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Atmospheric ammonia (NH3) is a key transboundary air pollutant that contributes to the impacts of nitrogen and acidity on terrestrial ecosystems. Ammonia also contributes to the atmospheric aerosol that affects air quality. Emission inventories indicate that NH3 was predominantly emitted by agriculture over the 19th and 20th centuries but, up to now, these estimates have not been compared to long-term observations. To document past atmospheric NH3 pollution in south-eastern Europe, ammonium (NH 4+) was analysed along an ice core extracted from Mount Elbrus in the Caucasus, Russia. The NH 4+ ice-core record indicates a 3.5-fold increase in concentrations between 1750 and 1990 CE. Remaining moderate prior to 1950 CE, the increase then accelerated to reach a maximum in 1989 CE. Comparison between ice-core trends and estimated past emissions using state-of-the-art atmospheric transport modelling of submicron-scale aerosols (FLEXPART (FLEXible PARTicle dispersion) model) indicates good agreement with the course of estimated NH3 emissions from south-eastern Europe since ∼ 1750 CE, with the main contributions from south European Russia, Türkiye, Georgia, and Ukraine. Examination of ice deposited prior to 1850 CE, when agricultural activities remained limited, suggests an NH 4+ ice concentration related to natural soil emissions representing ∼ 20 % of the 1980–2009 CE NH 4+ level, a level mainly related to current agricultural emissions that almost completely outweigh biogenic emissions from natural soil. These findings on historical NH3 emission trends represent a significant contribution to the understanding of ammonia emissions in Europe over the last 250 years. [ABSTRACT FROM AUTHOR]

A rare phenomenon—the long-range atmospheric transport of dust from the arid and semiarid territories of the Caspian Sea region through the center of the European part of Russia to its Arctic areas—was recorded in December 2023 during a field study of the physicochemical characteristics of airborne particles in Moscow and the snow composition in Arkhangelsk oblast. The analysis of the trajectories of the air mass transport, dynamics of spatial and temporal variability of the mass concentration of PM2.5 and PM10 matter in Moscow oblast, and numerical estimates and spatial distributions of near-surface concentrations and optical characteristics of airborne particles in the European part of Russia (according to the MERRA-2 reanalysis estimates) confirmed an increase in aerosol air pollution in the territories from the Caspian Sea to Arkhangelsk oblast. The snow sample taken in the area of Pinega Nature Reserve, Arkhangelsk oblast, in the spring of 2024, in the snow cover at a height of 18–20 cm (with a total snow thickness of 65 cm), was found to contain a yellowish layer of snow that fell in December 2023. The preliminary studies of the sample from this snow showed the presence of a large amount of organic suspended matter and plant residue, which in winter indicates transport of atmospheric aerosol from the southern regions of Russia. [ABSTRACT FROM AUTHOR]

A linear non‐diffusive algorithm for advective transport is developed that greatly improves the detail at which aerosols and clouds can be represented in atmospheric models. Linear advection schemes preserve tracer correlations but the most basic linear scheme is rarely used by atmospheric modelers on account of its excessive numerical diffusion. Higher‐order schemes are in widespread use, but these present new problems as nonlinear adjustments are required to avoid occurrences of negative concentrations, spurious oscillations, and other non‐physical effects. Generally successful at reducing numerical diffusion during the advection of individual tracers, for example, particle number or mass, the higher‐order schemes fail to preserve even the simplest of correlations between interrelated tracers. As a result, important attributes of aerosol and cloud populations including radial moments of particle size distributions, molecular precursors related through chemical equilibria, aerosol mixing state, and distribution of cloud phase are poorly represented. We introduce a new transport scheme, minVAR, that is both non‐diffusive and preservative of tracer correlations, thereby combining the best features of the basic and higher‐order schemes while enabling new features such as the tracking of sub‐grid information at arbitrarily fine scales with high computational efficiency. Plain Language Summary: A long‐standing challenge for the representation of aerosols and clouds in atmospheric models is to properly transport particles in space using higher‐order advection schemes. These schemes have less numerical diffusion than the simple basic scheme, but cannot maintain the physical relationship between particle number and mass that needs to be simulated correctly for better understanding of aerosol‐cloud‐turbulence interactions either in a laboratory‐scale cloud chamber or at larger atmospheric scales. The present advection scheme (minVAR, short for minimum variance) introduces a diffusion limiter, under the idea that achieving minimal spatial variance on an Eulerian grid implies maximal resolution and—it turns out ‐ complete elimination of numerical diffusion. By preserving tracer correlations and eliminating numerical diffusion, minVAR includes the best features of the simple basic and higher‐order schemes. This innovation resolves the two‐moment limitation, a necessary first step toward the high‐fidelity, multi‐moment, multi‐scale representation of aerosols and clouds in atmospheric models. Moments, because they are so strongly and nonlinearly correlated, provide an excellent example of correlation failure and serve to focus the present study. That said, there is no reason to suggest that the methods developed here would be inapplicable to other correlated tracer sets. Key Points: A diffusion limiter—minVAR—was added to the linear basic advection scheme and found to eliminate numerical diffusion completelyThe minimum variance property of minVAR makes the new method optimal for advection of independent tracers as well as correlated onesminVAR establishes a unique one‐to‐one correspondence between points along a Lagrangian trajectory and their mapping to the Eulerian grid [ABSTRACT FROM AUTHOR]

The physicochemical properties and origins of atmospheric aerosols in the Tibetan Plateau (TP) region are a research topic of great interest, but an in‐depth understanding of this topic is challenging, partially due to a lack of intensive in situ observations. Thus, a field campaign was conducted over Yadong, a remote area on the south slope of the TP from June 11 to 31 August 2021. The aerosol loading was low, with a black carbon mass concentration of 147.4 ± 98.4 ng·m−3. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and increased from 450 to 700 nm wavelength. Organic matter (OM) accounting for 69.6% of the total aerosol mass and relatively high secondary organic carbon ratios, highlighting the importance of secondary formation. An interesting phenomenon observed was that the evolution of aerosols was mainly characterized by diurnal variation, which could not be explained by large‐scale atmospheric processes such as Indian summer monsoon. Instead, it was found that regional mountain‐valley winds between the Himalayas and South Asia transported polluted air masses toward the TP, especially in the afternoon when regional valley wind are expected to be the strongest and the boundary layer in South Asia is deepest. Additionally, daytime local valley wind further elevated these aerosols to higher altitudes on the TP. This paper provides insights into the transport mechanisms of aerosols from South Asia to the TP. These findings are of great importance since aerosols exhibit significant diurnal variations in the TP region. Plain Language Summary: Previous studies focused on the analysis of the physical or chemical properties of aerosols on the Tibetan Plateau, but this study provides a comprehensive examination of both. The findings reveal that aerosols on the southern slope of the Tibetan Plateau exhibit strong absorption efficiency. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm), which may be attributed to aerosol secondary generation and coating. Finally, the mechanism of pollutant transport from South Asia to the Tibetan Plateau was analyzed relies on site observations, satellite, and reanalysis data to highlight the link between diurnal variations of pollutants and transport mechanism. The specific transport mechanism be understood uniformly across different scales, including Indian summer monsoon, regional mountain‐valley winds between the Himalayas and South Asia, and local mountain‐valley winds circulation. Key Points: Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and secondary organic matter was the major aerosol componentThe evolution of aerosols was mainly characterized by diurnal variation that was related to transport mechanism over YadongThe Himalayas‐South Asia regional mountain‐valley winds combined with local mountain‐valley winds transport aerosols to the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Atmospheric new particle formation (NPF) and associated production of secondary particulate matter dominate aerosol particle number concentrations and submicron particle mass loadings in many environments globally. Our recent investigations show that atmospheric NPF produces a significant amount of particles on days when no clear NPF event has been observed/identified. Furthermore, it has been observed in different environments all around the world that growth rates of nucleation mode particles vary little, usually much less than the measured concentrations of condensable vapors. It has also been observed that the local clustering, which in many cases acts as a starting point of regional new particle formation (NPF), can be described with the formation of intermediate ions at the smallest sizes. These observations, together with a recently developed ranking method, lead us to propose a paradigm shift in atmospheric NPF investigations. In this opinion paper, we will summarize the traditional approach of describing atmospheric NPF and describe an alternative method, covering both particle formation and initial growth. The opportunities and remaining challenges offered by the new approach are discussed. [ABSTRACT FROM AUTHOR]

Water is a key component of atmospheric aerosol, affecting many aerosol processes including gas-to-particle partitioning of semi-volatile compounds. Water related to secondary organic aerosol (SOAW) is often neglected in atmospheric chemical transport models and is not considered in gas-to-particle partitioning calculations for inorganic species. We use a new inorganic aerosol thermodynamics model, ISORROPIA-lite, which considers the effects of SOAW, to perform chemical transport model simulations for 1 year over the continental United States to quantify its effects on aerosol mass concentration and composition. SOAW can increase average fine aerosol water levels by up to a factor of 2 when secondary organic aerosol (SOA) is a major PM 1 component. This is often the case in the south-eastern US, where SOA concentrations are higher. Although the annual average impact of this added water on total dry PM 1 concentrations due to increased partitioning of nitrate and ammonium is small (up to 0.1 µ g m -3), total dry PM 1 increases of up to 2 µ g m -3 (with nitrate levels increases of up to 200 %) can occur when RH levels and PM 1 concentrations are high. [ABSTRACT FROM AUTHOR]

A global aerosol–climate model is applied to quantify the impact of the transport sectors (land transport, shipping, and aviation) on aerosol and climate. Global simulations are performed for the present day (2015), based on the emission inventory of the Climate Model Intercomparison Project Phase 6 (CMIP6), and for near-term (2030) and mid-term (2050) future projections, under the Shared Socioeconomic Pathways (SSPs). The results for the present day show that land transport emissions have a large impact on near-surface concentrations of black carbon and aerosol nitrate over the most populated areas of the globe, but with contrasting patterns in terms of relative contributions between developed and developing countries. In spite of the recently introduced regulations to limit the fuel sulfur content in the shipping sector, shipping emissions are still responsible for a considerable impact on aerosol sulfate near-surface concentrations, about 0.5 to 1 µ g m -3 in the most travelled regions, with significant effects on continental air pollution and in the northern polar regions as well. Aviation impacts on aerosol mass are found to be quite small, of the order of a few nanograms per cubic metre, while this sector considerably affects particle number concentrations, contributing up to 20 %–30 % of the upper-tropospheric particle number concentration at the northern mid-latitudes. The transport-induced impacts on aerosol mass and number concentrations result in a present-day radiative forcing of -164 , -145 , and -64 mW m -2 for land transport, shipping, and aviation, respectively, with a dominating contribution by aerosol–cloud interactions. These forcings represent a marked offset to the CO 2 warming from the transport sectors and are therefore very relevant for climate policy. The projections under the SSPs show that the impact of the transport sectors on aerosol and climate are generally consistent with the narratives underlying these scenarios: the lowest impacts of transport on both aerosol and climate are simulated under SSP1, especially for the land transport sector, while SSP3 is generally characterized by the largest effects. Notable exceptions to this picture, however, exist, as the emissions of other anthropogenic sectors also contribute to the overall aerosol concentrations and thus modulate the relevance of the transport sectors in the different scenarios, not always consistently with their underlying storyline. On a qualitative level, the results for the present day mostly confirm the findings of our previous assessment for the year 2000, which used a predecessor version of the same model and the CMIP5 emission data. Some important quantitative differences are found, which can mostly be ascribed to the improved representation of aerosol background concentrations in the present study. [ABSTRACT FROM AUTHOR]

The present study focused on the temporal variability, meteorological influences, potential sources, and long-range transport of atmospheric aerosols over two contrasting environments during 2011–2013. We have chosen Agartala (AGR) city in Northeast India as one of our sites representing the rural-continental environment and Patiala (PTA) as an urban site in Northwest India. The seasonal averaged equivalent black carbon (eBC) concentration in AGR ranges from 1.55 to 38.11 µg/m3 with an average value of 9.87 ± 8.17 µg/m3, whereas, at an urban location, PTA value ranges from 1.30 to 15.57 µg/m3 with an average value of 7.83 ± 3.51 µg/m3. The annual average eBC concentration over AGR was observed to be ~ 3 times higher than PTA. Two diurnal peaks (morning and evening) in eBC have been observed at both sites but were observed to be more prominent at AGR than at PTA. Spectral aerosol optical depth (AOD) has been observed to be in the range from 0.33 ± 0.09 (post-monsoon) to 0.85 ± 0.22 (winter) at AGR and 0.47 ± 0.04 (pre-monsoon) to 0.74 ± 0.09 (post-monsoon) at PTA. The concentration of eBC and its diurnal and seasonal variation indicates the primary sources of eBC as local sources, synoptic meteorology, planetary boundary layer (PBL) dynamics, and distant transportation of aerosols. The wintertime higher values of eBC at AGR than at PTA are linked with the transportation of eBC from the Indo-Gangetic Plain (IGP). Furthermore, it is evident that eBC aerosols are transported from local and regional sources, which is supported by concentration-weighted trajectory (CWT) analysis results. [ABSTRACT FROM AUTHOR]

Long‐range transport and vertical distribution of aerosols are important factors for assessing the uncertainty in aerosol radiative forcing. This paper reveals the vertical distribution and trends of aerosol optical properties in China using 15 years of Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The Hybrid Single‐Particle Lagrangian integrated trajectory model was used to analyze the transport and trends of aerosols in the layer with the highest occurrence frequencies of dust, polluted dust, polluted continental and elevated smoke aerosols. The results indicated that (a) there were significant regional and seasonal differences in the vertical distribution of aerosols. The aerosol optical depth (AOD) trend in a given region depends on the changes in the aerosol type with the highest frequency and the layer corresponding to the largest AOD in the vertical profile. The frequency of polluted dust aerosols was the highest in Beijing‐Tianjin‐Hebei (BTH) and Central China. The considerable decrease in the 0–2 km AOD led to a significant trend of the column AOD. (b) The changes of AOD and main aerosol types in a region are also affected by the changes of aerosol sources and long‐range transport pathways. In the BTH, dust aerosols originated from the Mongolian Plateau, accounting for 57.88% of the total trajectories. The Pearl River Delta was dominated by elevated smoke aerosols, with trajectories mainly originating from the Myanmar and Vietnam, accounting for 27.38% and 29.59%, respectively. The trend of 15‐year backward trajectories of dust aerosols on the Tibetan Plateau indicated that the trajectory from India is increasing. Plain Language Summary: Aerosols are one of the main factors affecting global climate change, influencing global radiation through direct and indirect effects. Long‐range transport aerosols and their vertical distribution are important factors for assessing the uncertainty in aerosol radiative forcing. At present, there is limited research on the vertical distribution and transport pathways of different types of aerosols in multiple regions over China. Considering that aerosols in different regions of China exhibit large vertical distribution and transport differences, we revealed the vertical distribution and trends of aerosol optical properties in China using 15 years of Cloud‐Aerosol Lidar with Orthogonal Polarization data. The Hybrid Single‐Particle Lagrangian Integrated Trajectory model was used to analyze the transport and trends of different aerosols. We found significant regional and seasonal differences in the vertical distributions of aerosols. The changes in the aerosol optical depth and main aerosol types in a given region were also significantly affected by the changes in aerosol transport sources and transport pathways. This study provides comprehensive insight into the vertical distribution and transport characteristics of different types of atmospheric aerosols in the Chinese region over the last 15 years, which is very important to further evaluation of the impact of different aerosol types on the radiative effects and the environment. Key Points: The vertical distribution of aerosol optical properties exhibits notable seasonal and regional differences using 15 years of Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) dataThe trend of total aerosol optical depth (AOD) mainly depends on the joint changes of the highest frequency aerosol and the maximum AOD layer in a vertical profileThe changes of AOD and main aerosol types in a region are also affected by the changes of aerosol transport sources and transport pathways [ABSTRACT FROM AUTHOR]

Proteinaceous matter (PrM) is a substantial constituent in bioaerosols. However, the sources and atmospheric processes of PrM remain large uncertainties. The characterizations, sources, and potential atmospheric processes of free amino acids (FAAs) and combined amino acids (CAAs) were investigated via a set of 1‐year fine particle (PM2.5) samples collected in suburban Guiyang (a hilly basin area in Southwest China). The annual average concentrations of FAAs and CAAs were 156.31 ± 41.52 and 315.36 ± 147.66 ng m−3, respectively. The dominant FAA and CAA species were proline, which was different from previous observations with glycine as a major species. The results indicated that the sources or atmospheric processes of aerosol PrM at this study site were different from previous observations in the urban and suburban areas. The analysis of AA‐nitrogen isotope compositions and air mass back trajectories suggested that the abundances of aerosol FAAs and CAAs were highly controlled by primary sources (particularly plants) with less impact from long‐range transport. Furthermore, the contributions of PrM degradation by ozone‐ and hydroxyl radical‐related processes to total FAAs were found to be minor. The overall results suggested that the long‐range transport and atmospheric degradation of PrM were insignificant factors affecting aerosol PrM abundance in this suburban area with the weak atmospheric oxidation capacity, high cloud cover rate, and frequent precipitation. Thus, the findings improve our understanding of the sources and atmospheric processes of aerosol PrM. Plain Language Summary: Aerosol proteinaceous matter (PrM) consists of free amino acids (FAAs) and combined amino acids (CAAs). It is well documented that FAAs and CAAs have a large variety of natural sources. Moreover, the atmospheric degradation of CAAs has been regarded as a new potential source of aerosol FAAs. However, the relative contribution of primary and secondary sources to FAAs remains poorly understood. Based on a 1‐year investigation of PrM in PM2.5 collected in suburban Guiyang (a hilly basin area in Southwest China), we found that proline was the dominant species in both FAAs and CAAs. This result was different from previous observations with glycine as a major species. Further, our analysis showed that aerosol PrM in this hilly basin area was mainly derived from local primary sources (particularly plants) with less influence from long‐range transport of PrM. Moreover, the contribution of oxidative degradation of PrM to total FAAs was found to be minor. In general, the long‐range transport and atmospheric degradation of PrM have an insignificant contribution to aerosol PrM abundance in this hilly basin area. Our findings provide new insights into the sources and atmospheric transformation of aerosol PrM. Key Points: Proline is the dominant species in both free amino acids and combined amino acidsAerosol Proteinaceous matter (PrM) was largely originated from local primary sources with less impact from long‐range transportThe oxidative degradation of aerosol PrM was insignificant in suburban Guiyang [ABSTRACT FROM AUTHOR]

To investigate the spatial changes in origins and impact of long‐range transported air masses on organic aerosols (OA) loading and composition over Northeast Asia, fine aerosols (PM2.5) were collected at three sites: Tianjin (TJ), North China and in Padori (PD), and Daejeon (DJ), South Korea, during winter 2019. We studied molecular distributions and compound‐specific stable carbon isotopic composition (δ13C) of dicarboxylic acids, oxocarboxylic acids and α‐dicarbonyls, and carbonaceous and inorganic ionic components in PM2.5. Concentrations of organic carbon was drastically enhanced in haze period compared to that in clean period, but elemental carbon was almost comparable between the two periods. Concentrations of total diacids, oxoacids, and α‐dicarbonyls were higher at TJ followed by DJ and PD during haze period and at DJ followed by TJ and PD during clean period. On average, oxalic acid (C2) was the most abundant among measured species at all three sites, followed by methyl glyoxal (MeGly) and glyoxylic acid (ωC2) at TJ and DJ, and succinic acid (C4) and ωC2 were almost equal and second most abundant followed by MeGly at PD. Based on the mass ratios and linear relations of selected species together with δ13C of diacids and related compounds, we found that contributions of OA from biomass burning/biogenic emissions and their aging were higher at TJ and PD, whereas at DJ, emissions from anthropogenic sources and in situ secondary formation were also important. Furthermore, this study implies that long‐range atmospheric transport of aerosols from source regions to downwind regions are substantial over Northeast Asia. Plain Language Summary: Fine atmospheric aerosols (PM2.5) collected at three sites: Tianjin (TJ), North China and in Padori (PD), and Daejeon (DJ), South Korea, during winter 2019 were studied for molecular distributions and compound‐specific carbon isotopic composition (δ13C) of dicarboxylic acids (diacids), oxocarboxylic acids (oxoacids), and α‐dicarbonyls as well as the carbonaceous and inorganic ionic components. The results obtained from this study suggested that the contributions of organic aerosols from biomass burning/biogenic emissions and their photochemical secondary formation and transformations (aging) are higher at TJ and PD, whereas at DJ, the emissions from anthropogenic sources and in situ secondary formation are also important. This study also implies that contributions of long‐range transported aerosols from source regions to downwind regions such as PD and DJ are substantial over Northeast Asia. Key Points: Diacids, oxoacids, and α‐diacarbonyls were characterized in fine aerosols (PM2.5) from Tianjin, China, and Padori and Daejeon, South KoreaBiomass burning/biogenic emissions and their aging are higher at Tianjin and Padori and anthropogenic emissions are also important at DaejeonLong‐range atmospheric transport of the air masses from source regions to downwind regions are substantial over the Notheast Asian region [ABSTRACT FROM AUTHOR]

The cosmogenic radionuclides 7Be and 10Be are useful aerosol tracers for atmospheric transport studies. Combining 7Be and 10Be measurements with an atmospheric transport model can not only improve our understanding of the radionuclide transport and deposition processes but also provide an evaluation of the transport process in the model. To simulate these aerosol tracers, it is critical to evaluate the influence of radionuclides production uncertainties on simulations. Here we use the GEOS-Chem chemical transport model driven by the MERRA-2 reanalysis to simulate 7Be and 10Be with different production scenarios: the default production rate in GEOS-Chem based on an empirical approach (denoted as LP67), and two production rates from the CRAC:Be (Cosmic Ray Atmospheric Cascade: Beryllium) model considering only geomagnetic cut-off rigidities for a geocentric axial dipole (denoted as P16) or realistic spatial geomagnetic cut-off rigidity variations due to non-dipole moments of the geomagnetic field (denoted as P16spa). The model results are comprehensively evaluated with a large number of measurements including surface air concentrations and deposition fluxes. The model with the P16spa production can reproduce the absolute values and temporal variability of 7Be and 10Be surface concentrations and deposition fluxes on annual and sub-annual scales, as well as the vertical profiles of air concentrations. Simulations with the LP67 production tend to overestimate the absolute values of 7Be and 10Be concentrations. The P16 simulations suggest less than 10% differences compared to P16spa but tend to produce a significant positive bias (>20%) in the 7Be deposition fluxes over East Asia. We find that the deposition fluxes are more sensitive to the production in the troposphere and downward transport from the stratosphere. Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. The model can also reasonably simulate the stratosphere-troposphere exchange process of 7Be and 10Be by producing stratospheric contribution and 10Be/7Be ratio values that agree with measurements. Finally, we illustrate the importance of including the time-varying solar modulation in the production calculation, which can significantly improve the agreement between model results and measurements, especially at mid- and high-latitudes. Reduced uncertainties in the production rates, as demonstrated in this study, improve the utility of 7Be and 10Be as aerosol tracers for evaluating and testing transport and scavenging processes in global models. [ABSTRACT FROM AUTHOR]

Size distributions of chemical species provide evidence for their sources and formation mechanisms. Size‐segregated aerosols with 12 sizes were collected over Northern Japan (Sapporo: 43.07°N and 141.35°E) during the spring (9 April–21 May) of 2001 and analyzed for water‐soluble organic and inorganic species. The dominances of SO42– and NH4+ in submicron (Da < 1.1 μm) and Na+ and Ca2+ in supermicron (Da > 1.1 μm) aerosols suggest substantial contributions from anthropogenic sources, sea‐salt and dust particles via long‐range atmospheric transport. Oxalic acid (C2) is the dominant organic species followed by malonic (C3) and succinic (C4) acid. A supermicron mode enrichment of C2 is heavily involved with the long‐range transport of dust particles, whereas submicron mode C2 was influenced by anthropogenic sources from the East Asian continent. The size distributions of shorter‐chain diacids (C3–C6), phthalic (Ph) and glyoxylic acid are consistent with those of C2, whereas azelaic acid (C9) is enriched in submicron and supermicron modes by the influences of continental and marine air masses. The mass concentration ratios of C3/C4 in submicron (1.5–2.3) and supermicron (1.2–1.8) mode demonstrated that water‐soluble organic aerosols in Sapporo were photochemically processed during long‐range transport. The Ph/C9 ratios show that the influence of anthropogenic sources on 9–28 April samples was pronounced in supermicron (2.5–2.9) than the submicron (1.1–1.2) particles, and vice‐versa on 6–21 May samples. These contrast distributions suggest that the continental air masses from East Asia and marine air masses from the surrounding ocean likely control the chemical composition of aerosols over Northern Japan. Plain Language Summary: Dicarboxylic acids make up a considerable portion of water‐soluble organic aerosols (OAs) in the atmosphere. We present the changes in the size distributions of water‐soluble secondary OAs during the ACE‐Asia campaign in the spring of 2001 in Northern Japan. The molecular distribution of dicarboxylic acids in size‐segregated aerosols with a predominance of oxalic acid (C2) followed by malonic acid implies that water‐soluble OAs over Northern Japan were photochemically aged. The substantial fraction of C2 on the supermicron mode aerosols is affected by the dust transported from the East Asian continent, suggesting its uptake or heterogeneous production on the surface of dust particles during long‐range transport to Northern Japan. Significant positive correlations of C2 and related compounds with Ca2+ in a supermicron mode further support a heterogeneous production of C2 in Ca2+‐enriched supermicron aerosols. The results suggest that the air masses from East Asia and the surrounding ocean mainly control the abundances of OAs over Northern Japan. The atmospheric abundance of secondary OAs could change due to the enhanced production of C2 in supermicron and submicron particles that can affect aerosol‐cloud interaction and radiative forcing of the most considerable fraction of water‐soluble secondary OAs. Key Points: The chemical composition of atmospheric aerosols over Northern Japan is controlled by continental and marine air massesOxalic acid size distribution is induced by the long‐range transport of dust particles and anthropogenic sourcesWater‐soluble organic aerosols over Northern Japan were photochemically processed during long‐range atmospheric transport [ABSTRACT FROM AUTHOR]

Organic aerosols (OA) are a main component of PM 2.5 (20–90%), which contains thousands of compounds. Thus, the formation processes and sources of OA remain poorly understood. In this study, the seasonal and diurnal variabilities of submicron PM chemical composition (both inorganic and organic aerosols) and OA sources were characterized by aerosol mass spectrometry (AMS) and an aethalometer at a rural background site in the Czech Republic (National Atmospheric Observatory Košetice – NAOK) from January to October 2019. The effects of meteorological conditions and local, regional, and long-range atmospheric transport influences in Central Europe were also studied. The overall average submicron PM concentration was 9.26 ± 5.88 μg m−3. Using positive matrix factorization (PMF) analysis, we identified four OA factors for summer and five for all other seasons. Three factors were associated with primary sources of OA (POA): hydrocarbon-like OA (HOA), biomass-burning OA (BBOA), and OA from coal burning (CCOA, absent in summer), the CCOA factor enabling a better description of the residential heating effect on the background station in Central Europe. Two remaining factors represented oxygenated OA (OOA) sources: less oxidized OOA (LO-OOA) and more oxidized OOA (MO-OOA).Higher pollution episodes of submicron PM and all OA sources were predominantly associated with continental air masses. The effect of dispersion conditions, as assessed by the ventilation index (VI) and not yet been studied at a rural background site, proved to be a critical factor. The extension of the number of primary factors to include CCOA in PMF analysis, together with the reflection of the influence of seasonality, air mass origin and changes in meteorology, especially dispersion conditions, has elucidated the origin and fate of OA in the atmosphere at this type of European background stations. [Display omitted] • OA sources varied by season, with the highest proportion of POA in winter. • OA were affected by meteorological conditions mainly negatively by ventilation index. • Residential heating affected HOA and LO-OOA concentrations. • CCOA has helped to refine the determination of OA sources. • EBC sf was more likely from local sources whereas eBC lf was from long-range transport. [ABSTRACT FROM AUTHOR]

The paper presents the results of the morphological study of aerosol particles in the urban air of Moscow (Russia) in 2019–2022 by scanning electron microscopy (SEM). Our monitoring revealed mineral and anthropogenic particles, and also primary bioaerosols (PBA), such as pollen, spores, plant fibers, etc., typical for the urban environment. Moreover, in July 2021, brochosomes, lipid secretions of semi-hard-winged insects Cicadellidae (or leafhopper), were found in several aerosol samples. They are quasi-spherical hollow porous semi-regular polyhedra (truncated icosahedra) of 0.2–0.7 microns in size, consisting mainly of carbon and oxygen. Despite the prevalence and diversity of leafhoppers, identification of their secretions in atmospheric aerosols in situ is rather rare: single articles from South Korea, Spain, the Himalayas, and the United States. In this sense, the results obtained are interesting and novel. PBA particles cover a wide size range and have a complex and diverse shape, which determines the distance and efficiency of their atmospheric transport. Pollen and fungal spores have a high allergenic potential and can have harmful effects on human health. Any new information about PBA can be useful for studying the development and dynamics of ecosystems. [ABSTRACT FROM AUTHOR]

In this paper, we consider two reasonable approaches to the problem of numerical simulation of the concentration distribution of a finely dispersed aerosol in spiral vortex structures (rolls) at the atmospheric boundary layer in order to estimate the contribution of vortex structures to the transport of aerosols through the boundary layer. Using the methods of perturbation theory, an approximate solution of a stationary spatially periodic singularly perturbed problem of the reaction–diffusion–advection type, which models the distribution of an aerosol in vortices, is obtained, the residual term is estimated, and a method for numerically solving the zero-approximation problem is proposed. As an alternative approach to the problem of numerical modeling of an aerosol-concentration field in rolls, implementation of the method of evolutionary factorization is considered. Using model data, an estimate of the amount of an aerosol carried by vortex structures is obtained. [ABSTRACT FROM AUTHOR]

Atmospheric boundary layer (ABL) structure was a crucial factor in altering the vertical aerosol distribution and modulating the impact of regional aerosol transport on the atmospheric environment in the receptor region. The long-term characteristics of ABL structures for different vertical aerosol distributions and the distinct influencing mechanisms between daytime and nighttime aerosol transport interacting with the diurnal ABL transition have rarely been studied in the receptor regions. Based on 9-year (2013–2021) satellite-retrieved profiles of aerosol extinction coefficients and meteorological sounding data, we targeted Wuhan, an urban city with noteworthy transport contribution in central China, to reveal the general wintertime transport height of ∼500 m and the corresponding unstable ABL structure during regional transport. By comparing typical daytime and nighttime aerosol transport with high-resolution Lidar observations, the aerosol transport near the ABL top coupled with intense mechanical mixing provided sufficient meteorological conditions for heavy aerosol pollution formation in the receptor regions, which was more favorable during nighttime transport followed by the adequate ABL development after sunrise. These findings enhance our comprehension of the ABL impact on air pollution in the receptor regions, which have implications for the precise prevention and control of the regional atmospheric environment. [Display omitted] • Aerosols were generally transported with unstable ABL structures in Wuhan. • Aerosol transport near ABL top with mechanical mixing accelerated aerosol pollution. • Nocturnal transport with daytime ABL development deteriorated aerosol pollution. [ABSTRACT FROM AUTHOR]

The dramatic shrinkage of the Aral Sea in the past decades has inevitably led to an environmental calamity. Existing knowledge on the variations and potential transport of atmospheric aerosols from the Aral Sea Basin (ASB) is limited. To bridge this knowledge gap, this study tried to identify the variations and long-range transport of atmospheric aerosols from the ASB in recent years. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data were used to gain new insight into the types, variation and long-range transport of atmospheric aerosols from the ASB. The results showed five types of tropospheric aerosols and one type of stratospheric aerosol were observed over the ASB. Polluted dust and dust were the dominant subtypes through the year. Sulfate/other was the only stratospheric aerosol detected. The occurrence frequency of aerosols over the ASB showed obvious seasonal variation. Maximum occurrence frequency of dust appeared in spring (MAM) and that of polluted dust peaked in summer (JJA). The monthly occurrence frequency of dust and polluted dust exhibited unimodal distribution. Polluted dust and dust were distributed over wide ranges from 1 km to 5 km vertically. The multi-year average thickness of polluted dust and dust layers was around 1.3 km. Their potential long-range transport in different directions mainly impacts Uzbekistan, Turkmenistan, Kazakhstan and eastern Iran, and may reach as far as the Caucasus region, part of China, Mongolia and Russia. Combining aerosol lidar, atmospheric climate models and geochemical methods is strongly suggested to gain clarity on the variations and long-range transport of atmospheric aerosols from the Aral Sea Basin. [ABSTRACT FROM AUTHOR]

Variations in the carbonaceous aerosol contents, organic carbon (OC) and elemental carbon (EC), in particulate matter less than 10 μm in size (PM10), were analyzed at sites influenced by coal mining in an open-pit mine located in northern Colombia. Samples were collected during different seasonal periods throughout 2015. Meteorological variables for each site were examined during the different seasons. Aerosols were detected using a thermal-optical reflectance protocol method. The highest PM10 concentrations, between the ranges of 28.2 ± 8.2 μg m−3 and 75.0 ± 36.5 μg m−3, were recorded during the dry season. However, the highest concentrations of OC (4.8–14.2 μg m−3) and EC (2.9–13.9 μg m−3) in PM10 were observed during the transition period between the dry and wet seasons. The strong correlation between OC and EC in PM10 (r = 0.6–1.0) during the transition season indicates a common primary combustion source. High OC (> 8.3 μg m−3) and EC (> 6.9 μg m−3) concentrations were associated with low wind speeds (< 2.1 m s−1) moving in different directions. Analyses of the sources of atmospheric aerosol pollutants in the mining area in northern Colombia showed that the daily maximum total carbon concentrations were mainly associated with regional atmospheric transport of particulate matter from industrial areas and biomass burning sites located in the territory of Venezuela. [ABSTRACT FROM AUTHOR]

During 2020–2021, a comprehensive experiment was conducted to study the composition of near-surface atmospheric aerosol in Moscow. The paper considers the experimental data together with synoptic and meteorological conditions. Attention is focused on six episodes of extremely high aerosol mass concentration values: in March and October 2020, as well in March, April, May and July 2021. In all these cases (and only in them), the average daily mass concentration of PM10 aerosol exceeded the Maximum Permissible Concentration (MPC) value (according to Russian standards, 60 μg/m3). The origin of the aerosol during these periods of extreme pollution is revealed, which is the main result of the work. It was shown that the July episode of 2021 was associated with a local intensive anthropogenic source that arose as a result of the active dismantling and demolition of multistory industrial buildings. The remaining spring and autumn episodes were caused by atmospheric transport of both smoke aerosol from various regions with strong biomass fires and dust aerosol from arid zones of the south of European territory of Russia (ETR) with dust wind storms. The cases of atmospheric pollution transport to Moscow region from the other regions are confirmed with the help of air mass transport trajectories (HYSPLIT 4 model) and MERRA-2 reanalysis data on black carbon and/or dust distribution in the atmosphere over ETR. Differences in the elemental composition of the near-surface aerosol of Moscow air during periods with extremely high aerosol concentrations are analyzed in comparison with each other and with unperturbed conditions for the season. [ABSTRACT FROM AUTHOR]

Dissolved and particulate sodium, magnesium and calcium are analyzed in ice cores to determine past changes in sea ice extent, terrestrial dust variability and atmospheric aerosol transport efficiency. They are also used to date ice cores if annual layers are visible. Multiple methods have been developed to analyze these important compounds in ice cores. Continuous flow analysis (CFA) is implemented with instruments that sample the meltstream continuously. In this study, CFA with ICP-MS (inductively coupled-plasma mass spectrometry) and fast ion chromatography (FIC) methods are compared for analysis of sodium and magnesium. ICP-MS, FIC and fluorescence methods are compared for analysis of calcium. Respective analysis of a 10 m section of the Antarctic WACSWAIN Skytrain Ice Rise ice core shows that all of the methods result in similar levels of the compounds. The ICP-MS method is the most suitable for analysis of the Skytrain ice core due to its superior precision (relative standard deviation: 1.6% for Na, 1.3% for Mg and 1.2% for Ca) and sampling frequency compared to the FIC method. The fluorescence detection method may be preferred for calcium analysis due to its higher depth resolution (1.4 cm) relative to the ICP-MS and FIC methods (~4 cm). [ABSTRACT FROM AUTHOR]

To demonstrate a synergy between radionuclide (RN) and infrasound observations and Atmospheric Transport Modelling (ATM), the volcanic activity of Bogoslof in Alaska, USA, is used as an example. The study period covers 3 months of intense eruptive activity, from 19 December 2016 to 8 March 2017. During that period, the International Monitoring System (IMS) infrasound station located in Alaska, USA, recorded signals from three eruptive sequences. The second sequence was reported in the International Data Centre (IDC) Reviewed Event Bulletin (REB) with 3 infrasound stations: in Alaska, USA, in Kamchatka, Russian Federation and in Hawaii, USA. As reported by The Alaska Volcano Observatory (AVO), during each of these events ash plumes reaching the altitude of more than 10 km were observed for several consecutive days. These observations were used to identify the length of each eruptive episode. To demonstrate the influence of volcanic ash on the berillium-7 (Be-7) activity concentration values measured by two IMS RN stations in Alaska, the ATM was used. To monitor the arrival time of a volcanic ash plume at the IMS stations, a series of 14 days forward simulations released daily from Bogoslof during each of these events, was generated. Comparison of Be-7 daily surface values with the seasonal median for the period of 9 years (2009–2017), revealed that an influx of volcanic ash up to the tropopause (1.5–12 km) tends to locally increase surface Be-7 concentrations in area under the influence of subsiding ash plume. It is also demonstrated that with the arrival of volcanic ash at the surface level, the enrichment in radioactive particulates like uranium, thorium, and potassium was observed. [ABSTRACT FROM AUTHOR]

When unaccounted for in numerical weather prediction (NWP) models, heavy aerosol events can cause significant unrealized biases in forecast meteorological parameters such as surface temperature. To improve near-surface forecasting accuracies during heavy aerosol loadings, we demonstrate the feasibility of incorporating aerosol fields from a global chemical transport model as initial and boundary conditions into a higher-resolution NWP model with aerosol–meteorological coupling. This concept is tested for a major biomass burning smoke event over the northern Great Plains region of the United States that occurred during summer of 2015. Aerosol analyses from the global Navy Aerosol Analysis and Prediction System (NAAPS) are used as initial and boundary conditions for Weather Research and Forecasting Model with Chemistry (WRF-Chem) simulations. Through incorporating more realistic aerosol direct effects into the WRF-Chem simulations, errors in WRF-Chem simulated surface downward shortwave radiative fluxes and near-surface temperature are reduced when compared with surface-based observations. This study confirms the ability to decrease biases induced by the aerosol direct effect for regional NWP forecasts during high-impact aerosol episodes through the incorporation of analyses and forecasts from a global aerosol transport model. [ABSTRACT FROM AUTHOR]

The equatorial North Atlantic Ocean (NAO) is a nutrient‐limited ecosystem that relies on the deposition of long‐range transported iron (Fe)‐containing aerosols to stimulate primary productivity. Using microscopy, we characterized supermicron and supercoarse mode African aerosols transported to the western NAO in boreal winter/spring. We detected three particle types including African dust, primary biological aerosol particles, and freshwater diatoms (FDs). FDs contained 4% Fe by weight due to surficial dust inclusions that may be susceptible to chemical processing and dissolution. FDs were typically larger than dust particles and comprised 38% of particles between 10 and 18 μm in diameter. The low density, high surface‐area‐to‐volume ratio, and large aspect ratios of FD particles suggest a mechanism by which they can be carried great distances aloft. These same properties likely increase the residence time of FDs in surface waters thereby increasing the time for Fe dissolution and their potential impact on marine biogeochemical cycles. Plain Language Summary: Atmospheric aerosols from Africa are transported by the trade winds to the western equatorial North Atlantic Ocean every winter and spring and can contain nutrients, such as iron (Fe). In this study, we measured the size and composition of supermicron (diameter (d) > 1 μm) aerosols collected at a site on the northeast coast of South America. Using electron microscopy, we found three distinct Fe‐containing particle types: mineral dust, freshwater diatoms from African paleolakes, and pollen grains; all three particle types extended into the supercoarse mode (d > 10 μm). Particle asphericity increased with increasing particle size and could explain in part the long‐range transport of supercoarse particles. Electron mapping of freshwater diatoms also revealed surficial Fe‐rich inclusions. Once deposited in the ocean, the asphericity and light density of freshwater diatom particles likely increases their residence time and therefore, the time for Fe dissolution in the surface ocean compared to dust. Key Points: Three types of iron‐containing particles were observed including freshwater diatoms that comprised 38% of particles between 10 and 18 μmAspect ratios increased with particle size suggesting asphericity may aid in transporting supercoarse particlesLow density and high aspect ratios of diatoms can increase residence times in surface waters and the likelihood of iron dissolution [ABSTRACT FROM AUTHOR]

Atmospheric transport of aerosols such as black carbon (BC) affects the absorption/scattering of solar radiation, precipitation, and snow/ice cover, especially in areas of low human activity such as the Arctic. The resolution dependency of simulated BC transport from Siberia to the Arctic, related to the well-developed low-pressure systems in September, was evaluated using the Nonhydrostatic Icosahedral Atmospheric Model-Spectral Radiation Transport Model for Aerosol Species (NICAM-SPRINTARS) with fine (~ 56 km) and coarse (~ 220 km) horizontal resolutions. These low-pressure systems have a large horizontal scale (~ 2000 km) with the well-developed central pressure located on the transport pathway from East Asia to the Arctic through Siberia. In recent years, the events analysis of the most developed low-pressure system indicated that the high-BC area in the Bering Sea observed by the Japanese research vessel Mirai on September 26 - 27, 2016, moved to the Arctic with a filamental structure from the low's center to the behind of the cold front and ahead of the warm front in relation to its ascending motion on September 27 - 28, 2016. The composite analysis for the developed low-pressure events in September from 2015 to 2018 indicated that the high-BC area was located eastward of the low's center in relation to the ascending motion over the low's center and northward/eastward area. Since the area of the maximum ascending motion has a small horizontal scale, this was not well simulated by the 220-km experiment. The study identified that the BC transport to the Arctic in September is enhanced by the well-developed low-pressure systems. The results of the transport model indicate that the material transport processes to the Arctic by the well-developed low-pressure systems are enhanced in the fine horizontal resolution (~ 56 km) models relative to the coarse horizontal resolution (~ 220 km) models. [ABSTRACT FROM AUTHOR]

Low concentrations of 106Ru were detected across Europe at the turn of September and October 2017. The origin of 106Ru has still not been confirmed; however, current studies agree that the release occurred probably near Mayak in the southern Urals. The source reconstructions are mostly based on an analysis of concentration measurements coupled with an atmospheric transport model. Since reasonable temporal resolution of concentration measurements is crucial for proper source term reconstruction, the standard 1-week sampling interval could be limiting. In this paper, we present an investigation of the usability of the newly developed AMARA (Autonomous Monitor of Atmospheric Radioactive Aerosol) and CEGAM (carousel gamma spectrometry) real-time monitoring systems, which are based on the gamma-ray counting of aerosol filters and allow for determining the moment when 106Ru arrived at the monitoring site within approx. 1 h and detecting activity concentrations as low as several mBq m -3 in 4 h intervals. These high-resolution data were used for inverse modeling of the 106Ru release. We perform backward runs of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) atmospheric transport model driven with meteorological data from the Global Forecast System (GFS), and we construct a source–receptor sensitivity (SRS) matrix for each grid cell of our domain. Then, we use our least squares with adaptive prior covariance (LS-APC) method to estimate possible locations of the release and the source term of the release. With Czech monitoring data, the use of concentration measurements from the standard regime and from the real-time regime is compared, and a better source reconstruction for the real-time data is demonstrated in the sense of the location of the source and also the temporal resolution of the source. The estimated release location, Mayak, and the total estimated source term, 237±107 TBq, are in agreement with previous studies. Finally, the results based on the Czech monitoring data are validated with the IAEA-reported (International Atomic Energy Agency) dataset with a much better spatial resolution, and the agreement between the IAEA dataset and our reconstruction is demonstrated. In addition, we validated our findings also using the FLEXPART (FLEXible PARTicle dispersion) model coupled with meteorological analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF). [ABSTRACT FROM AUTHOR]

Eastern India is characterized by high aerosol loading of primarily anthropogenic origin due to both local emissions and long-range transport and hence outflow of air mass from the Indo-Gangetic Plains. Using a year-long measurement of atmospheric aerosol optical properties over Bhubaneswar, one of the fastest growing tier-two cities in the Eastern India, we show that the aerosol optical depth (AOD) varied between 0.39 and 0.96 with high loading during February and low during July. The Angstrom exponent (AE) was found to be mostly higher than unity indicating large dominance of fine mode particles with a larger AE. Further analysis using spectral curvature of AOD and satellite-based estimates indicates that more than 80% of the time, fine mode aerosols dominate the region. It is observed that there is a large diurnal variability in AOD (AE) of the order of 15% (5%) indicating a large change in loading (spectral characteristics) over a short period of within a day. The aerosols types inferred from spectral curvature method match reasonably well with those from MERRA-2 chemical reanalysis. Further, it is found that satellite-derived AOD's are low biased with respect to ground measurements and are unable to capture seasonality consistently. These findings show that additional research is required to assess the causes for such inconsistency especially during the monsoon period. [ABSTRACT FROM AUTHOR]

The Lagrangian particle dispersion model FLEXPART in its original version in the mid-1990s was designed for calculating the long-range and mesoscale dispersion of hazardous substances from point sources, such as those released after an accident in a nuclear power plant. Over the past decades, the model has evolved into a comprehensive tool for multi-scale atmospheric transport modeling and analysis and has attracted a global user community. Its application fields have been extended to a large range of atmospheric gases and aerosols, e.g., greenhouse gases, short-lived climate forcers like black carbon and volcanic ash, and it has also been used to study the atmospheric branch of the water cycle. Given suitable meteorological input data, it can be used for scales from dozens of meters to global. In particular, inverse modeling based on source–receptor relationships from FLEXPART has become widely used. In this paper, we present FLEXPART version 10.4, which works with meteorological input data from the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS) and data from the United States National Centers of Environmental Prediction (NCEP) Global Forecast System (GFS). Since the last publication of a detailed FLEXPART description (version 6.2), the model has been improved in different aspects such as performance, physicochemical parameterizations, input/output formats, and available preprocessing and post-processing software. The model code has also been parallelized using the Message Passing Interface (MPI). We demonstrate that the model scales well up to using 256 processors, with a parallel efficiency greater than 75 % for up to 64 processes on multiple nodes in runs with very large numbers of particles. The deviation from 100 % efficiency is almost entirely due to the remaining nonparallelized parts of the code, suggesting large potential for further speedup. A new turbulence scheme for the convective boundary layer has been developed that considers the skewness in the vertical velocity distribution (updrafts and downdrafts) and vertical gradients in air density. FLEXPART is the only model available considering both effects, making it highly accurate for small-scale applications, e.g., to quantify dispersion in the vicinity of a point source. The wet deposition scheme for aerosols has been completely rewritten and a new, more detailed gravitational settling parameterization for aerosols has also been implemented. FLEXPART has had the option of running backward in time from atmospheric concentrations at receptor locations for many years, but this has now been extended to also work for deposition values and may become useful, for instance, for the interpretation of ice core measurements. To our knowledge, to date FLEXPART is the only model with that capability. Furthermore, the temporal variation and temperature dependence of chemical reactions with the OH radical have been included, allowing for more accurate simulations for species with intermediate lifetimes against the reaction with OH, such as ethane. Finally, user settings can now be specified in a more flexible namelist format, and output files can be produced in NetCDF format instead of FLEXPART's customary binary format. In this paper, we describe these new developments. Moreover, we present some tools for the preparation of the meteorological input data and for processing FLEXPART output data, and we briefly report on alternative FLEXPART versions. [ABSTRACT FROM AUTHOR]

Sea-salt aerosols (SSA) are one of the key natural aerosols in our atmosphere, consisting predominantly of sodium chloride (NaCl). Throughout their atmospheric transport, these aerosols undergo complex internal mixing, giving rise to a rich variety of inorganic and organic species, including dicarboxylic acids. This study investigates firstly the composition and deliquescence properties of coarse particles containing pure malonic acid (MA 2 , CH 2 (COOH) 2) and internally mixed NaCl and MA 2 , by means of an acoustic levitation system coupled with a Raman microspectrometer. Secondly, we report here the first experimental observation and characterization of the products arising from photochemical reactions under UV–Visible irradiation (338 ≤ λ ≤ 414 nm) in the absence of an oxidant under acoustic levitation conditions in MA 2 and NaCl/MA 2 aerosols. Furthermore, the impact of photodegradation on the hygroscopic properties of these particles is examined. We confirmed the irreversible formation of monosodium malonate (NaMA, HOOCCH 2 COONa), which coexists with NaCl or MA 2 on non-irradiated particles. We also demonstrated the formation of oxalic acid (OA 2 , HOOC–COOH) within irradiated MA 2 droplets and the appearance of glyoxylic acid (GlyA, HCOCOOH) in NaCl containing droplets. The photolysis process exerts a marked effect on the hygroscopic properties of the particles, resulting in a shift in deliquescence transitions toward higher relative humidity (RH) values. This study contributes to the understanding of the intricate physicochemical processes involved in SSA during their atmospheric transport. Likewise, this work sheds light on the impacts of these types of aerosols on cloud formation and climate change. [Display omitted] • Individual-levitated malonic acid droplets photolyzed in the absence of oxidants. • NaCl modified the photochemical reactivity of microdroplets of aqueous malonic acid. • Photolysis of malonic acid droplets produced oxalic acid or glyoxylic acid. • Photoreactivity altered deliquescence behavior and reduced hygroscopic growth. [ABSTRACT FROM AUTHOR]

An investigation into mesoscale roll circulation and its transport characteristics in the atmospheric boundary layer (ABL) is carried out. The case study of July 28, 2007, in Kalmykia, monitored during an expedition from the Obukhov Institute of Atmospheric Physics, is considered using the WRF-ARW model. The development of circulation with considerable asymmetry in the positive and negative components of the velocity field and helicity is recorded. The quasi-2D roll structures are characterized by an intensification of the dust capture and accumulation from the underlying terrain and, along with intensive vortices with a vertical axis, are a significant source of atmospheric impurities. Captured finely dispersed aerosols can be transported at long distances and form aerosol layers. [ABSTRACT FROM AUTHOR]

Abstract Using a previously developed digital gamma-gamma coincidence/anticoincidence spectrometer, daily aerosol samples collected at Resolute Bay, Canada (74.71°N, 94.97°W) from May 2016 to April 2017 were analysed for activity concentrations of 22Na and 7Be. The spectrometer design allows a more selective measurement of 22Na with a significant background reduction by gamma-gamma coincidence events processing. It has been demonstrated that the improved spectrometer provides a more sensitive and effective way to quantify trace amounts of 22Na and 7Be with a critical limit of 3 mBq and 5 Bq respectively for a 20 h counting. The 7Be/22Na ratio data set obtained in this study showed significant annual variation, which has a distinct spring (typically from February to May) maximum and winter (from September to February of next calendar year) minimum, which suggest that it could be used as a radiochronometer for studying the atmospheric processes. The 7Be/22Na ratios are most likely connected to deep stratosphere-to-troposphere transport (STT) exchange events where air with a higher 7Be/22Na ratio originates from downward flow from stratosphere to the troposphere. The aerosols with lower 7Be/22Na ratios located between two oscillation peaks may have longer residence time. The correlations between 7Be and 22Na activity concentration were the high during these time periods. Compared with other studies based on weekly collected aerosol samples, the techniques greatly improve the temporal resolution of 7Be/22Na data set that will be able to provide more detailed information to study various atmospheric phenomena. Highlights • Digital gamma-gamma coincidence/anticoincidence spectrometer was developed for routine operation. • The daily collected aerosol samples at Resolute Bay from 2016 to 2017 were analysed for the activity concentrations of 22Na and 7Be. • The 7Be/22Na ratio data set showed significant annual variation, which has a distinct spring maximum and winter minimum. • Higher correlations were observed between 7Be and 22Na in some time period indicating a longer aerosol residence time. • The techniques improve the temporal resolution for 7Be/22Na data set, provide more information to study various atmospheric phenomena. [ABSTRACT FROM AUTHOR]

Abstract Atmospheric Transport Modelling (ATM) results were combined with 7Be observations collected during the 2009–2015 period by the three radionuclide stations from the International Monitoring System (IMS), located in Mauritania (18.1 N, 15.9 W), Kuwait (29.3 N, 47.9 E) and Panama (9.0 N, 79.5 W), to study the influence of Saharan dust on changes in 7Be surface concentrations. It is demonstrated that for long-range transport (>3000 km), the overall impact of Sahara can be reproduced using a single point source located in the Bodélé depression (17.0 N, 18.0 E). To monitor the arrival time of dust plumes at the IMS stations, a series of 14-day forward simulations with daily releases from the Bodélé, during dusty episodes between 2009 and 2015, were generated. In total 1020 simulations with the output at the surface level (0–150 m) and 420 simulations with the output at 9 vertical layers ranging from the surface up to 10 km, were analysed. In the simulations, the analysed meteorological input data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) were used. It is demonstrated that an influx of dust at high levels (3–10 km) tends to locally increase surface 7Be concentrations in area under the influence of subsiding dust plume. It is also shown that an influx of dust at lower altitudes (up to 1 km) will have the opposite effect on surface concentrations. In case dust is present in the whole column of atmosphere, its final impact depends on the ratio between its amount in the upper layers (3–10 km) and lower layers (0–1 km). In consequence an increase up to 30% or a decrease up 20% in daily 7Be surface values may be observed during such an episode. On a monthly scale a few episodes related to an increase of 7Be values or its decrease may follow each other. It was estimated that on average the presence of dust leads to the increase of 7Be mean monthly surface values. The largest increase was noted at the station MRP43, of about 4.1 ± 1.3%; and the smallest at the stations KWP40, of about 2.0 ± 1.6% and PAP50, of about 2.0 ± 1.0%, respectively. Highlights • Time series of 7Be collected at 3 IMS stations are analysed over a 7-y period. • Atmospheric Transport Modelling helped explaining 7Be fluctuations at 3 IMS stations. • Vertical profile of 7Be is crucial in explaining the impact of Saharan dust. • Dust from high (low) altitudes increases (decreases) surface 7Be concentrations. • Long-range transport of Saharan dust can be approximated by a single source point. [ABSTRACT FROM AUTHOR]

Volcanic sulfate aerosol is an important source of sulfur for Antarctica, where other local sources of sulfur are rare. Midlatitude and high-latitude volcanic eruptions can directly influence the aerosol budget of the polar stratosphere. However, tropical eruptions can also enhance polar aerosol load following long-range transport. In the present work, we analyze the volcanic plume of a tropical eruption, Mount Merapi in 2010, and investigate the transport pathway of the volcanic aerosol from the tropical tropopause layer (TTL) to the lower stratosphere over Antarctica. We use the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC) and Atmospheric Infrared Sounder (AIRS) SO2 measurements to reconstruct the altitude-resolved SO2 injection time series during the explosive eruption period and simulate the transport of the volcanic plume using the MPTRAC model. AIRS SO2 and aerosol measurements, the aerosol cloud index values provided by Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), are used to verify and complement the simulations. The Lagrangian transport simulation of the volcanic plume is compared with MIPAS aerosol measurements and shows good agreement. Both the simulations and the observations presented in this study suggest that volcanic plumes from the Merapi eruption were transported to the south of 60°S 1 month after the eruption and even further to Antarctica in the following months. This relatively fast meridional transport of volcanic aerosol was mainly driven by quasi-horizontal mixing from the TTL to the extratropical lower stratosphere, and most of the quasi-horizontal mixing occurred between the isentropic surfaces of 360 to 430K. When the plume went to Southern Hemisphere high latitudes, the polar vortex was displaced from the South Pole, so that the volcanic plume was carried to the South Pole without penetrating the polar vortex. Although only 4% of the sulfur injected by the Merapi eruption was transported into the lower stratosphere south of 60°S, the Merapi eruption contributed up to 8800t of sulfur to the Antarctic lower stratosphere. This indicates that the long-range transport under favorable meteorological conditions enables a moderate tropical volcanic eruption to be an important remote source of sulfur for the Antarctic stratosphere. [ABSTRACT FROM AUTHOR]

Haze has been severely affecting the densely populated areas in China recently. While many of the efforts have been devoted to investigating the impact of local anthropogenic emission, limited attention has been paid to the contribution from long-range transport. In this study, we apply simulations from six participating models supplied through the Task Force on Hemispheric Transport of Air Pollution phase 2 (HTAP2) exercise to investigate the long-range transport impact of Europe (EUR) and Russia-Belarus-Ukraine (RBU) on the surface air quality in eastern Asia (EAS), with special focus on their contributions during the haze episodes in China. The impact of 20% anthropogenic emission perturbation from the source region is extrapolated by a factor of 5 to estimate the full impact. We find that the full impacts from EUR and RBU are 0.99µg m-3 (3.1%) and 1.32µg m-3 (4.1%) during haze episodes, while the annual averaged full impacts are only 0.35µg m-3 (1.7%) and 0.53µg m-3 (2.6%). By estimating the aerosol response within and above the planetary boundary layer (PBL), we find that long-range transport from EUR within the PBL contributes to 22-38% of the total column density of aerosol response in EAS. Comparison with the HTAP phase 1 (HTAP1) assessment reveals that from 2000 to 2010, the long-range transport from Europe to eastern Asia has decreased significantly by a factor of 2-10 for surface aerosol mass concentration due to the simultaneous emission reduction in source regions and emission increase in the receptor region. We also find the long-range transport from the Europe and RBU regions increases the number of haze events in China by 0.15% and 0.11%, and the North China Plain and southeastern China has 1-3 extra haze days (< 3%). This study is the first investigation into the contribution of long-range transport to haze in China with multi-model experiments. [ABSTRACT FROM AUTHOR]

As a southeast neighbor of the heavily industrialized and urbanized region of the Pearl River Delta (PRD), Hong Kong, China, has been susceptible to aerosols transported from the PRD in winter when the prevailing flow is from the west. The decadal trend in pollution during recent decades has likely indicated a difference in aerosol loading between winter and summer when different winds dominate. The surface air temperature shows a wintertime cooling trend during recent decades in Hong Kong, particularly during the midday hours. Differently, the surface air temperature shows a summertime warming trend during recent decades in Hong Kong. By examining the distinct winter versus summer trends in midday hour temperature under low cloud cover conditions in Hong Kong from 1979 to 2014, we found a close relationship between the temperature reduction during midday hours and increased aerosol loading in winter but not in summer. The consistency in turning point for both the increase in aerosol loading and the variation in winter-summer temperature differences in the late 1980s also supports the strong association between aerosol and temperature changes. Further analysis shows that there was a significant negative correlation between downwelling solar radiation (DSR) and aerosol loading. Quantitatively, aerosols over Hong Kong during the study period reduced surface DSR and midday temperatures by approximately 30 W m −2 and 2.1 °C for low cloud cover cases. [ABSTRACT FROM AUTHOR]

This study presents multi-year monitoring data on atmospheric polybrominated diphenyl ethers (PBDEs) in central Europe. Air was sampled on a weekly basis at a background site in the central Czech Republic from 2011 to 2014 (N = 114). Σ8PBDEs (without BDE209) total (gas and particulate) concentrations ranged from 0.084 to 6.08 p gm-3, while BDE209 was at 0.05-5.01 pg m-3. BDE47, BDE99 and BDE183 were the major contributors to Σ8PBDEs. Overall, the atmospheric concentrations of individual PBDEs were controlled by deposition processes, meteorological parameters and long-range atmospheric transport. Regarding gas--particle partitioning, with the exception of BDE28 (gaseous) and BDE209 (particulate), all congeners were consistently detected in both phases. Clear seasonal variations with significantly higher measured particulate fraction (θmeasured) in winter compared to summer was found for all PBDEs except BDE209. For example, while the average θmeasured of BDE47 was 0:53 ± 0.19 in winter, this was only 0:01 ± 0:02 in summer. Similarly, for BDE99, θmeasured was 0.89 ± 0.13 in winter, while it was only 0:12 ± 0:08 in summer. The observed gas--particle partitioning coefficient (Kp, in m³ µg-1) was compared with three model predictions, assuming equilibrium or a steady state. None of the models could provide a satisfactory prediction of the partitioning, suggesting the need for a universally applicable model. Statistically significant decreases of the atmospheric concentrations during 2011-2014 were found for BDE99, 100, 153 and 209. Estimated apparent atmospheric halving times for these congeners ranged from 2.8 (BDE209) to 4.8 (BDE153) years. The results suggest that photolytic debromination to lower brominated congeners may significantly influence PBDE concentration levels and patterns in the atmosphere. [ABSTRACT FROM AUTHOR]

A methodology utilizing multiple aerosol measurements and reanalysis was developed to analyze the long-range transport (LRT) of North African and Asian dust events and their effect on contiguous U.S. (CONUS) air quality. Two events in 2015, that originated inland from North Africa and Asia, were detected with aerosol optical depth (AOD) greater than 0.8 over the Gulf of Mexico (June 21) and west coast of Oregon and Washington (April 19). Large amounts of dust were rising over Sahara-Sahel and Taklamakan deserts during these events. For the North African dust event, dust remained the dominant aerosol species transporting from North Africa to CONUS. For Asian dust, before the Taklamakan dust outbreak traveled across the Pacific Ocean, it mixed with sulfate from East China and organic carbons from Siberia. The trans -Atlantic North African dust emerged and compressed below 5 km over the Azores High, whereas the trans -Pacific Asian dust entered the westerlies (5–10 km) along with the mid-latitude frontal system. For the two cases examined, the North African dust event tended to have more influence on CONUS air quality. During the LRT periods, there were 4 of 17 rural and suburban stations (with AOD > 0.5 as the LRT dust approached) in Texas and Louisiana reporting PM 2.5 daily maximum observations greater than 36.3 μg m −3 . In contrast, the Asian dust stayed above ground level, and all of the 4 rural and suburban stations (with AOD > 0.5 as the LRT dust approached) in Washington and Oregon observed daily maximum PM 2.5 below 22.4 μg m −3 . The integration of measurements and modeling was able to successfully characterize the sources and transport patterns of the LRT dust events, and differentiate their influence on CONUS air quality. Even though there was high AOD from the Asian LRT dust detected over the western CONUS, significant impacts on surface air quality was not observed as the dust remained aloft. [ABSTRACT FROM AUTHOR]

This study examines the role of grid resolution on particulate nitrate predictions over the Eastern US during the summer using the three-dimensional chemical transport model (CTM) PMCAMx. The Base Case simulation with coarse resolution (36 × 36 km) often predicts high nighttime nitrate production rates thus leading to overprediction of aerosol nitrate levels. This overprediction is due to the artificial mixing of NO x -rich plumes from major point and area sources with the background atmosphere. Three different horizontal grid resolutions were tested (12 × 12 km, 4 × 4 km and telescoping 12x12/4 × 4 km) for parts of the northeastern US. The bias for PM 2.5 nitrate decreased by 65% when the grid resolution was increased to 4 × 4 km. However, the remaining discrepancies between nitrate predictions and measurements indicate the need for additional improvements including better simulation of the total emissions of ammonia and their temporal evolution, improved description of nighttime chemistry and mixing etc. [ABSTRACT FROM AUTHOR]

The global distribution of aerosol optical depth (AOD) is simulated using an aerosol transport model coupled to an atmospheric general circulation model with high spatial and temporal resolution. Daily representative AOD from model simulation is estimated after consideration of observation sampling in daytime (ground-based) and overpass time (satellite) after cloud masking. Large deviations in AOD are found after considering temporally inhomogeneous sampling, with positive differences over desert regions and negative differences over anthropogenic pollution and biomass burning regions. Mean difference in daily AOD of 5.33% (standard deviation of 8.02%), because of temporal inhomogeneous sampling, is identified based on observation time information from the Moderate-Resolution Imaging Spectroradiometer (MODIS). Relative differences in AOD of >50% and >30% were found in 7.9% and 22.8% of the data, respectively. Based on the observation time information from the AERONET, relative root mean square error (rRMSE) of AOD due to temporal inhomogeneous sampling is estimated to be 4.30–18.66%. After correcting for temporal sampling inhomogeneity, the simulated global AOD was compared with AODs from MODIS and AERONET. The simulated AOD becomes lower than MODIS AOD because of emission and transport discrepancies related to dust, a limited accounting of nitrate processes, and limitation errors from MODIS AOD retrieval. A regional positive bias in SPRINTARS AOD was found in biomass burning regions, which is due to transport pattern errors related to the initial injection height of emissions. A weak correlation is found over the regions with multiple aerosol sources because of complex interactions of individual aerosol types. [ABSTRACT FROM AUTHOR]

This study investigates the production/loss of sulfate on the sea surface during its transport from Eastern China to South Korea (Korea). We use the Community Multi-scale Air Quality (CMAQ) model to simulate sulfate concentrations in February 2015 and to examine the changes in them. Results of the CMAQ simulation show high sulfate concentrations over the sea surface areas between Eastern China and Korea despite nearly zero emissions. Their concentrations gradually increased (from 0.371 to 0.581㎍/m 3 /h) as they passed through the East China Sea, the Yellow Sea, and the Korea Strait. The results from a quantitative analysis using the integrated process rate (IPR) in CMAQ suggest that increasing sulfate concentrations during the transport was mainly attributable to chemical sulfate productions by the aerosol process (up to 0.866㎍/m 3 /h) and vertical transport (up to 0.994㎍/m 3 /h) of chemically produced sulfate, resulting from vertical momentum transport caused by vertical wind shear and temperature gradient. The results of the sulfur tracking model (STM) in CMAQ verify that the OH + SO 2 → H 2 SO 4 + HO 2 reaction was the largest contributor (82.31%) to the production of sulfate over the sea surface areas during its transport. Surplus SO 2 in the transporting plume reacted to abundant OH over the sea surface, formed H 2 SO 4 , and contributed to the consequently increased sulfate concentrations. The observed sulfate data in Korea confirm that sulfate concentrations over the sea surface areas enhanced sulfate concentrations in Korea (from 12.27 to 13.74㎍/m 3 ). The sulfate, however, was not directly transported from upwind regions but chemically produced during the transport. The results of several sensitivity simulations with varied meteorology revealed that the changes in chemical sulfate production rates during the transport of sulfate were mainly affected by temperature. [ABSTRACT FROM AUTHOR]

The northeastern China frequently experiences severe aerosol pollution in winter under unfavorable meteorological conditions. How and to what extent the meteorological factors affect the air quality there are not yet clearly understood. Thus, this study investigated the impacts of synoptic patterns on the aerosol transport and planetary boundary layer (PBL) structure in Shenyang from 1 to 3 December 2016, using surface observations, sounding measurements, satellite data, and three-dimensional simulations. Results showed that the aerosol pollution occurred in Shenyang was not only related to the local emissions, but also contributed by trans-boundary transport of aerosols from the Beiijng-Tianjin-Hebei (BTH) region. In the presence of the westerly and southwesterly synoptic winds, the aerosols emitted from BTH could be brought to Shenyang. From December 2 to 3, the aerosols emitted from BTH accounted for ∼20% of near-surface PM 2.5 in Shenyang. In addition, the large-scale synoptic forcings could affect the vertical mixing of pollutants through modulating the PBL structure in Shenyang. The westerly and southwesterly synoptic winds not only brought the aerosols but also the warmer air masses from the southwest regions to Shenyang. The strong warm advections above PBL could enhance the already existing thermal inversion layers capping over PBL in Shenyang, leading to the suppressions of PBL. Both the trans-boundary transport of aerosols and the suppressions of PBL caused by the large-scale synoptic forcings should be partly responsible for the poor air quality in Shenyang, in addition to the high pollutant emissions. The present study revealed the physical mechanisms underlying the aerosol pollution in Shenyang, which has important implications for better forecasting and controlling the aerosols pollution. [ABSTRACT FROM AUTHOR]

ABSTRACT: Daily measurements of aerosol optical depth (τ) and Ångstrom wavelength exponent (α) acquired from Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectrometer (MODIS) are analysed over Lahore – an urban city of Pakistan (period: 2010–2014) to investigate contribution of different types of aerosols originating from both local and regional source locations. The obtained annual averages (mean ± standard deviation) for AERONET retrievals of τ (500 nm) and α (440–870 nm) are 0.68 ± 0.37 (0.08–2.91) and 0.99 ± 0.33 (0–1.8), respectively. Of all the sources, 61% are found within Pakistan, 11% in India, 19% in Afghanistan, 6% in Iran and 2% in Saudi Arabia with seasonal contributions of 35, 25, 23 and 17% in pre‐monsoon, monsoon, winter and post‐monsoon, respectively. The bimodal distributions of α show dominance of coarse‐mode particles during pre‐monsoon, fine‐mode particles during post‐monsoon and presence of both coarse‐mode and fine‐mode particles during winter and monsoon with winter showing more fine‐mode particles. Two broad classes of aerosols namely desert dust (DD) and biomass burning/urban industrial (BU) are identified with criteria, e.g. τ ≥ 0.3 and α ≤ 0.75 indicating presence of DD while τ ≥ 0.2 and α ≥ 1.15 indicating BU. The frequency of occurrence (FOO) of DD and BU aerosols is further identified by applying classification criteria over Aqua‐MODIS deep blue retrievals. The FOO identifies anthropogenic activity on‐going throughout the year, disrupted with DD aerosols only during pre‐monsoon and monsoon. The maximum dust activity is seen over Indo‐Gangetic plains (IGP) (localized maxima: 35–45%) and the Arabian peninsula (>55%) during pre‐monsoon, while maximum BU aerosols are found over IGP, central and south‐eastern plains of India and the state of Gujarat (localized maxima: >70%) in winter and post‐monsoon. [ABSTRACT FROM AUTHOR]

Sedimentary plant wax 2 H/ 1 H ratios are important tools for understanding hydroclimate and environmental changes, but large spatial and temporal uncertainties exist about transport mechanisms from ecosystem to sediments. To assess atmospheric pathways, we collected aerosol samples for two years at four locations within a ∼60 km radius in northern Switzerland. We measured n -alkane distributions and 2 H/ 1 H ratios in these samples, and from local plants, leaf litter, and soil, as well as surface sediment from six nearby lakes. Increased concentrations and 2 H depletion of long odd chain n -alkanes in early summer aerosols indicate that most wax aerosol production occurred shortly after leaf unfolding, when plants synthesize waxes in large quantities. During autumn and winter, aerosols were characterized by degraded n -alkanes lacking chain length preferences diagnostic of recent biosynthesis, and 2 H/ 1 H values that were in some cases more than 100‰ higher than growing season values. Despite these seasonal shifts, modeled deposition-weighted average 2 H/ 1 H values of long odd chain n -alkanes primarily reflected summer values. This was corroborated by n -alkane 2 H/ 1 H values in lake sediments, which were similar to deposition-weighted aerosol values at five of six sites. Atmospheric deposition rates for plant n -alkanes on land were ∼20% of accumulation rates in lakes, suggesting a role for direct deposition to lakes or coastal oceans near similar production sources, and likely a larger role for deposition on land and transport in river systems. This mechanism allows mobilization and transport of large quantities of recently produced waxes as fine-grained material to low energy sedimentation sites over short timescales, even in areas with limited topography. Widespread atmospheric transfer well before leaf senescence also highlights the importance of the isotopic composition of early season source water used to synthesize waxes for the geologic record. [ABSTRACT FROM AUTHOR]

Multiple year-round records of bulk and sizesegregated composition of aerosol were obtained at the inland site of Concordia located at Dome C in East Antarctica. In parallel, sampling of acidic gases on denuder tubes was carried out to quantify the concentrations of HCl and HNO3 present in the gas phase. These time series are used to examine aerosol present over central Antarctica in terms of chloride depletion relative to sodium with respect to freshly emitted sea-salt aerosol as well as depletion of sulfate relative to sodium with respect to the composition of seawater. A depletion of chloride relative to sodium is observed over most of the year, reaching a maximum of ~20 ngm-3 in spring when there are still large sea-salt amounts and acidic components start to recover. The role of acidic sulfur aerosol and nitric acid in replacing chloride from sea-salt particles is here discussed. HCl is found to be around twice more abundant than the amount of chloride lost by sea-salt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or re-emission from the snow pack over the Antarctic plateau represents an additional significant HCl source. The size-segregated composition of aerosol collected in winter (from 2006 to 2011) indicates a mean sulfate to sodium ratio of sea-salt aerosol present over central Antarctica of 0.16±0.05, suggesting that, on average, the sea-ice and open-ocean emissions equally contribute to sea-salt aerosol load of the inland Antarctic atmosphere. The temporal variability of the sulfate depletion relative to sodium was examined at the light of air mass backward trajectories, showing an overall decreasing trend of the ratio (i.e., a stronger sulfate depletion relative to sodium) when air masses arriving at Dome C had traveled a longer time over sea ice than over open ocean. The findings are shown to be useful to discuss sea-salt ice records extracted at deep drilling sites located inland Antarctica. [ABSTRACT FROM AUTHOR]

The global source-receptor relationships of sulfate concentrations, and direct and indirect radiative forcing (DRF and IRF) from 16 regions/sectors for years 2010-2014 are examined in this study through utilizing a sulfur source-tagging capability implemented in the Community Earth System Model (CESM) with winds nudged to reanalysis data. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. Regional source efficiencies of sulfate concentrations are higher over regions with dry atmospheric conditions and less export, suggesting that lifetime of aerosols, together with regional export, is important in determining regional air quality. The simulated global total sulfate DRF is -0.42W m-2, with -0.31 W m-2 contributed by anthropogenic sulfate and -0.11 W m-2 contributed by natural sulfate, relative to a state with no sulfur emissions. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17-84 % to the total DRF. East Asia has the largest contribution of 20-30 % over the Northern Hemisphere mid- and high latitudes. A 20 % perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of -0.44 W m-2. DMS has the largest contribution, explaining -0.23 W m-2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than that over the polluted Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Size-resolved aerosol samples from the Shanghai atmosphere were analyzed for normal alkanes ( n -alkanes, C 8 –C 40 ) by comprehensive two-dimensional gas chromatography–flame ionization detection and gas chromatography–triple quadruple mass spectroscopy to study their size distribution and contributions from potential regional sources based on a one-year (2012 − 2013) sampling campaign. The n -alkane concentrations ranged from 62.3 to 398.5 ng m − 3 , with an annual average of 227.6 ng m − 3 . Particle-associated n -alkanes exhibited a bimodal distribution with one peak in the accumulation-mode size range and the other in the coarse-mode size range. As the carbon number increased, the peak in the accumulation mode intensified and the peak in the coarse mode weakened, in accordance with variation of their corresponding volatilities. Source indices (carbon preference index, average chain length, odd-even carbon number preference, unresolved to resolved n -alkanes ratio, and plant wax n -alkanes ratio) indicated that the n -alkane source profile shifted from an anthropogenic-dominated pattern in winter and spring to a terrestrial plant wax-influenced pattern in summer and autumn. Further trajectory cluster analysis and potential source contribution function modeling showed that anthropogenic activities were mainly in the North China Plain and East China and that terrestrial plant waxes originated in Anhui, Zhejiang, and Jiangxi Provinces. The results of our study provide useful information for evaluating the influence of anthropogenic and biogenic activities on the atmospheric transport of important secondary organic aerosol precursors to megacities in East Asia. [ABSTRACT FROM AUTHOR]

During the CalWater 2015 field campaign, ground-level observations of aerosol size, concentration, chemical composition, and cloud activity were made at Bodega Bay, CA, on the remote California coast. A strong anthropogenic influence on air quality, aerosol physicochemical properties, and cloud activity was observed at Bodega Bay during periods with special weather conditions, known as Petaluma Gap flow, in which air from California's interior is transported to the coast. This study applies a diverse set of chemical, cloud microphysical, and meteorological measurements to the Petaluma Gap flow phenomenon for the first time. It is demonstrated that the sudden and often dramatic change in aerosol properties is strongly related to regional meteorology and anthropogenically influenced chemical processes in California's Central Valley. In addition, it is demonstrated that the change in air mass properties from those typical of a remote marine environment to properties of a continental regime has the potential to impact atmospheric radiative balance and cloud formation in ways that must be accounted for in regional climate simulations. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present an overview of inverse modeling methods that have been developed over the years for estimating the global sources and sinks of CH4. It provides insight into how techniques and estimates have evolved over time and what the remaining shortcomings are. As such, it serves a didactical purpose of introducing apprentices to the field, but it also takes stock of developments so far and reflects on promising new directions. The main focus is on methodological aspects that are particularly relevant for CH4, such as its atmospheric oxidation, the use of methane isotopologues, and specific challenges in atmospheric transport modeling of CH4. The use of satellite retrievals receives special attention as it is an active field of methodological development, with special requirements on the sampling of the model and the treatment of data uncertainty. Regional scale flux estimation and attribution is still a grand challenge, which calls for new methods capable of combining information from multiple data streams of different measured parameters. A process model representation of sources and sinks in atmospheric transport inversion schemes allows the integrated use of such data. These new developments are needed not only to improve our understanding of the main processes driving the observed global trend but also to support international efforts to reduce greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Measurements of size-resolved aerosols from 0.25 to 18 µm were conducted at three sites (urban, suburban and background sites) and used in tandem with an atmospheric transport model to study the size distribution and formation of atmospheric aerosols in southern China during the monsoon season (May-June) in 2010. The mass distribution showed the majority of chemical components were found in the smaller size bins (< 2.5 µm). Sulfate was found to be strongly correlated with aerosol water and anticorrelated with atmospheric SO2, hinting at aqueous-phase reactions being the main formation pathway. Nitrate was the only major species that showed a bimodal distribution at the urban site and was dominated by the coarse mode in the other two sites, suggesting that an important component of nitrate formation is chloride depletion of sea salt transported from the South China Sea. In addition to these aqueous-phase reactions and interactions with sea salt aerosols, new particle formation, chemical aging, and long-range transport from upwind urban or biomass burning regions was also found to be important in at least some of the sites on some of the days. This work therefore summarizes the different mechanisms that significantly impact the aerosol chemical composition during the monsoon over southern China. [ABSTRACT FROM AUTHOR]

By employing PM 2.5 observation data, ground-based lidar measurements, MODIS and CALIPSO satellite images, meteorological data, and back trajectories analysis, we investigate a trans-boundary transport of aerosols during a large-area haze episode in China during 3–5 January 2015. The ground-based lidar observations indicated similar episodes of external aerosols passing through and mixing into three East China cities. A considerable amount of total AOD below 3 km (46% in average) was contributed by the external aerosol layers during passing over and importing. CALIPSO satellite observations of central and eastern China revealed a high altitude pollutant belt on January 3. Although the severest ground pollution was found in central and south-eastern Hebei, the high altitude pollution transport was greater in south-western Shandong, north-western Jiangsu, and north-western Anhui. These observations along with the analysis of air mass trajectories and wind fields indicates pollutants moving from Hebei, Henan and Hubei probably contributed to the haze pollution in Shandong and Jiangsu. This study reveals haze transports from North China Plain to East China could be a common phenomenon influenced by the winter monsoon in northern China. Hence, effective control of air pollution requires collaboration among different cities and provinces throughout China. The long-term measurements of aerosol vertical properties by ground-based lidar and CALIPSO are extremely valuable in quantifying the contributions of external factors and will be helpful in validating and improving various air quality models. [ABSTRACT FROM AUTHOR]