical process for the secondary transformation of aminiums. In contrast, trimethylaminium (TMAH+) showed moderate correlation with Na+ in the total suspended particles only, suggesting its primary marine sources via enrichment in the sea‐spray aerosol through bubble bursting. Based on the step‐wise correlation analysis, the sea surface organic nitrogenous reservoir was found as the dominant contributor to the measured aminiums over the Bohai Sea, while the role of marine phytoplankton emission in the formation of aminiums was limited. Plain Language Summary: Amines have been identified as key species in the formation processes of atmospheric particles, which may further have an impact on climate change. In the marine atmosphere, amines can be emitted from the seawater, while the emission pathway and formation mechanism of different amines are still unclear. It is also ambiguous whether the main contributor of amines over the ocean is dominated by the seawater organic nitrogenous reservoir or the marine phytoplankton emission. In this study, five common particulate aminiums were measured over the Bohai Sea. All aminiums largely originated from ocean during the weak anthropogenic influence period. However, inconsistent spatiotemporal variations and different correlations with some traceable atmospheric chemical components among various aminiums indicated their different emission pathways from the seawater, including seawater bubble bursting and air–sea exchange. For those amines emitted from the latter, the acid–base neutralization in the aqueous phase was identified as a critical process for the emitted gaseous amines to be transformed into their particulate phase. Besides, we found the seawater organic nitrogen reservoir as the dominant contributor to the measured aminiums, overwhelming the influence from the marine phytoplankton emission. Key Points: Atmospheric aminiums were emitted from the ocean through different pathways, that is, sea spray and secondary formationThe acid–base neutralization via the aqueous phase processing was critical for the secondary transformation of aminiumsThe sea surface organic nitrogenous reservoir was found as the dominant contributor to the measured aminiums over the Bohai Sea [ABSTRACT FROM AUTHOR]

The Arctic region is sensitive to climate change and is warming faster than the global average. Aerosol particles change cloud properties by acting as cloud condensation nuclei and ice-nucleating particles, thus influencing the Arctic climate system. Therefore, understanding the aerosol particle properties in the Arctic is needed to interpret and simulate their influences on climate. In this study, we collected ambient aerosol particles using whole-air and PM 10 inlets and residual particles of cloud droplets and ice crystals from Arctic low-level clouds (typically, all-liquid or mixed-phase clouds) using a counterflow virtual impactor inlet at the Zeppelin Observatory near Ny-Ålesund, Svalbard, within a time frame of 4 years. We measured the composition and mixing state of individual fine-mode particles in 239 samples using transmission electron microscopy. On the basis of their composition, the aerosol and cloud residual particles were classified as mineral dust, sea salt, K-bearing, sulfate, and carbonaceous particles. The number fraction of aerosol particles showed seasonal changes, with sulfate dominating in summer and sea salt increasing in winter. There was no measurable difference in the fractions between ambient aerosol and cloud residual particles collected at ambient temperatures above 0 ∘ C. On the other hand, cloud residual samples collected at ambient temperatures below 0 ∘ C had several times more sea salt and mineral dust particles and fewer sulfates than ambient aerosol samples, suggesting that sea spray and mineral dust particles may influence the formation of cloud particles in Arctic mixed-phase clouds. We also found that 43 % of mineral dust particles from cloud residual samples were mixed with sea salt, whereas only 18 % of mineral dust particles in ambient aerosol samples were mixed with sea salt. This study highlights the variety in aerosol compositions and mixing states that influence or are influenced by aerosol–cloud interactions in Arctic low-level clouds. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5) was monitored at five rural background locations in France from 2012 to 2021. Annual PM 2.5 ranged from 5 to 15 μg m−3, all sites repeatedly exceeding the 2021 annual World Health Organization guideline. Chemical speciation including organic and elemental carbon (OC, EC), secondary inorganic aerosols (SIA: NO 3 −, SO 4 2−, NH 4 +) and other major water-soluble ions (Cl−, Na+, Mg2+, Ca2+, K+) were monitored on 24-h filters covering 14% of the year. A source apportionment of OM was undertaken based on fine potassium and using representative ratios for domestic biomass burning (BB) and fossil fuel (FF) emissions. The latter dominated the EC fraction (55–60%) while BB was the main primary source of OM (27–54%). The average mass balance of PM 2.5 at the French rural background atmospheric sites was: secondary organic aerosol (18–35%), BB (17–27%), non-sea-salt sulphate (12–17%), nitrate (6–22%), ammonium (7–11%), FF (4–6%), mineral dust (3–9%) and sea salt (1–2%). Secondary aerosols were the main component of PM 2.5 through all seasons, with SIA dominating in spring episodes. The contribution of OM to PM 2.5 was larger at the southern sites whereas the contribution of SIA was larger at the northern sites. The mean OC/EC ratio and the good correlations between OC, EC, and fine potassium suggested that BB was the main primary source contributing to carbonaceous aerosols, 27–54% to total OM depending on the site; and also, to PM 2.5 (17–27%). Stronger regulations of OM sources including BB, nitrate from combustion, and ammonium from agricultural sources are needed to reduce PM 2.5 at rural background sites on an annual and episodic basis, respectively. [Display omitted] • PM 2.5 exceeded health guidelines at rural background sites in France in 2012–2021. • OM accounted for the largest PM 2.5 component followed by secondary inorganics. • Biomass burning is the main primary source of PM 2.5 : 17–27% of total PM 2.5 • Mitigation of nitrate and ammonium precursors required to reduce PM 2.5 levels. [ABSTRACT FROM AUTHOR]

The mass and light absorption contributions of organic carbon (OC), elemental carbon (EC), and mineral dust influence glacial melting and potentially contribute to climate change over the high Himalayas and Tibetan Plateau (HTP). Plateau-scale investigations of these components and their respective light absorption are limited due to the high altitude. In this study, we combined the analysis of major light-absorbing substances and their corresponding multiwavelength absorption to determine their specific contributions firstly. We investigated the spatial variations of total suspended particle (TSP) mass across the HTP, noting high contributions from dust, carbonaceous components, and secondary inorganic aerosols (SNA, including sulfate, nitrate, and ammonium). Enhanced levels of primary and secondary OC and SNA were observed in the marginal areas of the HTP, associated with high relative humidity (RH) and OX levels (O 3 +NO 2). EC was the primary contributor to light absorption, accounting for approximately 68%, 46%, and 64% in Ngari, Qinghai Lake, and Beiluhe, respectively. We found higher light-absorbing contributions from carbonaceous aerosols in the marginal areas compared to the central HTP site, particularly during the heating seasons (∼90%). Fugitive dust significantly contributed to TSP mass but not to light absorption. The concurrent constraints on the mass and optical properties of OC, EC, and dust in this study can help reduce uncertainties in climate models specific to the HTP. [Display omitted] • The dominant light-absorbing was attributed to EC in the HTP. • Enhanced carbonaceous aerosol light-absorbing contributions were obtained in the HTP margin area. • Fugitive dust was an important contributor to aerosol mass, while not for light absorption. [ABSTRACT FROM AUTHOR]

The study of the particle size distribution in the near-water aerosol, as well as suspended particulate matter (SPM) and organic compounds (OCs) in SPM in the surface waters of the South and Atlantic oceans showed that in the near-water atmosphere the minimum number of particles was found in the coastal regions of Antarctica due to the ice cover on the continent (for 0.3–1 μm particles, on average, 6182 particles/L). The maximum amount of aerosols (on average 28186, maximum 55389 particles/L) confined to coastal Europe is related to their influx from industrial areas and shipping. The latter led to a chaotic change in the concentrations of aerosols and OCs in surface waters (up to 70 μg/L, 214 μg/mg SPM for hydrocarbons in the English Channel). The fluxes from Patagonia and the African deserts lead to an increase of aerosols up to 33 824–34 893 particles/L, where they have the greatest effect, due to the mineral nature, on the SPM distribution in surface waters. The distribution of aerosols on the Africa–Antarctica section was mainly controlled by the frontal zones of surface waters; therefore, their content correlated with the speed of the wind blowing them out from the sea surface: r = 0.82. The La Plata River–Atlantic Ocean geochemical barrier affects the variability of the OCs and SPM concentrations in the surface water of the Montevideo area, where the SPM content varied from 0.23 to 1.3 mg/L, and HCs, from 7 to 48 μg/L (up to 37 μg/mg SPM). [ABSTRACT FROM AUTHOR]

Insufficient data on the chemical composition of PM2.5 and its emission sources in the southwestern (SW) Mediterranean area has been identified. Ambient PM2.5 samples were collected in an urban area of Tetouan city, northern Morocco. Chemical mass closure calculations and positive matrix factorization were performed for the comprehensive dataset of PM2.5 chemical analyses. Mass closure improved when multipliers (1.2 and 0.23, respectively) were used for the conversion of organic carbon (OC) and calcium ion (Ca2+) into particulate organic matter (POM) and mineral dust masses, respectively. The mass closure model performed well in this SW Mediterranean region, with a significant correlation (r2 = 0.97) obtained between gravimetrically measured and chemically determined PM2.5 mass. The one-year average concentration of PM2.5 was 17.96 μg/m3, and the major chemical components were POM (34%), secondary inorganic aerosol (SIA) (28%), and black carbon (18%), while unidentified mass was 4%. The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variations, with a summer-high and winter-low pattern for SIA, dust, and BC. In the winter months, POM was the dominant component. Source apportionment analysis revealed that PM2.5 emission sources, regarding their typical tracers, were ammonium sulfate (SO42−, NH4+, K+, NO3−), road traffic and biomass burning emissions (OC, BC), fresh sea salt (Cl−, K+, NO3−), aged sea salt (Mg2+, Na+, Ca2+), and oxalate-rich (oxalate, NO3−) factors. Further, it is hoped that these findings help to improve the scientific understanding of SW Mediterranean aerosols. [ABSTRACT FROM AUTHOR]

Aerosol vertical distribution generally determines their health impacts and climate effects. By using long‐term (2007–2019) CALIPSO lidar measurements, we present a large‐scale insight into the climatology of aerosol types and their vertical structure over East Asia. Despite the low sampling frequency, comparison with MODIS aerosol optical depth (AOD) shows that the integrated CAIPSO vertical extinction can reasonably reproduce spatial patterns of the aerosol loading. With the unique advantage of active detection, CALIPSO reveals an obvious enhancement of the night‐time AOD due to worse diffusion conditions. Moreover, long‐range transport of different aerosols including dust, polluted dust, and smoke has substantial contribution to the aerosol loading over East Asia. Pure dust particles are mainly concentrated over the deserts with notable dust transport belts (dust AOD > 0.2 at 532 nm) along downwind regions during winter and spring. By contrast, polluted dust is prevalent over the downstream eastern China with much higher AODs throughout the year. In particular, AOD of polluted dust (~0.5) is higher in winter rather than in spring, which is consistent with their seasonal occurrences. Smoke aerosols usually appear in the night‐time over southern China. The top heights of aerosols are around 4–6 km, with dust and smoke having higher extinction at upstream regions. The climatology of these aerosol types and vertical distribution can provide a significant constraint for associated studies of air quality and climate effects. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is one of the most important short-lived climate forcers, and atmospheric motions play an important role in determining its mass concentrations of pollutants. Here an intensive observation was launched in a typical river-valley city to investigate relationships between atmospheric motions and BC aerosols. Equivalent BC (e BC) source apportionment was based on an aethalometer model with the site-dependent absorption Ångström exponents (AAEs) and the mass absorption cross sections (MACs) retrieved using a positive matrix factorization (PMF) model based on observed chemical components (i.e., EC, POC, K + , Mg, Al, Si, S, Cl, Ca, V, Mn, Fe, Ni, Cu, As, Se, Br, Sr, Pb, Ga, and Zn) and primary absorption coefficients at selected wavelengths from λ=370 to 880 nm. The derived AAEs from 370 to 880 nm were 1.07 for diesel vehicular emissions, 2.13 for biomass burning, 1.74 for coal combustion, and 1.78 for mineral dust. The mean values for e BC fossil and e BC biomass were 2.46 and 1.17 µ g m -3 , respectively. Wind run distances and the vector displacements of the wind in 24 h were used to construct a self-organizing map, from which four atmospheric motion categories were identified (local-scale dominant, local-scale strong and regional-scale weak, local-scale weak and regional-scale strong, and regional-scale dominant). BC pollution was found to be more likely when the influence of local-scale motions outweighed that of regional-scale motions. Cluster analysis for the back-trajectories of air mass calculated by the Hybrid Single-Particle Lagrangian Integrated Trajectory model at the study site indicated that the directions of air flow can have different impacts for different scales of motion. The direct radiative effects (DREs) of source-specific e BC were lower when the influence of regional-scale motions outweighed that of the local ones. However, due to chemical aging of the particles during transport – the DRE efficiencies under regional-scale motions were ∼ 1.5 times higher than those under more local influences. The finding that the DRE efficiency of BC increased during the regional transport suggested significant consequences in regions downwind of pollution sources and emphasizes the importance of regionally transported BC for potential climatic effects. [ABSTRACT FROM AUTHOR]

Atmospheric deposition is one of the main sources of dissolved iron (Fe) in the ocean surfaces. Atmospheric processes are recognized as controlling fractional Fe solubility (Fe sol %) in marine aerosol particles. However, the impact of these processes on Fe sol % remains unclear. One of the reasons for this is the lack of field observations focusing on the relationship between Fe sol % and Fe species in marine aerosol particles. In particular, the effects of organic ligands on Fe sol % have not been thoroughly investigated in observational studies. In this study, Fe species in size-fractionated aerosol particles in the Pacific Ocean were determined using X-ray absorption fine structure (XAFS) spectroscopy. The internal mixing states of Fe and organic carbon were investigated using scanning transmission X-ray microscopy (STXM). The effects of atmospheric processes on Fe sol % in marine aerosol particles were investigated based on the speciation results. Iron in size-fractionated aerosol particles was mainly derived from mineral dust, regardless of aerosol diameter, because the enrichment factor of Fe was almost 1 in both coarse (PM >1.3) and fine aerosol particles (PM 1.3). Approximately 80 % of the total Fe (insoluble + labile Fe) was present in PM >1.3 , whereas labile Fe was mainly present in PM 1.3. The Fe sol % in PM >1.3 was not significantly increased (2.56±2.53 %, 0.00 %–8.50 %, n=20) by the atmospheric processes because mineral dust was not acidified beyond the buffer capacity of calcite. In contrast, mineral dust in PM 1.3 was acidified beyond the buffer capacity of calcite. As a result, Fe sol % in PM 1.3 (0.202 %–64.7 %, n=10) was an order of magnitude higher than that in PM >1.3. The PM 1.3 contained ferric organic complexes with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes), and the abundance correlated with Fe sol %. Iron(III)-HULIS was formed during transport in the Pacific Ocean because Fe(III)-HULIS was not found in aerosol particles in Beijing and Japan. The pH estimations of mineral dust in PM 1.3 established that Fe was solubilized by proton-promoted dissolution under highly acidic conditions (pH < 3.0), whereas Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be reproduced by proton-promoted dissolution under moderately acidic conditions, the pH of mineral dust increased after proton-promoted dissolution. The cloud process in the marine atmosphere increases the mineral dust pH because the dust particles are covered with organic carbon and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS owing to its high water solubility. Thus, the organic complexation of Fe with HULIS plays a significant role in the stabilization of Fe that was initially solubilized by proton-promoted dissolution. [ABSTRACT FROM AUTHOR]

Environmental context: We present a chemical characterisation of the seasonal snowpack sampled for four consecutive years at the Calderone, the southernmost glacier still surviving in peninsular Italy. This debris covered glacier recently split into two little ice bodies, whose evolution could be influenced by the snowpack properties. In particular the impact of long-range aerosol advections on concentrations of impurities in the snowpack over the local background is discussed. Rationale: The Calderone Glacier (Central Apennine, Gran Sasso d'Italia mountain group) is the southernmost glacial apparatus in Europe, split into two glacierets (Upper and Lower Calderone) since the end of the last millennium. Because of its location and altitude, this site is mainly characterised by the long-range transport of air masses which arise from different Mediterranean source regions. Therefore, the seasonal snowpack's chemistry is strongly affected by the dry and wet deposition of contaminants associated with anthropogenic and natural sources. Methodology: In the present study, the seasonal snowpack stratified on the Calderone glacier has been characterised for four consecutive years (2017–2020) in the same monitoring site (2700 m asl), where a snow pit has been dug yearly, to observe the modification of chemical and physical properties depending on local and long-range atmospheric contributions. We determined the concentrations and fluxes of major inorganic ions (MIs) by ion chromatography and of 31 trace elements (TEs) by triple quadrupole ICP-MS. Results: Major and trace element concentration profiles along the snowpack allowed to discriminate the snow layers contaminated by long range advections from the uncontaminated ones. The uncontaminated snow layers' concentrations were used to calculate regional background values. The results have been compared to other remote sites to assess their robustness. Discussion: Different source contributions have been recognised using enrichment factors for the trace elements, particularly crustal, marine and anthropogenic. Deposited atmospheric aerosols, found in the snowpack as distinct layers generated during intense air mass advections, have been correlated to these contributions. Environmental context. We present a chemical characterisation of the seasonal snowpack sampled for four consecutive years at the Calderone, the southernmost glacier still surviving in peninsular Italy. This debris covered glacier recently split into two little ice bodies, whose evolution could be influenced by the snowpack properties. In particular the impact of long-range aerosol advections on concentrations of impurities in the snowpack over the local background is discussed. [ABSTRACT FROM AUTHOR]

Due to the complexity of emission sources, a better understanding of aerosol optical properties is required to mitigate climate change in China. Here, an intensive real-time measurement campaign was conducted in an urban area of China before and during the COVID-19 lockdown in order to explore the impacts of anthropogenic activities on aerosol light extinction and the direct radiative effect (DRE). The mean light extinction coefficient (bext) decreased from 774.7 ± 298.1 Mm -1 during the normal period to 544.3 ± 179.4 Mm -1 during the lockdown period. A generalised additive model analysis indicated that the large decline in bext (29.7 %) was due to sharp reductions in anthropogenic emissions. Chemical calculation of bext based on a ridge regression analysis showed that organic aerosol (OA) was the largest contributor to bext in both periods (45.1 %–61.4 %), and the contributions of two oxygenated OAs to bext increased by 3.0 %–14.6 % during the lockdown. A hybrid environmental receptor model combined with chemical and optical variables identified six sources of bext. It was found that bext from traffic-related emissions, coal combustion, fugitive dust, the nitrate and secondary OA (SOA) source, and the sulfate and SOA source decreased by 21.4 %–97.9 % in the lockdown, whereas bext from biomass burning increased by 27.1 %, mainly driven by the undiminished need for residential cooking and heating. An atmospheric radiative transfer model was further used to illustrate that biomass burning, rather than traffic-related emissions, became the largest positive effect (10.0 ± 10.9 W m -2) on aerosol DRE in the atmosphere during the lockdown. Our study provides insights into aerosol bext and DRE from anthropogenic sources, and the results imply the importance of controlling biomass burning for tackling climate change in China in the future. [ABSTRACT FROM AUTHOR]

The impact of the aerosol optical properties on the ultraviolet index (UVI) in the urban area of Rome is investigated in this study. In particular, the influence of aerosol optical depth (AOD) and single scattering albedo (SSA), estimated at the wavelength of 340 nm, and of the Ångström exponent, calculated in the range 340–500 nm, over a period of 11 years (2010–2020) in the months from March to September are analyzed. The UVI is monitored by a Brewer spectrophotometer, whereas measurements of the direct Sun and diffuse sky irradiances are performed by a co-located PREDE-POM sun–sky radiometer of the ESR/SKYNET network; the aerosol optical properties are obtained by the Skyrad MRIv2 retrieval. A novel method, based on physical principles and easily adaptable to other contexts, is developed to extrapolate the aerosol properties to the UV range during periods when only visible to near-infrared measurements are available. The retrievals from the sun–sky radiometer are consistent with the chemical characterization of urban PM 10 (particulate matter 10 mm or less in diameter) samples collected during an intensive field campaign held in summer 2011 at the same site (URBan Sustainability Related to Observed and Monitored Aerosol – URBS ROMA). The PM macro components identified during the campaign are grouped in order to evaluate the contribution of the main macro sources (soil, sea, secondary inorganic, organics, and traffic) whose relative role is indeed expected to strongly affect the aerosol absorption capability. The surface forcing efficiency, calculated as the change in the UV index for a unit AOD variation, shows that AOD is the primary parameter affecting the surface irradiance under clear-sky conditions in Rome. SSA and the Ångström exponent are also identified as secondary influencing factors, i.e., the surface forcing efficiency is found to be greater for smaller zenith angles and for larger and more absorbent particles in the UV range (such as, e.g., mineral dust). [ABSTRACT FROM AUTHOR]

The spatiotemporal variations in free-cellulose concentrations in atmospheric particles, as a proxy for plant debris, were investigated using an improved protocol with a high-performance liquid chromatography with pulsed amperometric detection (HPLC-PAD) method. Filter samples were taken from nine sites of varying characteristics across France and Switzerland, with sampling covering all seasons. Concentrations of cellulose, as well as carbonaceous aerosol and other source-specific chemical tracers (e.g. elemental carbon, EC; levoglucosan; polyols; trace metals; and glucose), were quantified. Annual mean free-cellulose concentrations within PM 10 (particulate matter) ranged from 29 ± 38 ng m -3 at Basel (urban site) to 284 ± 225 ng m -3 at Payerne (rural site). Concentrations were considerably higher during episodes, with spikes exceeding 1150 and 2200 ng m -3 at Payerne and ANDRA-OPE (Agence nationale pour la gestion des déchets radioactifs Observatoire Pérenne de l'Environnement; rural site), respectively. A clear seasonality, with highest cellulose concentrations during summer and autumn, was observed at all rural and some urban sites. However, some urban locations exhibited a weakened seasonality. Contributions of cellulose carbon to total organic carbon are moderate on average (0.7 %–5.9 %) but much greater during "episodes", reaching close to 20 % at Payerne. Cellulose concentrations correlated poorly between sites, even at ranges of about 10 km, indicating the localised nature of the sources of atmospheric plant debris. With regards to these sources, correlations between cellulose and typical biogenic chemical tracers (polyols and glucose) were moderate to strong (Rs = 0.28–0.78, p < 0.0001) across the nine sites. Seasonality was strongest at sites with stronger biogenic correlations, suggesting the main source of cellulose arises from biogenic origins. A second input to ambient plant debris concentrations was suggested via resuspension of plant matter at several urban sites, due to moderate cellulose correlations with mineral dust tracers, Ca 2+ , and Ti metal (Rs = 0.28–0.45, p < 0.007). No correlation was obtained with the biomass burning tracer (levoglucosan), an indication that this is not a source of atmospheric cellulose. Finally, an investigation into the interannual variability in atmospheric cellulose across the Grenoble metropole was completed. It was shown that concentrations and sources of ambient cellulose can vary considerably between years. All together, these results deeply improve our knowledge on the phenomenology of plant debris within ambient air. [ABSTRACT FROM AUTHOR]

Cross-country assessment of aerosol loading was made over several South Asian megacities using multiple high-resolution remote-sensing database to assess how aerosols vary within the city and its suburbs. Parameters sensitive to aerosol optical and microphysical properties were processed over city-core and its surrounding, separated by a buffer. Cities across the Indo-Gangetic Plain (IGP; AOD:0.52–0.72) along with Mumbai (0.47) and Bangalore (0.46) denote comparatively high aerosol loading against non-IGP cities. City-core specific AOD was invariably high compared to surrounding, however with varying gradient having robust geographical signature. Exceptions to this general trend were in Kathmandu (ΔAOD: 0.07) and Dhaka (ΔAOD: 0.01) while strong positive AOD gradient was noted in Bangalore (+0.11), Colombo (+0.08) and in Mumbai (+0.07). While all mainland cities exhibited robust intraannual variability, distinction between city-core and its surrounding AOD exhibited varying seasonality. City-specific geometric coefficient of variation indicated insignificant association with mean AOD as opposed to European and American cities. Both pixel-based and city-specific analysis revealed a strong increasing trend in AOD with highest magnitude in Varanasi and Bangalore. Aerosol sub-types based on aerosols' sensitivity to UV-absorption and particle size denotes higher relative abundance of carbonaceous smoke aerosols within city-core, without having significant distinction for mineral dusts and urban aerosols. Micro-scale variations in columnar aerosols and aerosol subtypes over South Asian cities. [Display omitted] • Majority of South Asian cities are more polluted at city-core compared to its suburbs. • Robust aerosol gradient from city-core to its suburbs in Bangalore, Colombo, Mumbai. • Core region of Kathmandu and Dhaka city frequently receive aerosols from its suburbs. • Spatial variations in aerosol sub-types were less sensitive for dust & urban aerosols. • Carbonaceous smoke aerosols were more abundant at city-core with high UV-absorption. [ABSTRACT FROM AUTHOR]

A comprehensive study on the regional and spatial distributions of aerosol columnar optical and physical characteristics utilizing high-quality Aerosol Robotic Network (AERONET) datasets over Asia (Central, South, South-East, and East Asia), along with spatiotemporal collocated validation of two highly-spatially resolved models (Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) and Copernicus Atmosphere Monitoring Service (CAMS)) simulated aerosol optical depth (AOD) and Ångström exponent (AE) on annual and seasonal scales, is conducted for the first time. AOD is the highest over South Asia in each season, followed by South-East, East, and Central Asia. Annual regional average AOD at 0.50 μm over South Asia is 0.61. Combined influence of both fine mode anthropogenic aerosol emissions from fossil fuel combustion and biomass burning, and coarse mode dust aerosols from seasonal transport lead to higher AOD and total volume concentration (TVC), and exhibit significant spatiotemporal variations. Coarse volume fraction (CVF) and effective radius (R eff) are higher over Central Asia due to the dominance of coarse dust aerosols. East and South-East Asia are dominated by fine mode aerosols and result in higher fine volume concentration (FVC), AE, fine mode fraction (FMF), and lower R eff. Compared to the other regions of the globe (except Africa), AOD is higher over Asia, with higher spatiotemporal variabilities in AOD, AE, FMF, and TVC. Over Asia, the agreement between AERONET and CAMS AOD is better than that of AERONET and MERRA-2 AOD. For high AOD conditions, underestimation in model AODs is higher, and lower fraction of model AODs satisfy the Global Climate Observing System (GCOS) requirement over all regions, and these are more pronounced over Asia. Biases in model AODs are higher over Asia compared to the other regions of the globe, and lower over North America, Europe, and Australia. Higher bias in model AEs compared to AODs over all the regions shows substantial challenges in simulating spectral AOD and appropriate contributions of fine and coarse mode aerosols. These findings over a global aerosol hotspot region, Asia, along with other regions of the globe are crucial for accurate simulation and fine-tuning of aerosol characteristics by regional and global models, and for reducing uncertainties in the assessment of radiative and climate impact of aerosols. [Display omitted] • Aerosol optical depth (AOD) and total volume concentration (VC) are the highest in South Asia. • High fine VC and low effective radius are observed over South-East and East Asia. • Spatiotemporal variations in AOD and size distribution are higher in Asia over the globe. • The performance of CAMS is better than MERRA-2 in capturing AERONET AOD over Asia. • Biases in MERRA-2 and CAMS AODs are higher in Asia compared to other regions of globe. [ABSTRACT FROM AUTHOR]

Measurements of absorption coefficients (σ ap , λ) and carbonaceous components (OC, EC, WSOC and levoglucosan) in PM 1 were conducted at an urban background site in southeastern Spain throughout 2021. The main goal of this research was to determine the contribution from different sources to WSOC light absorption (σ WSOC). For this, σ BrC , λ values were previously obtained. The mean contribution of BrC to total aerosol absorption was ∼29% at 370 nm, revealing a significant influence of BrC to light absorption in the study area. Assuming that BrC light absorption was from WSOC and WIOC, a multilinear regression (MLR) model was used to estimate σ WSOC and σ WIOC. Average values (mean ± SD) were very similar for both components: σ WSOC,370 = 1.6 (±0.7) Mm−1 and σ WIOC,370 = 1.9 (±0.7) Mm−1. Finally, the PMF technique coupled with MLR analysis was used to identify the sources of WSOC light absorption and estimate their contribution. Our findings point to biomass burning as the dominant source of σ WSOC during the cold season, with a contribution of ∼37%. The Mineral Dust and Secondary Nitrate sources, that were not included in the model due to their low contribution to WSOC mass concentrations, accounted for a significant percentage of σ WSOC during this period. Secondary organic aerosol was the major source during the warm season (∼56%), followed by traffic emissions (∼30%). • Sources of WSOC absorption was analysed at an urban background site in the southeast of the Iberian Peninsula. • BrC accounted for 29% of the total aerosol absorption at 370 nm, with similar contributions from WSOC and WIOC. • Marked seasonal variation of WSOC absorption, with higher levels during the cold season when BB emissions are highest. [ABSTRACT FROM AUTHOR]

We present a climatological study of aerosols in four representative Caribbean Sea islands that is based on daily mean values of aerosol optical properties for the period 2008-16, using the aerosol optical depth (AOD) and Ångstr from exponent (AE) to classify the dominant aerosol type. A climatological assessment of the spatiotemporal distribution of the main aerosol types, their links with synoptic patterns, and the transport from different sources is provided. Maximum values of AOD occur in the rainy season, coinciding with the minimum in AE and an increased occurrence of dust, whereas the minimum of AOD occurs in the dry season, due to the predominance of marine aerosols. Marine and dust aerosol are more frequent in the easternmost islands and decrease westward because of an increase of continental and mixture dust aerosols. Therefore, the westernmost station displays the most heterogeneous composition of aerosols. Using a weather-type classification, we identify a quantifiable influence of the atmospheric circulation in the distribution of Caribbean aerosols. However, they can occur under relatively weak and/or diverse synoptic patterns, typically involving transient systems and specific configurations of the Azores high that depend on the considered station. Backward trajectories indicate that dry-season marine aerosols and rainy-season dust are transported by air parcels traveling within the tropical easterly winds. The main source region for both types of aerosols is the subtropical eastern Atlantic Ocean, except for Cuba, where the largest contributor to dry-season marine aerosols is the subtropical western Atlantic. Different aerosol types follow similar pathways, suggesting a key role of emission sources in determining the spatiotemporal distribution of Caribbean aerosols. [ABSTRACT FROM AUTHOR]

The study presents a climatology of aerosol composition concentration obtained by a recently developed GRASP/Component (GRASP stands for the Generalized Retrieval of Atmosphere and Surface Properties algorithm) approach applied to the whole archive of POLDER-3 observations. The conceptual specific of the GRASP/Component approach is in direct retrieval of aerosol speciation (component fraction) without an intermediate retrievals of aerosol optical characteristics. Despite a global validation of the derived aerosol component product is challenging, the results obtained are in line with general knowledge about aerosol types in different regions. In addition, we compare the GRASP derived black carbon and dust components with those of the MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) product. Quite reasonable general agreement in spatial and temporal distribution of the species provided by GRASP and MERRA-2 was found, the differences however appeared in regions known for strong biomass burning and dust emissions; the reasons for the discrepancies are discussed. The other derived components, such as concentration of absorbing (black carbon, brown carbon, iron oxides content in mineral dust) and scattering (ammonium sulphate and nitrate, organic carbon, non-absorbing dust) aerosol, represent scarce but imperative information for validation and potential adjustment of chemical transport models. The aerosol optical properties derived by GRASP/Component were found to agree well with the AERONET ground reference data and fully consistent with the previous GRASP Optimized, High Precision and Models retrieval versions applied to POLDER-3 data. Thus, the presented extensive climatology product provides an opportunity for understanding variabilities and trends in global and regional distributions of aerosol species. The climatology of the aerosol components obtained in addition to the aerosol optical properties provides additional valuable, qualitatively new inside about aerosol distributions and, therefore, demonstrates advantages of multi-angular polarimetric satellite observations as the next frontier for aerosol inversion from advanced satellite observations. [ABSTRACT FROM AUTHOR]

The aerosols play an important role in the modification of the regional radiation budget. Long-term trend analysis of properties of atmospheric aerosols is important for policymakers and also for the study of the climatic implications. The Aerosol Robotic Network (AERONET) provides continuous ground-truth aerosol data during cloud-free days since two decades in India. Long-term atmospheric aerosol properties have been studied over four different sites of Indo-Gangetic Plain (IGP): Gandhi College rural background, Kanpur, urban and highly industrial area, Jaipur urban and desert dust influenced region, and Lahore urban and agriculture rich region respectively using AERONET data. The yearly variation of aerosol optical depth (AOD) along with angstrom exponent (AE), single scattering albedo (SSA), size distribution parameters (volume concentration and effective radius), and aerosol radiative forcing (ARF) have been analyzed for nine years from 2009 to 2017. A positive trend of AOD over Kanpur (0.0074/year), a negative trend over Lahore (−0.0054/year), Jaipur – 0.0027/year) and Gandhi college (−0.0008/year) was found. Volume concentration shows the increasing trend of fine mode particles which may be due to increased anthropogenic activities in comparison to natural aerosols over Kanpur, Lahore, Gandhi College, and Jaipur respectively. SSA values over Kanpur and Jaipur show dominancy of scattering while absorbing nature of particles over Lahore and Gandhi College were found. The trend of total atmospheric radiative forcing (ARF ATM) over Kanpur and Jaipur locations was found to be decreased slightly but not so significantly while over Lahore and Gandhi College trend was found to increase in a significant way. The yearly trend of ARF ATM over Kanpur, Lahore, Jaipur, and Gandhi College was found to be −0.76 Wm−2 /year, 2.22 Wm−2 /year, −0.08 Wm−2 /year, and 3.09 Wm−2 /year respectively. [ABSTRACT FROM AUTHOR]

In the Aerosol Robotic Network (AERONET) aerosol retrieval algorithm, smoothness constraints on the imaginary part of the refractive index (IPRI) provide control of retrieved spectral dependence of aerosol absorption by preventing the inversion code from fitting the noise in optical measurements and thus avoiding unrealistic oscillations of retrievals with wavelength. The history of implementation of the IPRI smoothness constraints in the AERONET aerosol retrieval algorithm is discussed. It is shown that the latest version of the IPRI smoothness constraints, termed standard (STD) and employed by Version 3 (V3) of aerosol retrieval algorithm, should be modified to account for strong variability of light absorption by brown carbon (BrC) containing aerosols in UV through mid-visible parts of the solar spectrum. In V3 strong spectral constraints were imposed at high values of the Angstrom Exponent (AE; 4 40-870 nm) since black carbon (BC) was assumed to be the primary absorber, while the constraints became increasingly relaxed as AE deceased to allow f or wavelength dependence of absorption for dust aerosols. The new version of the IPRI smoothness constraints assigns different weights to different pairs of wavelengths which are the same for all values of the Angstrom Exponent. For example, in the case of four wavelength input, the weights assigned to short wavelength pairs (440-675, 675-870 nm) are small (10-6) so that smoothness constraints do not suppress natural spectral variability of the IPRI. At longer wavelengths (870-1020 nm), however, the weight is ten times higher to provide additional constraints on the IPRI retrieval s of aerosols with high AE due to low sensitivity to aerosol absorption for longer channels at relatively low aerosol optical depths for these fine mode dominated aerosols. The effect of applying the new version of the IPRI smoothness constraints, termed relaxed (REL), on retrievals of single scattering albedo (SSA) is analysed for case studies of different aerosol types: BC and BrC containing fin e mode aerosols, mineral dust coarse mode aerosols and urban industrial fine mode aerosol. It is shown that for BrC containing aerosols employing the REL smoothness constraints resulted in significant reduction, compared to STD, in retrieved SSA and spectral residual errors at the short wavelengths. For example, biomass burning smoke cases show a reduction in SSA and spectral residual at 380 nm is ~0.033 and ~17 % respectively for the Rexburg site and ~0.04 and ~12.7 % for the Rimrock site, both AERONET sites in Idaho, USA. For a site with very high levels of BC containing aerosols (Mongu, Zambia) the effect of modification in the IPRI smoothness constraints is minor. For mineral dust aerosols at small AE values (Mezaira site, UAE) the spectral constraint on IPRI was already relaxed in V3 therefore the new REL constraint results in minimal change. In the case of weakly absorbing urban industrial aerosols at the GSFC site, there are significant changes in retrieved SSA using the REL assumption, especially reductions at longer wavelengths: ~ 0.016 and ~0.02 at 875 and 1020 nm respectively for 440 nm AOD ~0.3. Comparison of aerosol parameters retrieved by inversion using STD and REL assumptions is presented. Analysis is done for retrievals utilizing the four standard AERONET wavelengths obtained at four AERONET sites: Rexburg, Mongu, Mezaira, and GSFC. The largest difference is found for the IPRI retrievals for BrC containing biomass burning (Rexburg) and urban industrial (GSFC) aerosols in which cases employing the STD assumption in the AERONET inversion was over constraining the spectral dependence of the IPRI. The modification of smoothness constraints on the IPRI has a minor effect on retrievals of other aerosol parameters such as the real part of refractive index and parameters of the aerosol size distribution. Both SSA retrieved using STD and REL assumptions were compared to SSA derived from in situ measurements collected during the DRAGON-MD field campaign in 2011. The DISCOVER-AQ column-integrated in situ aircraft SSA data for 550 nm were compared to AERONET retrievals at 440 nm and 675 nm which were interpolated to 500 nm and showed a closer agreement between in situ SSA and SSA retrieved from inversions employing the REL assumption than between in situ SSA and SSA retrieved using STD constraints. The implementation of the relaxed smoothness constraints on the imaginary part of the refractive in the next version of the AERONET inversion algorithm will produce significant impacts at some sites with changes u p to ±0.033 and ±0.017 in short wavelength channels (380 nm and 440 nm) for some biomass burning smoke cases with significant BrC content and possibly up to ±0.015 in mid-visible channels (500 nm and 675 nm) to near IR channels (870 nm to 1020 nm) for some urban industrial aerosol types while still mostly within the uncertainty of the AERONET SSA retrievals, depending on AOD level, Angstrom Exponent and wavelength. For mineral dust aerosols the impact will be insignificant, while for biomass burning aerosol dominated by BC the changes will be relatively small. [ABSTRACT FROM AUTHOR]

The year of 2015 was an extremely dry year for Southeast Asia where the direct impact of a strong El Niño was in play. As a result of this dryness and the relative lack of rainfall, an extraordinary quantity of aerosol particles from biomass burning remained in the atmosphere over the Maritime Continent during the fire season. This study uses the Weather Research and Forecasting model coupled with Chemistry to understand the impacts of these fire particles on cloud microphysics and radiation during the peak biomass burning season in September. Our simulations, one with fire particles and the other without them, cover the entire Maritime Continent region at a cloud-resolving resolution (4 km) for the entire month of September in 2015. The comparison of the simulations shows a clear sign of precipitation enhancement by fire particles through microphysical effects; smaller cloud droplets remain longer in the atmosphere to later form ice crystals, and/or they are more easily collected by ice-phase hydrometeors in comparison to droplets under no fire influences. As a result, the mass of ice-phase hydrometeors increases in the simulation with fire particles, and so does rainfall. On the other hand, the aerosol radiative effect weakly counteracts the invigoration of convection. Clouds are more reflective in the simulation with fire particles as ice mass increases. Combined with the direct scattering of sunlight by aerosols, the simulation with fire particles shows higher albedo over the simulation domain on average. The simulated response of clouds to fire particles in our simulations clearly differs from what was presented by two previous studies that modeled aerosol–cloud interaction in years with different phases of El Niño–Southern Oscillation (ENSO), suggesting a further need for an investigation on the possible modulation of fire–aerosol–convection interaction by ENSO. [ABSTRACT FROM AUTHOR]

The aim of this study was to characterize the physicochemical properties and microbial communities of particulate matter (PM) in Seoul, Korea. We collected long-term (2017–2019) precipitation samples and PM10 and PM2.5 monitoring data to determine the impact of soluble and insoluble chemical species on the soil surface. Ambient PM10 concentrations were higher than PM2.5 concentrations during the monitoring period, but both decreased during rainfall due to the washing effect of precipitation. PM2.5 particles had a "fluffy" shape and contained sulfur (0.2%), but suspended particles (SPs) contained many carbon particles (approximately 60%). Spherical particles containing metal oxides, Fe and Al, might be originated from coal combustion, wild fires, and metal-refining processes under high-temperature conditions. Dissolved ions in precipitation included those eluted from salts and coal combustion based on the correlation coefficients of Na and Cl (R = 0.953) and F and NO3 (R = 0.706). The δ15N–NO3 and δ34S–SO4 of precipitation were enriched as the atmospheric temperature decreased from 9.8 to −1.6°C, implying the influence of domestic coal combustion. Backward trajectories showed that, in winter, air parcels passed through industrialized cities from China to South Korea. The microbial communities associated with PM were strongly influenced by atmospheric conditions. Proteobacteria (range from 4.6 to 76.7%) and Firmicutes (range from 6.0 to 91.4%) were the most dominant phyla and were significantly affected by changes in the PM2.5 environment. The results indicate that the acidity of precipitation and the composition of aerosols were affected by fossil fuel combustion and mineral dust, and that atmospheric conditions may change as PM2.5 concentrations increase. [ABSTRACT FROM AUTHOR]

Spatial and temporal variability of aerosol optical depth (AOD) together with aerosol-type specification were analyzed over Eastern Province of Kingdom of Saudi Arabia (KSA) and Bahrain from 2008 to 2019. To investigate study region with more details, the Eastern Province of Saudi Arabia and Bahrain was divided into three and four zones, respectively. This work utilized comprehensive satellite-based air quality data using NASA's Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) model. The retrieved total AOD data exhibited relatively lower average values in the Bahraini zones in comparison with the Eastern KSA during the study period. The monthly total AOD values in Bahraini zones were in the range of 0.20 and 0.87, while they were in the range of 0.23 and 0.91 in KSA zones. The AOD values were positively correlated with ambient air temperature (r = 0.43), while they were negatively correlated with relative humidity (r = 0.59) in Bahrain. Seasonal wind rose diagrams for Bahrain and monthly synoptic maps of (20–40°N, 40–60°E) West Asia region demonstrates that dominant wind direction is from NNW to Bahrain. The data assimilation algorithms in MERRA-2 showed that the major aerosol species that contributed to total AOD were as follows: mineral dust (68–74%), sulfate (17–20%), organic carbon (4–5%), sea salt (3–5%) and black carbon (2%). Monthly, seasonal and annual variations of speciated AOD values assisted in understanding aerosols loading over study area. [ABSTRACT FROM AUTHOR]

Biomass burning smoke is advected over the southeastern Atlantic Ocean between July and October of each year. This smoke plume overlies and mixes into a region of persistent low marine clouds. Model calculations of climate forcing by this plume vary significantly in both magnitude and sign. NASA EVS-2 (Earth Venture Suborbital-2) ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) had deployments for field campaigns off the west coast of Africa in 3 consecutive years (September 2016, August 2017, and October 2018) with the goal of better characterizing this plume as a function of the monthly evolution by measuring the parameters necessary to calculate the direct aerosol radiative effect. Here, this dataset and satellite retrievals of cloud properties are used to test the representation of the smoke plume and the underlying cloud layer in two regional models (WRF-CAM5 and CNRM-ALADIN) and two global models (GEOS and UM-UKCA). The focus is on the comparisons of those aerosol and cloud properties that are the primary determinants of the direct aerosol radiative effect and on the vertical distribution of the plume and its properties. The representativeness of the observations to monthly averages are tested for each field campaign, with the sampled mean aerosol light extinction generally found to be within 20 % of the monthly mean at plume altitudes. When compared to the observations, in all models, the simulated plume is too vertically diffuse and has smaller vertical gradients, and in two of the models (GEOS and UM-UKCA), the plume core is displaced lower than in the observations. Plume carbon monoxide, black carbon, and organic aerosol masses indicate underestimates in modeled plume concentrations, leading, in general, to underestimates in mid-visible aerosol extinction and optical depth. Biases in mid-visible single scatter albedo are both positive and negative across the models. Observed vertical gradients in single scatter albedo are not captured by the models, but the models do capture the coarse temporal evolution, correctly simulating higher values in October (2018) than in August (2017) and September (2016). Uncertainties in the measured absorption Ångstrom exponent were large but propagate into a negligible (<4 %) uncertainty in integrated solar absorption by the aerosol and, therefore, in the aerosol direct radiative effect. Model biases in cloud fraction, and, therefore, the scene albedo below the plume, vary significantly across the four models. The optical thickness of clouds is, on average, well simulated in the WRF-CAM5 and ALADIN models in the stratocumulus region and is underestimated in the GEOS model; UM-UKCA simulates cloud optical thickness that is significantly too high. Overall, the study demonstrates the utility of repeated, semi-random sampling across multiple years that can give insights into model biases and how these biases affect modeled climate forcing. The combined impact of these aerosol and cloud biases on the direct aerosol radiative effect (DARE) is estimated using a first-order approximation for a subset of five comparison grid boxes. A significant finding is that the observed grid box average aerosol and cloud properties yield a positive (warming) aerosol direct radiative effect for all five grid boxes, whereas DARE using the grid-box-averaged modeled properties ranges from much larger positive values to small, negative values. It is shown quantitatively how model biases can offset each other, so that model improvements that reduce biases in only one property (e.g., single scatter albedo but not cloud fraction) would lead to even greater biases in DARE. Across the models, biases in aerosol extinction and in cloud fraction and optical depth contribute the largest biases in DARE, with aerosol single scatter albedo also making a significant contribution. [ABSTRACT FROM AUTHOR]

Field measurements were conducted to determine aerosol chemical composition at a newly established remote high-altitude site in North Africa at the Atlas Mohammed V (AMV) atmospheric observatory located in the Middle Atlas Mountains. The main objectives of the present work are to investigate the variations in the aerosol composition and better assess global and regional changes in atmospheric composition in North Africa. A total of 200 particulate matter (PM 10) filter samples were collected at the site using a high-volume (HV) collector in a 12 h sampling interval from August to December 2017. The chemical composition of the samples was analyzed for trace metals, water-soluble ions, organic carbon (OC/EC), aliphatic hydrocarbons, and polycyclic aromatic hydrocarbon (PAH) contents. The results indicate that high-altitude aerosol composition is influenced by both regional and transregional transport of emissions. However, local sources play an important role, especially during low wind speed periods, as observed for November and December. During background conditions characterized by low wind speeds (avg. 3 m s -1) and mass concentrations in the range from 9.8 to 12 µ g m -3 , the chemical composition is found to be dominated by inorganic elements, mainly suspended dust (61 %) and ionic species (7 %), followed by organic matter (7 %), water content (12 %), and unidentified mass (11 %). Despite the proximity of the site to the Sahara, its influence on the atmospheric composition at this high-altitude site was mainly seasonal and accounted for only 22 % of the sampling duration. Biogenic organics contributed up to 7 % of the organic matter with high contributions from compounds such as heneicosane, hentriacontane, and nonacosane. The AMV site is dominated by four main air mass inflows, which often leads to different aerosol chemical compositions. Mineral dust influence was seasonal and ranged between 21 % and 74 % of the PM mass, with peaks observed during the summer, and was accompanied by high concentrations of SO 42- of up to 3.0 µ g m -3. During winter, PM 10 concentrations are low (<30 µ g m -3), the influence of the desert is weaker, and the marine air masses (64 %) are more dominant with a mixture of sea salt and polluted aerosol from the coastal regions (Rabat and Casablanca). During the daytime, mineral dust contribution to PM increased by about 42 % because of road dust resuspension. In contrast, during nighttime, an increase in the concentrations of alkanes, PAHs, alkane-2-ones, and anthropogenic metals such as Pb, Ni, and Cu was found due to variations in the boundary layer height. The results provide the first detailed seasonal and diurnal variation of the aerosol chemical composition, which is valuable for long-term assessment of climate and regional influence of air pollution in North Africa. [ABSTRACT FROM AUTHOR]

In this study we present the seasonal chemical characteristics and potential sources of PM10 at an urban location of Delhi, India during 2010˗2019. The concentrations of carbonaceous aerosols [organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC) and water insoluble organic carbon (WIOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Pb, Cr, F, Cl, Br, P, S, K, As, Na, Mg, Ca, B, Ni, Mo, V, Sr, Zr and Rb) in PM10 were estimated to explore their possible sources. The annual average concentration (2010–2019) of PM10 was computed as 227 ± 97 µg m−3 with a range of 34˗734 µg m−3. The total carbonaceous aerosols in PM10 was accounted for 22.5% of PM10 mass concentration, whereas elements contribution to PM10 was estimated to be 17% of PM10. The statistical analysis of OC vs. EC and OC vs. WSOC of PM10 reveals their common sources (biomass burning and/or fossil fuel combustion) during all the seasons. Enrichment factors (EFs) of the elements and the relationship of Al with other crustal metals (Fe, Ca, Mg and Ti) of PM10 indicates the abundance of mineral dust over Delhi. Principal component analysis (PCA) extracted the five major sources [industrial emission (IE), biomass burning + fossil fuel combustion (BB + FFC), soil dust, vehicular emissions (VE) and sodium and magnesium salts (SMS)] of PM10 in Delhi, India. Back trajectory and cluster analysis of airmass parcel indicate that the pollutants approaching to Delhi are mainly from Pakistan, IGP region, Arabian Sea and Bay of Bengal. [ABSTRACT FROM AUTHOR]

Remote sensing of greenhouse gases (GHGs) in cities, where high GHG emissions are typically associated with heavy aerosol loading, is challenging due to retrieval uncertainties caused by the imperfect characterization of scattering by aerosols. We investigate this problem by developing GFIT3, a full physics algorithm to retrieve GHGs (CO2 and CH4) by accounting for aerosol scattering effects in polluted urban atmospheres. In particular, the algorithm includes coarse- (including sea salt and dust) and fine- (including organic carbon, black carbon, and sulfate) mode aerosols in the radiative transfer model. The performance of GFIT3 is assessed using high-spectral-resolution observations over the Los Angeles (LA) megacity made by the California Laboratory for Atmospheric Remote Sensing Fourier transform spectrometer (CLARS-FTS). CLARS-FTS is located on Mt. Wilson, California, at 1.67 km a.s.l. overlooking the LA Basin, and it makes observations of reflected sunlight in the near-infrared spectral range. The first set of evaluations are performed by conducting retrieval experiments using synthetic spectra. We find that errors in the retrievals of column-averaged dry air mole fractions of CO2 (XCO2) and CH4 (XCH4) due to uncertainties in the aerosol optical properties and atmospheric a priori profiles are less than 1 % on average. This indicates that atmospheric scattering does not induce a large bias in the retrievals when the aerosols are properly characterized. The methodology is then further evaluated by comparing GHG retrievals using GFIT3 with those obtained from the CLARS-GFIT algorithm (used for currently operational CLARS retrievals) that does not account for aerosol scattering. We find a significant correlation between retrieval bias and aerosol optical depth (AOD). A comparison of GFIT3 AOD retrievals with collocated ground-based observations from AErosol RObotic NETwork (AERONET) shows that the developed algorithm produces very accurate results, with biases in AOD estimates of about 0.02. Finally, we assess the uncertainty in the widely used tracer–tracer ratio method to obtain CH4 emissions based on CO2 emissions and find that using the CH4/CO2 ratio effectively cancels out biases due to aerosol scattering. Overall, this study of applying GFIT3 to CLARS-FTS observations improves our understanding of the impact of aerosol scattering on the remote sensing of GHGs in polluted urban atmospheric environments. GHG retrievals from CLARS-FTS are potentially complementary to existing ground-based and spaceborne observations to monitor anthropogenic GHG fluxes in megacities. [ABSTRACT FROM AUTHOR]

The study represents the seasonal characteristics (carbonaceous aerosols and elements) and the contribution of prominent sources of PM2.5 and PM10 in the high altitude of the eastern Himalaya (Darjeeling) during August 2018–July 2019. Carbonaceous aerosols [organic carbon (OC), elemental carbon (EC), and water soluble organic carbon (WSOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Cr, Ni, Mo, Cl, P, S, K, Zr, Pb, Na, Mg, Ca, and B) in PM2.5 and PM10 were analyzed to estimate their possible sources. The annual concentrations of PM2.5 and PM10 were computed as 37±12 μg m−3 and 58±18 μg m−3, respectively. In the present case, total carbonaceous species in PM2.5 and PM10 were accounted for 20.6% of PM2.5 and 18.6% of PM10, respectively, whereas trace elements in PM2.5 and PM10 were estimated to be 15% of PM2.5 and 12% of PM10, respectively. Monthly and seasonal variations in mass concentrations of carbonaceous aerosols and elements in PM2.5 and PM10 were also observed during the observational period. In PM2.5, the annual concentrations of POC and SOC were 2.35 ± 1.06 μg m−3 (66% of OC) and 1.19±0.57 μg m−3 (34% of OC), respectively, whereas annual average POC and SOC concentrations in PM10 were 3.18 ± 1.13 μg m−3 (63% of OC) and 2.05±0.98 μg m−3 (37% of OC), respectively. The seasonal contribution of POC and SOC were ranging from 55 to 77% and 33 to 45% of OC in PM2.5, respectively, whereas in PM10, the seasonal contributions of POC and SOC were ranging from 51 to 73% and 37 to 49% of OC, respectively. The positive relationship between OC & EC and OC & WSOC of PM2.5 and PM10 during all the seasons (except monsoon in case of PM10) indicates their common sources. The enrichment factors (EFs) and significant positive correlation of Al with othe crustal elements (Fe, Ca, Mg, and Ti) of fine and coarse mode aerosols indicate the influence of mineral dust at Darjeeling. Principal component analysis (PCA) resolved the four common sources (biomass burning + fossil fuel combustion (BB + FFC), crustal/soil dust, vehicular emissions (VE), and industrial emissions (IE)) of PM2.5 and PM10 in Darjeeling. [ABSTRACT FROM AUTHOR]

Using 14 years (2007–2020) of data from passive (MODIS/Aqua) and active (CALIOP/CALIPSO) satellite measurements over China, we investigate (1) the temporal and spatial variation of aerosol properties over the Beijing–Tianjin–Hebei (BTH) region, the Yangtze River Delta (YRD), and the Pearl River Delta (PRD) and (2) the vertical distribution of aerosol types and extinction coefficients for different aerosol optical depth (AOD) and meteorological conditions. The results show the different spatial patterns and seasonal variations of the AOD over the three regions. Annual time series reveal the occurrence of AOD maxima in 2011 over the YRD and in 2012 over the BTH and PRD; thereafter the AOD decreases steadily. Using the CALIOP vertical feature mask, the relative frequency of occurrence (rFO) of each aerosol type in the atmospheric column is analyzed: rFOs of dust and polluted dust decrease from north to south; rFOs of clean ocean, polluted continental, clean continental and elevated smoke aerosol increase from north to south. In the vertical, the peak frequency of occurrence (FO) for each aerosol type depends on region and season and varies with AOD and meteorological conditions. In general, three distinct altitude ranges are observed with the peak FO at the surface (clean continental and clean marine aerosol), at ∼1 km (polluted dust and polluted continental aerosol) and at ∼3 km (elevated smoke aerosol), whereas dust aerosol may occur over the whole altitude range considered in this study (from the surface up to 8 km). The designation of the aerosol type in different height ranges may to some extent reflect the CALIOP aerosol type classification approach. Air mass trajectories indicate the different source regions for the three study areas and for the three different altitude ranges over each area. In this study nighttime CALIOP profiles are used. The comparison with daytime profiles shows substantial differences in the FO profiles with altitude, which suggest effects of boundary layer dynamics and aerosol transport on the vertical distribution of aerosol types, although differences due to day–night CALIOP performance cannot be ruled out. [ABSTRACT FROM AUTHOR]

• The heavy haze episodes formation in autumn was related with the increase of secondary organic aerosols and NH 4. • The contribution of POC and NH 4 + were significant during the evolution of pollution periods in wintertime. • The local and short-distance air mass transportation have significant impact. To study the pollution features and underlying mechanism of PM 2.5 in Luoyang, a typical developing urban site in the central plain of China, 303 PM 2.5 samples were collected from April 16 to December 29, 2015 to analyze the elements, water soluble inorganic ions, organic carbon and elemental carbon. The annual mean concentration of PM 2.5 was 142.3 μg/m3, and 75% of the daily PM 2.5 concentrations exceeded the 75 μg/m3. The secondary inorganic ions, organic matter and mineral dust were the most abundant species, accounting for 39.6%, 19.2% and 9.3% of the total mass concentration, respectively. But the major chemical components showed clear seasonal dependence. SO 4 2− was most abundant specie in spring and summer, which related to intensive photochemical reaction under high O 3 concentration. In contrast, the secondary organic carbon and ammonium while primary organic carbon and ammonium significantly contributed to haze formation in autumn and winter, respectively. This indicated that the collaboration effect of secondary inorganic aerosols and carbonaceous matters result in heavy haze in autumn and winter. Six main sources were identified by positive matrix factorization model: industrial emission, combustion sources, traffic emission, mineral dust, oil combustion and secondary sulfate, with the annual contribution of 24%, 20%, 24%, 4%, 5% and 23%, respectively. The potential source contribution function analysis pointed that the contribution of the local and short-range regional transportation had significant impact. This result highlighted that local primary carbonaceous and precursor of secondary carbonaceous mitigation would be key to reduce PM 2.5 and O 3 during heavy haze episodes in winter and autumn. [Display omitted] [ABSTRACT FROM AUTHOR]

Black carbon (BC), brown carbon (BrC), and soil dust are the most important radiation-absorbing aerosols (RAAs). When RAAs are deposited on the snowpack, they lower the snow albedo, causing an increase in the solar radiation absorption. The climatic impact associated with the snow darkening induced by RAAs is highly uncertain. The Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) attributes low and medium confidence to radiative forcing (RF) from BrC and dust in snow, respectively. Therefore, the contribution of anthropogenic sources and carbonaceous aerosols to RAA RF in snow is not clear. Moreover, the snow albedo perturbation induced by a single RAA species depends on the presence of other light-absorbing impurities contained in the snowpack. In this work, we calculated the present-day RF of RAAs in snow starting from the deposition fields from a 5-year simulation with the GEOS-Chem global chemistry and transport model. RF was estimated taking into account the presence of BC, BrC, and mineral soil dust in snow, simultaneously. Modeled BC and black carbon equivalent (BCE) mixing ratios in snow and the fraction of light absorption due to non-BC compounds (fnon-BC) were compared with worldwide observations. We showed that BC, BCE, and fnon-BC , obtained from deposition and precipitation fluxes, reproduce the regional variability and order of magnitude of the observations. Global-average all-sky total RAA-, BC-, BrC-, and dust-snow RF were 0.068, 0.033, 0.0066, and 0.012 W m -2 , respectively. At a global scale, non-BC compounds accounted for 40 % of RAA-snow RF, while anthropogenic RAAs contributed to the forcing for 56 %. With regard to non-BC compounds, the largest impact of BrC has been found during summer in the Arctic (+ 0.13 W m -2). In the middle latitudes of Asia, the forcing from dust in spring accounted for 50 % (+ 0.24 W m -2) of the total RAA RF. Uncertainties in absorbing optical properties, RAA mixing ratio in snow, snow grain dimension, and snow cover fraction resulted in an overall uncertainty of - 50 %/ + 61 %, - 57 %/ + 183 %, - 63 %/ + 112 %, and - 49 %/ + 77 % in BC-, BrC-, dust-, and total RAA-snow RF, respectively. Uncertainty upper bounds of BrC and dust were about 2 and 3 times larger than the upper bounds associated with BC. Higher BrC and dust uncertainties were mainly due to the presence of multiple absorbing impurities in the snow. Our results highlight that an improvement of the representation of RAAs in snow is desirable, given the potential high efficacy of this forcing. [ABSTRACT FROM AUTHOR]

To investigate the particle sources before, during, and after the 2022 Beijing Winter Olympic and Paralympic (WOP) in Beijing, ambient particles were passively collected from January to March 2022. The physicochemical properties including morphology, size, shape parameters, and elemental compositions were analyzed by the IntelliSEM EPAS (an advanced computer-controlled scanning electron microscopy [CCSEM] system). Using the user-defined classification rules, 37,174 individual particles were automatically classified into 27 major groups and further attributed to seven major sources based on the source-associated characteristics, including mineral dust, secondary aerosol, combustion/industry, carbonaceous particles, salt-related particles, biological particles, and fiber particles. Our results showed that mineral dust (66.5%), combustion/industry (12.6%), and secondary aerosol (6.3%) were the three major sources in a wide size range of 0.2–42.8 μm. During the Winter Olympic Games period, low emission of anthropogenic particles and favorable meteorological conditions contributed to significantly improved air quality. During the Winter Paralympic Games period, more particles sourced from the dust storm, secondary formed particles, and the adverse meteorological conditions resulted in relatively worse air quality. The secondary aerosol all decreased during the competition period, while increased during the non-competition period. Sulfate-related particles had explosive growth and further aggravate the pollution degree during the non-competition period, especially under adverse meteorological conditions. These results provide microscopic evidence revealing variations of physicochemical properties and sources in response to the control measures and meteorological conditions. [Display omitted] • Mineral dust, combustion/industry, and secondary aerosol were the top three sources of aerosol particle (0.2–42.8 μm). • Notable decreases in anthropogenic particles were observed during competition period by IntelliSEM EPAS. • Dramatic rise in secondarily formed particles mainly exacerbated pollution levels during non-competition period. • Winter Olympics had better air quality primarily benefited from significant emission reductions and favorable weathers. • Winter Paralympics faced deteriorated air quality due to dust storm and haze event under adverse weather. [ABSTRACT FROM AUTHOR]

In this study, we investigated the seasonal variations, chemical composition, sources, and oxidative potential of ambient PM 2.5 (particles with a diameter of less than 2.5 μm) in Kuwait City. The sampling campaign was conducted within the premises of Kuwait Institute for Scientific Research from June 2022 to May 2023, covering different seasons throughout the year. The personal cascade impactor sampler (PCIS) operated at flow rate of 9 L/min was employed to collect weekly PM 2.5 samples on PTFE and quarts filters. These collected samples were analyzed for carbonaceous species (i.e., elemental and organic carbon), metals and transition elements, inorganic ions, and DTT (dithiothreitol) redox activity. Furthermore, principal component analysis (PCA) and multi-linear regression (MLR) were used to identify the predominant emission sources and their percentage contribution to the redox activity of PM 2.5 in Kuwait. The results of this study highlighted that the annual-averaged ambient PM 2.5 mass concentrations in Kuwait (59.9 μg/m3) substantially exceeded the World Health Organization (WHO) guideline of 10 μg/m3. Additionally, the summer season displayed the highest PM 2.5 mass concentration (75.2 μg/m3) compared to other seasons, primarily due to frequent dust events exacerbated by high-speed winds. The PCA identified four primary PM 2.5 sources: mineral dust, fossil fuel combustion, road traffic, and secondary aerosols. The mineral dust was found to be the predominant source, contributing 36.1% to the PM 2.5 mass, followed by fossil fuel combustion and traffic emissions with contributions of 23.7% and 20.3%, respectively. The findings of MLR revealed that road traffic was the most significant contributor to PM 2.5 oxidative potential, accounting for 47% of the total DTT activity. In conclusion, this comprehensive investigation provides essential insights into the sources and health implications of PM 2.5 in Kuwait, underscoring the critical need for effective air quality management strategies to mitigate the impacts of particulate pollution in the region. [Display omitted] • PCA and MLR were used to identify the contribution of PM 2.5 sources to DTT activity. • Annual average PM 2.5 level in Kuwait was six times higher than WHO recommendation. • PM 2.5 sources were mineral dust, fuel combustion, traffic, and secondary aerosols. • Road traffic was the predominant contributor (47%) to PM 2.5 oxidative potential. [ABSTRACT FROM AUTHOR]

The POLIPHON (Polarization Lidar Photometer Networking) method is a powerful pathway to retrieve the height profiles of dust-related particle mass and ice-nucleating particles (INP) concentrations. The conversion factors fitted from the sun photometer observation data are the major part of the POLIPHON computations, which can convert the polarizationlidar- derived dust extinction coefficients into the dust-related particle mass and INP concentrations. For a central China megacity Wuhan (30.5°N, 114.4°E), located at the downstream area several thousands of kilometers far away from the source regions of Asian dust, dust particles always mix with other aerosols from local emission. Therefore, very few dust case data sets can be available when using the column-integrated Ångström exponent (for 440-870 nm) <0.3 and aerosol optical depth (at 532 nm) >0.1 recorded by sun photometer as the filtering criteria. Instead, we present another dust-case data-set screening scheme that applies the simultaneous polarization lidar observation to verify the occurrence of dust. Based on the 33 dust-intrusion days identified during 2011-2013, the extinction-to-volume (푐푣,푑) and extinction-to-large particle (with radius >250 nm) number concentration (푐250,푑) conversion factors are determined to be 0.52 × 10-12 Mm m³m-3 and 0.11 Mm cm-3, respectively. They are both smaller than those observed at Lanzhou SACOL (36.0°N, 104.1°E), a site closer to the Gobi Desert, due to the partial dust sedimentation during transport. The conversion factors are applied in a dust event in Wuhan to reveal the typical dust-related INP concentration over East Asia city. The proposed dust-case data-set screening scheme may potentially be extended to the other polluted city sites more influenced by mixed dust. [ABSTRACT FROM AUTHOR]

Atmospheric extinction is impacted by the chemical composition of particles. To better understand the chemical composition of PM 2.5 (particles with diameters of less than 2.5 μm) and its relationship with extinction, one-month sampling campaigns were carried out in four different seasons from 2013 to 2014 in Jinan, China. The seasonal average concentrations of PM 2.5 were 120.9 (autumn), 156.6 (winter), 102.5 (spring), and 111.8 μg/m3 (summer). The reconstructed PM 2.5 chemical composition showed that sulfate, nitrate, chlorine salt, organic matter (OM), mineral dust, elemental carbon (EC) and others accounted for 25%, 14%, 2%, 24%, 22%, 3% and 10%, respectively. The relationship between the chemical composition of PM 2.5 and visibility was reconstructed by the IMPROVE method, and ammonium sulfate, ammonium nitrate, OM and EC dominated the visibility. Seven main sources were resolved for PM 2.5 , including secondary particles, coal combustion, biomass burning, industry, motor vehicle exhaust, soil dust and cooking, which accounted for 37%, 21%, 13%, 13%, 12%, 3% and 1%, respectively. The contributions of different sources to visibility were similar to those to PM 2.5. With increasing severity of air pollution, the contributions of secondary particles and coal combustion increased, while the contribution of motor vehicle exhaust decreased. The results showed that coal combustion and biomass burning were still the main sources of air pollution in Jinan. Image, graphical abstract [ABSTRACT FROM AUTHOR]