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

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

In this study, a global variable‐resolution modeling framework of atmospheric dust and its radiative feedback is established and evaluated. In this model, atmospheric dust is simulated simultaneously with meteorological fields, and dust‐radiation interactions are included. Five configurations of global mesh with refinement at different resolutions and over different regions are used to explore the impacts of regional refinement on modeling dust lifecycle at regional and global scales. The model reasonably produces the overall magnitudes and spatial variabilities of global dust metrics such as surface mass concentration, deposition, aerosol optical depth, and radiative forcing compared to observations and previous modeling results. Two global variable‐resolution simulations with mesh refinement over major deserts of North Africa (V16 km‐NA) and East Asia (V16 km‐EA) simulate less dust emissions and smaller dry deposition rates inside the refined regions due to the weakened near‐surface wind speed caused by better resolved topographic complexity at higher resolution. The dust mass loadings over North Africa are close to each other between V16 km‐NA and the quasi‐uniform resolution (∼120 km) (U120 km), while over East Asia, V16 km‐EA simulates higher dust mass loading. Over the non‐refined areas with the same resolution, the difference between global variable‐resolution and uniform‐resolution experiments also exists, which is partly related to their difference in dynamic time‐step and the coefficient for horizontal diffusion. Refinement at convection‐permitting resolution around the Tibetan Plateau (TP) simulates less dust due to its more efficient wet scavenging from resolved convective precipitation around the TP against coarse resolution. Plain Language Summary: Mineral dust plays an important role in Earth's climate system. Numerical simulation of dust and its impacts on a regional scale still has large uncertainties, partly due to the relatively coarse horizontal resolution. Limited‐area simulation at relatively high resolution can generally better characterize dust and its impacts on a regional scale; however, lateral boundary conditions may introduce some numerical issues and constrain regional feedback, such as dust‐cloud and dust‐radiation interactions, to large‐scale circulation. In this study, a novel modeling framework of atmospheric dust and its climatic feedbacks with the capability of global variable‐resolution simulation is established and evaluated. The model produces reasonable global spatial distributions of dust compared to observations and previous studies. The difference between the simulations at global quasi‐uniform resolution and global variable resolution with regional refinement over East Asia and North Africa is significant, particularly with refinement at convection‐permitting resolution. This model may be used in the future to provide new insights into the impacts of dust on regional and global climate systems. Key Points: A modeling framework of atmospheric dust with the capability of global variable‐resolution simulation is introduced and evaluatedExperiments with regional refinement produce less dust emissions and mass loading and smaller dry deposition due to weaker surface windRefinement at convection‐permitting resolution simulates stronger wet scavenging and less dust mass compared to coarse resolution [ABSTRACT FROM AUTHOR]

Mineral dust affects health, climate, and ecosystems in various ways. East Asia is one of the major sources of mineral dust worldwide. This study examines the year-to-year variability of dust deposition over Japan in April from the perspective of large-scale atmospheric circulations using atmospheric and aerosol reanalysis datasets for the period from 2011 to 2017. The increased dust deposition in Japan is explained by the intensified dust transport from the Mongolian Plateau by the anomalous westerly winds associated with a deepened trough over the East Asian continent toward the northwest of the Japanese islands in the middle to lower troposphere. The enhanced dust emission over the Gobi Desert and the intensified extratropical cyclone activity are consistent with the largerthan-normal dust amount in East Asia. Comparing the dust depositions over western and northern Japan, it is suggested that the slightly different anomalous trough positions may determine whether or not a large amount of dust is carried. A further analysis using the long-term (1967 - 2022) observation data of dust in Japan supports the importance of the intensified trough over the East Asian continent. Dust flux decomposed into cyclonic and anticyclonic components showed that both vortices contribute to the eastward dust transport in East Asia. These results suggest that Japanese dust events and their variability are affected by the stationary circulation anomaly as well as the baroclinic instability waves including transient cyclones and anticyclones. [ABSTRACT FROM AUTHOR]

As a natural aerosol with the largest emissions on land, dust has important impacts on the atmospheric environment and climate systems. Both the emissions and transport of dust aerosols are tightly connected to meteorological conditions and as a result are confronted with strong modulations by the changing climate. Here, we project the changes in the global dust emissions and loading by the end of the 21st century, using an ensemble of model outputs from the Coupled Model Intercomparison Project version 6 (CMIP6) under four Shared Socioeconomic Pathways (SSPs). Based on the validations against site-level observations, we select 9 out of 14 models and estimate an ensemble global dust emissions of 2566 ± 1996 Tga-1 (1 Tg = 10 12 g) for the present day, in which 68 % is dry deposited and 31 % is wet deposited. Compared to 2005–2014, global dust emissions show varied responses, with a reduction of - 5.6 ± 503 Tga-1 under the SSP3–7.0 scenario but increased emissions up to 60.7 ± 542 Tga-1 under the SSP5–8.5 scenario at 2090–2099. For all scenarios, the most significant increase in the dust emissions appears in North Africa (0.6 %–5.6 %) due to the combined effects of reduced precipitation but strengthened surface wind. In contrast, all scenarios show decreased emissions in the Taklimakan and Gobi deserts (- 0.8 % to - 11.9 %) because of the increased precipitation but decreased wind speed on a regional scale. The dust loading shows uniform increases over North Africa (1.6 %–13.5 %) and the downwind Atlantic, following the increased emissions but decreases over East Asia (- 1.3 % to - 10.5 %), and the downwind Pacific, partly due to enhanced local precipitation that promotes wet deposition. In total, global dust loading will increase by 2.0 %–12.5 % at the end of the 21st century under different climate scenarios, suggesting a likelihood of strengthened radiative and climatic perturbations by dust aerosols in a warmer climate. [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]

Acting as efficient ice‐nucleating particles, dust particles can affect cirrus cloud properties through heterogeneous nucleation. A dust‐infused baroclinic storm (DIBS) over East Asia in May 2017 was examined using satellite observations and the Weather Research and Forecasting model coupled with chemistry (WRF‐Chem) to study the dust effects on cirrus clouds. Satellite observations showed that the ice number concentration (Nice) was extremely high, exceeding 1–10 cm−3 at the cirrus shield of the DIBS, and the ice effective radius (rei) was about 10–30 μm. An aerosol‐aware heterogeneous ice nucleation parameterization (Ullrich et al., 2017, https://doi.org/10.1175/jas-d-16-0074.1) was implemented into WRF‐Chem to explore the formation mechanism of such a high Nice. The simulated Nice from Ullrich17 was 1–2 orders of magnitude higher than that from the default scheme (Cooper, 1986, https://doi.org/10.1007/978-1-935704-17-1%5f4), and the rei was 2–3 times smaller. The results from Ullrich17 were more consistent with satellite observations, which can be attributed to the enhanced deposition nucleation from the high dust concentrations. Our results demonstrated that the extremely high Nice could be fully explained by the heterogeneous nucleation of dust particles in DIBS. A conceptual framework is proposed to explain the dust‐cloud interactions in DIBS. This study confirms the significant dust effects on cirrus clouds in DIBS and highlights the importance of using aerosol‐aware ice nucleation parameterizations in modeling cirrus clouds when the dust is present. Plain Language Summary: Cirrus clouds have a significant impact on the Earth's radiative budget and climate. Dust particles are efficient ice nucleating particles for enabling the ice formation process in cirrus clouds. We found extremely high ice number concentrations at the top cirrus shield of dust‐infused extratropical cyclone clouds using satellite observations. To understand how such high concentrations of ice crystals form, we implemented an aerosol‐aware ice nucleation parameterization into a regional chemistry‐climate model. The simulated ice number concentration and ice effective radius were significantly improved when using the newly added ice nucleation scheme. According to satellite observations and model results analysis, we proposed a conceptual framework for the formation mechanism of such high ice concentrations. Dust particles were transported to the altitude of the cirrus shield through the warm conveyor belt, and numerous ice crystals were formed from the deposition nucleation on dust particles with the consumption of water vapor. This study confirms the significant dust effects on cirrus shields in dust‐infused extratropical cyclone clouds. Future modeling work on cirrus clouds associated with dust should take the aerosol effects into account. Key Points: Extremely high concentrations of ice particles in dust‐infused baroclinic storm (DIBS) cirrus shield by the heterogeneous deposition nucleation of dust particles were foundThe importance of aerosol‐aware ice nucleation parameterizations in modeling dust‐cloud interactions within DIBS was demonstratedThe conceptual framework is proposed to explain the dust‐cloud interactions in DIBS [ABSTRACT FROM AUTHOR]

Approximately 50% of the Earth's deserts are covered with stony surfaces, not dunes. The stony surfaces often block or diminish mineral dust aerosol emissions through area fraction and roughness element effects. Incorporating these stone coverage effects is crucial for climate and environmental modeling research. Based on our field observations, this study combined the stone coverage effects into a dust simulation model for East Asia using two regression formulas and some constants. The double regression scheme assumed that the stone roughness density could be derived from the coarse fragment fraction of the SoilGrids 2.0 data set. According to the data set, the stone coverage is higher in Western Mongolia and Dzungaria and lower in the Chinese Gobi Desert and the Loess Plateau. Consequently, the model reproduced fewer dust aerosols in the higher coverage areas and more in the lower coverage areas. This simulation result was consistent with the World Meteorological Organization's current weather reports and satellite aerosol observations. The improved model reproduced the diversity of soil erodibility and was well balanced in performance statistics. This study is the first successful investigation of stone coverage effects on dust storm simulation using a realistic stone coverage map to the authors' best knowledge. Plain Language Summary: More than 50% of the Earth's deserts are covered with stones, not dunes. The stony surfaces suppress sand and dust storms in the deserts. Because the mineral dust particles globally influence climate change, investigating the stony surfaces is crucial to climate prediction research. Therefore, we developed a new simulation scheme for sand and dust storms to incorporate the stony surface effects. Formulating the stony surface effects was based on our field observations in East Asia. The global stone map we used was obtained from the SoilGrids 2.0 data set. Our simulation model reproduced fewer dust storms in higher stone coverage areas and more in lower areas. This simulation result was consistent with weather observatory observations in Mongolia and China. Satellite measurements for air pollution also backed up the simulation result. This study is the first successful investigation of the stony surface effects on dust storm simulations using a realistic stone coverage map to the authors' best knowledge. Key Points: Stony surfaces of drylands significantly affect dust aerosol emissions through area fraction and roughness element effectsA dust simulation model incorporated the stone coverage effects with an actual soil/stone mapThe conversion function from the stone coverage to the stone roughness density was derived from field observations in the Gobi Desert [ABSTRACT FROM AUTHOR]

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

East Asia is the second-largest mineral dust source in the world, after the Sahara. When dispersed in the atmosphere, mineral dust can alter the Earth's radiation budget by changing the atmosphere's absorption and scattering properties. Therefore, the mineralogical composition of dust is key to understanding the impact of mineral dust on the atmosphere. This paper presents new information on mineralogical dust during East Asian dust events that were obtained from laboratory dust measurements combined with satellite remote sensing dust detections from the Infrared Atmospheric Sounding Interferometer (IASI). However, the mineral dust in this region is lifted above the continent in the lower troposphere, posing constraints due to the large variability in the Land Surface Emissivity (LSE). First, a new methodology was developed to correct the LSE from a mean monthly emissivity dataset. The results show an adjustment in the IASI spectra by acquiring aerosol information. Then, the experimental extinction coefficients of pure minerals were linearly combined to reproduce a Gobi dust spectrum, which allowed for the determination of the mineralogical mass weights. In addition, from the IASI radiances, a spectral dust optical thickness was calculated, displaying features identical to the optical thickness of the Gobi dust measured in the laboratory. The linear combination of pure minerals spectra was also applied to the IASI optical thickness, providing mineralogical mass weights. Finally, the method was applied after LSE optimization, and mineralogical evolution maps were obtained for two dust events in two different seasons and years, May 2017 and March 2021. The mean dust weights originating from the Gobi Desert, Taklamakan Desert, and Horqin Sandy Land are close to the mass weights in the literature. In addition, the spatial variability was linked to possible dust sources, and it was examined with a backward trajectory model. Moreover, a comparison between two IASI instruments on METOP-A and -B proved the method's applicability to different METOP platforms. Due to all of the above, the applied method is a powerful tool for exploiting dust mineralogy and dust sources using both laboratory optical properties and IASI detections. [ABSTRACT FROM AUTHOR]

Mineral dust affects global and regional climates through radiative forcing. Herein the relationship between convective mixed layers and dust weather over arid and semi‐arid regions in East Asia is statistically analysed using operational surface‐station observation data and the lifting condensation level (LCL) height as a substitute for the mixed layer height. We divided the East Asia area into five regions (west/east Taklamakan Desert, west/east Gobi Desert and northeast China) and classified dust weather into three categories (floating dust, blowing dust and dust storm). Floating dust is the most frequent in the west Taklamakan Desert. All dust weather types are observed in the Taklamakan Desert even at low wind speeds but are seldom observed if the daily maximum LCL height is less than about 1,000 m. The floating dust events observed inside the Tarim basin seem to spread widely. In the Gobi Desert, when the maximum LCL height reaches about 3,000 m, all the dust weather types spread within the region. In all regions, the daily maximum LCL heights are higher in dust weather categories than in the no‐dust weather category. When a severe dust weather is observed in the Taklamakan and Gobi Deserts, the daily maximum LCL height reaches around 4,000–5,000 m above the mean sea level under higher wind conditions, suggesting that dust particles are easily raised from the boundary layer into the free troposphere during dust events in well‐developed mixed layer conditions. In the Gobi region, the frequency and areal extent of the blowing dust and the dust storm are higher than those of the floating dust. Therefore, the role of the deep mixed layers in the Gobi Desert is more important than that in the Taklamakan Desert. [ABSTRACT FROM AUTHOR]

Central Asia is one of the most important sources of mineral saline dust worldwide. A comprehensive understanding of Central Asian dust transport is essential for evaluating its impacts on human health, ecological safety, weather and climate. This study first puts forward an observation-based climatology of Central Asian dust transport flux by using the 3-D dust detection of Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP). The seasonal difference of transport flux and downstream contribution are evaluated and compared with those of the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Central Asian dust can be transported not only southward in summer under the effect of the South Asian summer monsoon, but also eastward in other seasons under the control of the westerly jet. Additionally, the transport of Central Asian dust across the Pamir Plateau to the Tibetan Plateau is also non-negligible, especially during spring (with a transport flux rate of 150 kg m−1 day−1). The annual CALIOP-based downstream contribution of Central Asian dust to South Asian (164.01 Tg) is 2.1 times that to East Asia (78.36 Tg). This can be attributed to the blocking effect of the higher terrain between Central and East Asia. Additionally, the downstream contributions to South and East Asia from MERRA-2 are only 0.36 and 0.84 times that of CALIOP, respectively. This difference implies the overestimation of the wet and dry depositions of the model, especially in the low latitude zone. The quantification of the Central Asian dust transport allows a better understanding of the Central Asian dust cycle, and supports the calibration/validation of aerosol-related modules of regional and global climate models. [ABSTRACT FROM AUTHOR]

The need for monitoring Asian dust is increasing owing to concerns about its harmful effects on ecosystems and human health. Strontium isotope ratios of mosses can be used to monitor Asian dust because of the traceability of these ratios and nutrient uptake by mosses from atmospheric deposition. Hence, the present study examined the suitability of strontium isotope ratios of mosses for monitoring Asian dust. Given the higher strontium isotope ratios of Asian dust than those of domestic origins, these ratios of mosses would be higher in areas with Asian dust. Moss samples were collected from 13 sites across Japan. The strontium isotope ratios of mosses in all study sites were lower than those of Asian dust. Although western Japan is more strongly influenced by Asian dust than eastern Japan, there were no significant differences in the strontium isotope ratios between these regions. Notably, the strontium isotope ratios of mosses significantly and positively correlated with those of the local soil across the study sites. These results indicate that strontium in mosses was derived from the local soil, and this uptake pattern may be attributed to a considerable supply of soil-derived strontium. In conclusion, the strontium isotope ratio of mosses is not a suitable indicator for the influence of Asian dust in Japan. Future studies should investigate whether these results could be applied to epiphytic mosses as potential indicators for Asian dust because epiphytes are less influenced by soil-derived minerals than terrestrial mosses. [ABSTRACT FROM AUTHOR]

As the second-largest shifting sand desert worldwide, the Taklimakan Desert (TD) represents the typical aeolian landforms in arid regions as an important source of global dust aerosols. It directly affects the ecological environment and human health across East Asia. Thus, establishing a comprehensive environment and climate observation network for field research in the TD region is essential to improve our understanding of the desert meteorology and environment, assess its impact, mitigate potential environmental issues, and promote sustainable development. With a nearly 20-yr effort under the extremely harsh conditions of the TD, the Desert Environment and Climate Observation Network (DECON) has been established completely covering the TD region. The core of DECON is the Tazhong station in the hinterland of the TD. Moreover, the network also includes 4 satellite stations located along the edge of the TD for synergistic observations, and 18 automatic weather stations interspersed between them. Thus, DECON marks a new chapter of environmental and meteorological observation capabilities over the TD, including dust storms, dust emission and transport mechanisms, desert land–atmosphere interactions, desert boundary layer structure, ground calibration for remote sensing monitoring, and desert carbon sinks. In addition, DECON promotes cooperation and communication within the research community in the field of desert environments and climate, which promotes a better understanding of the status and role of desert ecosystems. Finally, DECON is expected to provide the basic support necessary for coordinated environmental and meteorological monitoring and mitigation, joint construction of ecologically friendly communities, and sustainable development of central Asia. [ABSTRACT FROM AUTHOR]

Long-range transport of North African and Middle Eastern dust has been frequently observed in East Asia. However, understanding of their characteristics and effects in this region is insufficient. In this study, the transboundary transport of multi-source dust was captured by a polarized micro-pulse lidar from April 5 to 10, 2012, during a field campaign in Dunhuang, northwest China. Six dust plumes (DN1-DN6) were selected based on the spatiotemporal evolution of the depolarization ratio. Furthermore, the source, vertical characteristics of the coarse and fine components and their contributions were investigated by combining lidar observation with the WRF-Chem model simulation. The results indicated that DN1 was from Central Asia and it took approximately 4–5 days. DN2 originated from sources in North Africa and the Middle East and took approximately 6–7 days to reach Dunhuang. Samples DN3-DN6 originated from the Taklimakan and Gobi deserts in East Asia. A noticeable contrast was observed in the vertical distribution of the coarse and fine components between the long-range transported (DN1∼DN2) and fresh (DN3∼DN6) dust plumes. DN1 and DN2 presented comparable dust components (DD = Dc + Df, where Dc and Df are coarse- and fine-mode dust, respectively) and non-dust (ND) component contributions and a high predominance of Dc particles was present with at least 40% of total components in DN3-DN4. The contribution of ND particles was nearly negligible in DN5 and DN6. Lidar observations and model simulation both indicated that the maximum contribution of North African and Middle Eastern dust to the local aerosol loading exceeded 58%. However, the model simulation underestimated the contribution of DN1 by an average of 18% compared to lidar observations because DN1 was not reproduced well. This implies that the vertical distribution of dust should be carefully considered when dust impacts (e.g., radiation effects and air quality) are finely assessed using a model on a regional scale. [Display omitted] • POLIPHON algorithm was conducted to the P-MPL observations over northwest China. • A noticeable contrast exists in the vertical structure between the long-range transported and fresh dust plumes. • Model underestimates the contribution of long-range transported dust to local aerosol loading. [ABSTRACT FROM AUTHOR]

Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10 -2 to 10 2 L -1 in dust events at temperatures between -25 and -5 ∘ C. The average contributions of heat-sensitive INPs at three temperatures, -10 , -15 , and -20 ∘ C, were 81±12 %, 70±15 %, and 38±21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (-35 to -6 ∘ C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models. [ABSTRACT FROM AUTHOR]

The Cloud-Aerosol Transport System (CATS) lidar, on board the International Space Station (ISS), provides a new opportunity for studying aerosol vertical distributions, especially the diurnal variations, from space observations. In this study, we investigate the seasonal variations and diurnal cycles in the vertical aerosol extinction coefficients (AECs) over East Asia by taking advantage of 32 months of continuous and uniform aerosol measurements from the CATS lidar. Over the Tibetan Plateau, a belt of AECs at approximately 6 km between 30 and 38 ∘ N persistently exists in all seasons with an obvious seasonal variation. In summer, the aerosols at 6 km are identified as a mixture of both anthropogenic aerosols transported from India and coarse dust particles from Asian dust sources. In addition, the high AECs up to 8 km in summer over the Tibetan Plateau are caused by smoke aerosols from thermal dynamic processes. In fall and winter, the northern slope of the plateau is continuously influenced by both dust aerosols and polluted aerosols transported upslope from cities located at lower elevations in northwestern Asia. The diurnal variation in AECs in North China is mainly related to the diurnal variations in the transported dust and local polluted aerosols. Below 2 km , the AEC profiles in North China at 06:00 and 12:00 CST (China standard time) are significantly higher than those at 00:00 and 18:00 CST, reaching a maximum at midday. The aerosol vertical profiles over the Tarim Desert region in summer have obvious diurnal variations, and the AECs at 12:00 and 18:00 CST are significantly higher than those at 00:00 and 06:00 CST, which are induced by the strong diurnal variations in near-surface wind speeds. In addition, the peak in the AEC profiles has a significant seasonal variation, which is mainly determined by the boundary layer height. [ABSTRACT FROM AUTHOR]

The Taklamakan desert is an important dust source for the global atmospheric dust budget and a cause of the dust weather in East Asia. The characterization of Taklamakan dust in the source region is still very limited. To fill this gap, the DAO (dust aerosol observation) was conducted in April 2019 in Kashi, China. The Kashi site is about 150 km from the western rim of the Taklamakan desert and is strongly impacted by desert dust aerosols, especially in spring time, i.e., April and May. According to sun–sky photometer measurements, the aerosol optical depth (at 500 nm) varied in the range of 0.07–4.70, and the Ångström exponent (between 440 and 870 nm) in the range of 0.0–0.8 in April 2019. In this study, we provide the first profiling of the 2α+3β+3δ parameters of Taklamakan dust based on a multiwavelength Mie–Raman polarization lidar. For Taklamakan dust, the Ångström exponent related to the extinction coefficient (EAE, between 355 and 532 nm) is about 0.01 ± 0.30, and the lidar ratio is found to be 45 ± 7 sr (51 ± 8–56 ± 8 sr) at 532 (355) nm. The particle linear depolarization ratios (PLDRs) are about 0.28–0.32 ± 0.07 at 355 nm, 0.36 ± 0.05 at 532 nm and 0.31 ± 0.05 at 1064 nm. Both lidar ratios and depolarization ratios are higher than the typical values of Central Asian dust in the literature. The difference is probably linked to the fact that observations in the DAO campaign were collected close to the dust source; therefore, there is a large fraction of coarse-mode and giant particles (radius >20 µ m) in the Taklamakan dust. Apart from dust, fine particles coming from local anthropogenic emissions and long-range transported aerosols are also non-negligible aerosol components. The signatures of pollution emerge when dust concentration decreases. The polluted dust (defined by PLDR 532≤0.30 and EAE 355-532≥0.20) is featured with reduced PLDRs and enhanced EAE 355-532 compared to Taklamakan dust. The mean PLDRs of polluted dust generally distributed in the range of 0.20–0.30. Due to the complexity of the nature of the involved pollutants and their mixing state with dust, the lidar ratios exhibit larger variabilities compared to those of dust. The study provides the first reference of novel characteristics of Taklamakan dust measured by Mie–Raman polarization lidar. The data could contribute to complementing the dust model and improving the accuracy of climate modeling. [ABSTRACT FROM AUTHOR]

Emission inventories of anthropogenic transition metals, which contribute to aerosol oxidative potential (OP), in Asia (Δx = 0.25°, monthly, 2000–2008) and Japan (Δx = 2 km, hourly, mainly 2012) were developed, based on bottom‐up inventories of particulate matters and metal profiles in a speciation database for particulate matters. The new inventories are named Transition Metal Inventory (TMI)‐Asia v1.0 and TMI‐Japan v1.0, respectively. It includes 10 transition metals in PM2.5 and PM10, which contributed to OP based on reagent experiments, namely, Cu, Mn, Co, V, Ni, Pb, Fe, Zn, Cd, and Cr. The contributions of sectors in the transition metals emission in Japan were also investigated. Road brakes and iron‐steel industry are primary sources, followed by other metal industry, navigation, incineration, power plants, and railway. In order to validate the emission inventory, eight elements such as Cu, Mn, V, Ni, Pb, Fe, Zn, and Cr in anthropogenic dust and those in mineral dust were simulated over East Asia and Japan with Δx = 30 km and Δx = 5 km domains, respectively, and compared against the nation‐wide seasonal observations of PM2.5 elements in Japan and the long‐term continuous observations of total suspended particles (TSPs) at Yonago, Japan in 2013. Most of the simulated elements generally agreed with the observations, while Cu and Pb were significantly overestimated. This is the first comprehensive study on the development and evaluation of emission inventory of OP active elements, but further improvement is needed. Plain Language Summary: Aerosol oxidative potential (OP) has been focused on as a better health hazard of aerosols than PM2.5. OP is quantified by in vitro assays to mimic the in vivo generation of superoxide radicals to cause oxidative stress on human cells. OP has been reported to be more strongly associated with cardiorespiratory outcomes than PM2.5. Transition metals ions, organics, and elementary carbon, together with their interactions, have been reported as important compounds, but the relative magnitudes of contributions to total OP have not yet been fully understood. In this study, as a first step, we developed emission inventories and a numerical model to predict OP active transition metals in Asia and Japan and compared them with observations. We also quantitatively derived the major emission sources for the important metals such as Cu, Mn, Fe, V, and Ni in Japan. The current study is the first step toward better predicting the health hazard of aerosols. As the next step in the future, water solubility of metals and OP active organics, together with their interactions, should be considered. Key Points: Emission inventories of transition metals, which contribute to aerosol oxidative potential (OP), in Asia and Japan were developedMost of simulated elements (Mn, V, Ni, Fe, Zn, and Cr) agreed with observation, while Cu and Pb were significantly overestimatedRoad brakes and iron‐steel industry are primary sources, followed by metal industry, navigation, incineration, power plants, and railway [ABSTRACT FROM AUTHOR]

Mineral dust particles play an important role in the Earth system, imposing a variety of effects on air quality, climate, human health, and economy. Accurate forecasts of dust events are highly desirable to provide an early warning and inform the decision-making process. East Asia is one of the largest dust sources in the world. This study applies and evaluates four widely used regional air quality models to simulate dust storms in northeastern China. Three dust schemes in the Weather Research and Forecasting model with Chemistry (WRF-Chem) (version 3.9.1), two schemes in both CHIMERE (version 2017r4) and CMAQ (version 5.2.1), and one scheme in CAMx (version 6.50) were applied to a dust event during 4–6 May 2015 in northeastern China. Most of these models were able to capture this dust event with the exception of CAMx, which has no dust source map covering the study area; hence, another dust source mask map was introduced to replace the default one for the subsequent simulation. Although these models reproduced the spatial pattern of the dust plume, there were large discrepancies between predicted and observed PM 10 concentrations in each model. In general, CHIMERE had relatively better performance among all simulations with default configurations. After parameter tuning, WRF-Chem with the Air Force Weather Agency (AFWA) scheme using a seasonal dust source map from Ginoux et al. (2012) showed the best performance, followed by WRF-Chem with the UOC_Shao2004 scheme, CHIMERE, and CMAQ. The performance of CAMx had significantly improved by substituting the default dust map and removing the friction velocity limitation. This study suggested that the dust source maps should be carefully selected on a regional scale or replaced with a new one constructed with local data. Moreover, further study and measurement of sandblasting efficiency of different soil types and locations should be conducted to improve the accuracy of estimated vertical dust fluxes in air quality models. [ABSTRACT FROM AUTHOR]

Dust heterogeneous chemistry plays an important role in the atmosphere and has significant effects on climate and the environment. However, the traditional modelling method treats heterogeneous chemistry as pseudo-first-order reactions, which retains significant uncertainties, hindering the accurate prediction of secondary inorganic aerosols. In contrast, the actual dust heterogeneous chemistry involves complex multiphase reactions, including partition between gas- and dust-phase, and reactions on the dust surface. In this study, we implement a photocatalytic mechanism into the GEOS-Chem model and apply it to investigate the impact on atmospheric chemistry during a dust storm over East Asia during April 9–14th, 2018.With the photocatalytic heterogeneous chemistry (PHO), model simulation better reproduces observed sulfate and nitrate concentrations than those with the traditional pseudo-first-order mechanism (TDT) or without any dust heterogeneous chemistry at all (BASE). As validated against observations, normalized mean bias (NMB) in PHO reduces substantially compared to TDT, from −61.65% and 103.38% to −2.19% and 6.83% at Nanjing and Shanghai, respectively. The model also accurately simulates gaseous precursors such as SO 2 and NO 2, as evidenced by a decline in NMB from 103.38% to 81.80%–6.83% and 6.64% at the two sites, respectively. Furthermore, our analysis indicates that the larger dry deposition velocity of dust-phase sulfate and higher sulfate concentrations simulated by PHO jointly lead to a significant increase in SO 4 dry deposition flux, demonstrating that the dust heterogeneous chemical process facilitates the removal of aerosol pollutants during dust events. These findings reinforce the need for enhancing the representation of dust heterogeneous chemistry in atmospheric models, underlining the criticality of this factor in accurate predictive modelling and environmental impact studies. • Implementing a dust photocatalytic mechanism in the GEOS-Chem model instead of the traditional method. • Using dust photocatalytic mechanism, model better reproduces observed SO 4 and NIT concentrations than the traditional. • Gas-particle conversion in dust heterogeneous chemistry facilitates removal of aerosol pollutants during the dusty period. [ABSTRACT FROM AUTHOR]

This study proposes an aerosol-type classification based on the particle linear depolarization ratio (PLDR) and single-scattering albedo (SSA) provided in the AErosol RObotic NETwork (AERONET) version 3 level 2.0 inversion product. We compare our aerosol-type classification with an earlier method that uses fine-mode fraction (FMF) and SSA. Our new method allows for a refined classification of mineral dust that occurs as a mixture with other absorbing aerosols: pure dust (PD), dust-dominated mixed plume (DDM), and pollutant-dominated mixed plume (PDM). We test the aerosol classification at AERONET sites in East Asia that are frequently affected by mixtures of Asian dust and biomass-burning smoke or anthropogenic pollution. We find that East Asia is strongly affected by pollution particles with high occurrence frequencies of 50 % to 67 %. The distribution and types of pollution particles vary with location and season. The frequency of PD and dusty aerosol mixture (DDM+PDM) is slightly lower (34 % to 49 %) than pollution-dominated mixtures. Pure dust particles have been detected in only 1 % of observations. This suggests that East Asian dust plumes generally exist in a mixture with pollution aerosols rather than in pure form. In this study, we have also considered data from selected AERONET sites that are representative of anthropogenic pollution, biomass-burning smoke, and mineral dust. We find that average aerosol properties obtained for aerosol types in our PLDR–SSA-based classification agree reasonably well with those obtained at AERONET sites representative for different aerosol types. [ABSTRACT FROM AUTHOR]

This study proposes an aerosol-type classification based on the particle linear depolarization ratio (PLDR) and single scattering albedo (SSA) provided in the AErosol RObotic NETwork (AERONET) version 3 level 2.0 inversion product. We compare our aerosol-type classification with an earlier method that uses fine-mode fraction (FMF) and SSA. Our new method allows for a refined classification of mineral dust that occurs as a mixture with other absorbing aerosols: pure dust (PD), dust-dominated mixed plume (DDM), and pollutant-dominated mixed plume (PDM). We test the aerosol classification at AERONET sites in East Asia that are frequently affected by mixtures of Asian dust and biomass-burning smoke or anthropogenic pollution. We find that East Asia is strongly affected by pollution particles with high occurrence frequencies of 50% to 67%. The distribution and types of pollution particles vary with location and season. The frequency of PD and dusty aerosol mixture (DDM+PDM) is slightly lower (34% to 49%) than pollution-dominated mixtures. Pure dust particles have been detected in only 1% of observations. This suggests that East Asian dust plumes generally exist in a mixture with pollution aerosols rather than in pure form. In this study, we have also considered data from selected AERONET sites that are representative of anthropogenic pollution, biomass-burning smoke, and mineral dust. We find that average aerosol properties obtained for aerosol types in our PLDR-SSA-based classification agree reasonably well with those obtained at AERONET sites representative for different aerosol types. [ABSTRACT FROM AUTHOR]

Mineral dust particles play an important role in the Earth system, imposing a variety of effects on air quality, climate, human health, and economy. Accurate forecasts of dust events are highly desirable to provide early-warning and inform decision-making. East Asia is one of the largest dust sources in the world. This study applies and evaluates four widely used regional air quality models to simulate dust storms in East Asia. Three dust schemes in the Weather Research and Forecast with Chemistry (WRF-Chem) (version 3.9.1), two schemes in CHIMERE (version 2017r4) and CMAQ (version 5.2), and one scheme in CAMx (version 6.50), were applied to a dust event during May 4th~6th, 2015 in Northeastern China. Most of these models were able to capture this dust event, except CAMx which has no dust source map covering the study area, hence is excluded from subsequent analysis. Although these models reproduced the spatial pattern of the dust plume, there were large discrepancies between predicted and observed PM10 concentrations in each model. In general, CHIMERE had relatively better performance among all simulations with default configurations. After parameter tuning, WRF-Chem with the AFWA scheme using seasonal dust source map from Ginoux et al. (2012) showed the best performance, followed by WRF-Chem with UOC_Shao2011 scheme, CHIMERE, and CMAQ. This study suggested that the dust source maps should be carefully selected or replaced with a new one constructed with local data. Moreover, further study and measurement on sandblasting efficiency of different soil types and locations should be conducted to improve the accuracy of estimated vertical dust flux in air quality models. [ABSTRACT FROM AUTHOR]

In the process of dust transport, the Tibetan Plateau (TP) plays a significant role because of its high topography. A dust event occurred from 2 to 5 April 2018 was chosen to study the role of TP in middle troposphere using Weather Research and Forecasting Model coupled with chemistry (WRF-Chem) model. The model reproduced the meteorological parameters, spatiotemporal distribution of dust reasonably. This study found that the dust originated from Taklimakan Desert (TD) was rose to 7 km under the influence of strong updraft flow and dust elevated heat pump, then transported eastward under the guidance of flat westerly flow. Subsequently, a trough passing the TD region carried the raised dust southward to the TP, leading to a thick dust belt with the concentration >200 μg m−3 suspended over the TP. After that, the dust are entrained to upper troposphere by the TP and then continue to transport eastward to the northeast of East Asia (NE). The TP acted as a transit station that lifted dust aerosol to the upper level. Moreover, the cold vortex over Siberia was stronger compared with the climatologic mean value. Consequently, cold air separated from the vortex enhanced the East Asian trough and triggered the dust emission. The above anomaly was conducive to the TD-TP-NE transport of dust. The dust-induced heating rate over NE peaked at 1.0 K/day at 7.5 km, which was comparable to TP. The dust layer over NE may further affect atmospheric circulation, clouds properties and precipitation. • Two pathways for the transport of dust aerosol from Taklimakan Desert (TD) to northeast of East Asia (NE) are identified. • The Tibetan Plateau (TP) acts as a dust transit station in middle troposphere. • Strong cold vortex are responsible for dust emission and the TD-TP-NE tranport path of dust. [ABSTRACT FROM AUTHOR]

The snow-darkening forcing of dust (SFD) is known to occur when dust-covered snow reduces surface albedo and absorbs more radiation, which causes snowmelt and surface warming. To date, few studies have focused on how SFD affects atmospheric circulation. In this study, we used a climate model to evaluate the influence of the SFD on seasonal changes in coupled monsoon westerlies over East Asia. The results indicate that the SFD causes anomalies in temperature, precipitation, and atmospheric circulation over East Asia. In December and January (DJ), the temperature increase over the Tibetan Plateau is significant, and the anomalous anticyclonic circulation causes a weakening of the westerly circulation during this period. In February, March, and April (FMA), the SFD causes an increase in temperature over the plateau and its eastern flank and widespread anomalous cooling to the north, which can be attributed to diabatic cooling of the upper atmosphere. These changes in thermal conditions lead to enhanced westerly winds and weakened East Asian winter monsoons during FMA. The enhanced westerly winds bring more precipitation to the East Asian continent. In May, June, and July (MJJ), only the Tibetan Plateau is significantly warmed in East Asia. At this time, the westerly circulation weakens, and the East Asian summer monsoon strengthens. The low-level atmospheric circulation shows anomalous westerly winds over South Asia. The anomalous westerly winds from Central Asia bring dry air and result in reduced precipitation over India. • The snow-darkening effect of dust (SFD) on the East Asian monsoon and westerlies are different among seasons. • The SFD leads to weaker westerly winds and winter monsoon in December–January. • The SFD leads to weaker westerly winds and stronger summer monsoon in May–July. [ABSTRACT FROM AUTHOR]

The distributions and radiative effects of mineral dust during winter half year over East Asia have been investigated in this study. The mineral dust is mainly located around 40°N, however, the aerosol optical depth (AOD) of dust can exceed over 0.6 over the Taklimakan desert both in MODIS observations and model simulations. The direct radiative forcings (DRFs) of dust are about -9.23 W m -2 at the surface and 0.39 W m -2 at the top of atmosphere (TOA) in winter half year. With the presence of an interactive ocean model, the dust will decrease surface air temperature over East Asia (-0.25 K) except for oceanic regions. The increase in atmospheric temperature (0.015 K) will weaken the total heat flux and affect air specific humidity, which will finally decrease the precipitation over East Asia (-0.06 mm day -1 ). Sea surface temperature (SST) responses are very important when evaluating the climatic effects of dust over East Asia. If we fix the SST in regional model, the weakening trend of precipitation can reach up to -0.08 mm day -1 . [ABSTRACT FROM AUTHOR]

Mixing of Asian mineral dust with anthropogenic pollutants allows pollutants (e.g. sulfate and nitrate) to be transported over longer distances (e.g. to the northern Pacific, even to North America) along with dust particles. This mixing therefore affects the atmospheric and oceanic environment at local, regional and even continental scales. In this study, we used a three-dimensional regional chemical transport model (Nested Air Quality Predicting Modeling System, NAQPMS) to examine the degree of mixing between Asian mineral dust and anthropogenic pollutants in a superduststorm event during 19-22 March 2010. Influences of the mixing processes on regional atmospheric environmental and oceanic biogeochemical cycles were also investigated. A comparison with measurements showed that the model reproduced well the trajectory of long-range dust transport, the vertical dust profile, the chemical evolution of dust particles. We found that along-path mixing processes during the long-range transport of Asian dust led to increasingly polluted particles. As a result, ~60% of the sulfate and 7095 % of the nitrate in the downwind regions was derived from active mixing processes of minerals with pollutants sourced from the North China Plain and enhanced by transport over South China. This mixing had a significant impact on the regional-scale atmospheric composition and oceanic biogeochemical cycle. Surface HNO, SO2 and O3 were decreased by up to 90%, 40% and 30%, respectively, due to the heterogeneous reactions on dust particles. Fe solubility rose from ~0.5% in the Gobi region to ~3-5% in the northwestern Pacific, resulting from oxidization of SO2 on dust particles. Total Fe(II) deposition in the ocean region of East Asia reached 327 tons during the 4-day dust event, created a calculated primary productivity of ~520 mgC m-2 d-1 in the Kuril Islands, which can support almost 100% of the observed mean marine primary productivity in spring in this region (526 mgC m-2 d-1). [ABSTRACT FROM AUTHOR]

Mineral dust from the deserts and arid areas in East Asia plays a critical role in regional climate and air quality. Based on integrated satellite observations and MERRA-2 reanalysis, we provide an observational insight into dust activities governing spatial patterns of dust aerosols over East Asia. With Moderate resolution Imaging Spectroradiometer Aerosol Optical Depth (AOD) and Ozone Monitoring Ultraviolet Aerosol Index (UVAI), fixed dust-active areas with distinct spatial-temporal differences are revealed. Besides the few dust storms mostly in spring, unnoticeable but frequent dust plumes are found to be the predominant sources of prevailing dust particles over East Asia. Compared with the active dust sources in Taklimakan Desert throughout the year, dust activities in Gobi deserts are at a much lower frequency. The elevated dust plumes are concentrated within 2–6 km over the deserts with large seasonal variations, and can be transported downstream to eastern China and Sichuan Basin within 3–5 days. Moreover, owing to the lack of enough strong winds, these dust plumes tend to be concentrated above the haze layers near surface in eastern China. The intense temperature inversion during winter and early spring can delay the mixing of dust-pollution. Despite a generally reasonable performance in dust AOD, MERRA-2 reanalysis exhibits some uncertainties in reproducing spatial locations of dust hotspots, dust concentration, and transport process. Our results emphasize significant role of the inapparent but prevalent dust plumes in air quality and in climate effects of East Asia. • Inapparent but frequent dust plumes are the predominant sources of prevalent dust aerosols over East Asia. • Dust plumes tend to overlay over anthropogenic pollution near surface with a delaying dust-pollution mixing. • MERRA-2 underestimates the dust loading in Taklimakan Desert and overestimates in Gobi deserts. [ABSTRACT FROM AUTHOR]

Mineral dust is an important player in global air quality and climate, but little is known about its variability and trends under the simultaneous influence of climate and land cover changes, particularly in East Asia where intense land cover change has occurred in recent decades. Here we determined the interannual variability and trends in dust emission from the main East Asian dust sources and examined to what extent these variations and trends were driven by climatic or land cover changes. We first optimized the dust emission module in the GEOS-Chem chemical transport model with better representation of dust physics and dependence on vegetation and wind variability. We then conducted simulations to quantify the impacts of climate and land cover variability and trends on springtime dust emission over 1982–2010 from the Teklimakan Desert, Gobi Desert and the whole East Asian desert domain. We found that dust emission from Gobi decreased substantially from the 1980s to 1990s, and then slightly increased toward the 2000s, leading to an overall reduction by 35% over the whole period. These changes were predominantly driven by meteorological changes and the effects of land cover change were negligible. Dust emission from Teklimakan increased from the 1980s to 1990s, but decreased afterward, leading to an overall reduction by 20%, albeit with large interannual variability. The overall trend was attributable to a consistent reduction in dust emission due to enhanced vegetation density in the periphery of the desert, accompanied by larger but more varying changes due to meteorological factors. Time series comparison and regression analysis indicated that in both deserts (especially Gobi), surface wind speed, followed by total precipitation, was the most important meteorological factor controlling dust variability and trends, with the weakening of wind playing the largest role in the overall decline in dust emission over the whole period. Overall, the interannual variability and trends of East Asian dust emission are largely shaped by climatic factors, with the land cover playing secondary but locally important roles, especially in the semiarid and non-desert regions undergoing rapid land cover change and desertification. • Dust emission in Gobi significantly decreased due to meteorological changes. • There were no significant trends for dust emission in Teklimakan. • Dust emission changes were controlled predominantly by climate variability. • Land cover change was regionally important for dust changes in Teklimakan. • Wind and precipitation were dominant drivers for dust emission variability. [ABSTRACT FROM AUTHOR]

Wind-blown dust plays a crucial role in air quality, biogeochemical cycles, and climate change. In East Asia, one of the main dust source regions in the world, dust storms frequently engulf eastern China, with a substantial negative effect on air pollution and the ecological environment. By integrating multiple observations and the online coupled meteorology-chemistry model WRF-Chem, a severe dust storm event originating from the Gobi Desert in early May 2017 is comprehensively analyzed from the perspective of emission estimation, meteorological feedback, and the possible impact on the ecological environment. We optimize the size distribution of dust aerosol by applying local observations to better represent dust emission and regional transport in the model. Both the observations and simulations indicate that the dust storm broke out with PM 10 concentrations exceeding 1500 μg/m3 in the source region of the Gobi Desert, and was quickly transported downwind, deteriorating the air quality of cities in northern and eastern China. Moreover, we find that the dust storm significantly perturbed the temperature stratification, since mineral dust is a radiatively active aerosol and can absorb both short- and long-wave radiation. The upper dust layer at an altitude of around 2–3 km became warmer by 1–2 °C while the surface temperature decreased by about 2 °C, making the planetary boundary layer more stable and indirectly aggravating local air pollution near the ground in eastern China. Furthermore, during this event, a large amount of dust deposition increased ocean primary productivity, with the maximum Chlorophyll-a concentration rising from 4 to 14 mg/m3 in the central area of the Yellow Sea. This study highlights the critical impact of Asian dust pollution on air quality and marine ecosystems in downwind areas. • Modified WRF-Chem dust particle size distribution significantly improved the simulation ability of dust. • Multiple observations combined with model results to analyse dust episode comprehensively. • Dust aerosol makes the upper layer warm and the lower layer cool, increasing the stability of the boundary layer. • Dust deposited into the ocean is significantly associated with phytoplankton blooms. [ABSTRACT FROM AUTHOR]

Particles larger than 5.0 μm in diameter are important to keep the size distribution for mineral dust but it is difficult to represent them in numerical models due to the complex emission process and quick gravitational deposition. To improve this situation, the cumulative distribution function of the Weibull distribution is used to represent the instant wind larger than the model grid-mean wind speeds of the sectional dust forecast model, China Meteorological Administration Unified Atmospheric Chemistry Environment/Dust (CUACE/Dust). Size distributions for dessert soil texture in China and mass median diameters for the three lognormal populations of dust flux released are also improved from observations in Asian source areas. With all these updating, the mass size distribution of dust flux from the model is much closer to the observed value, which changes the original unreasonable single-peak distribution, coming close to the distribution trend with increasing particle size bins. It then improves the emission for coarse particles larger than 10.0 μm in source areas. Moreover, both the varied values and changing shape patterns of column volume particle size distributions simulated in the downwind areas compatible to the observed by the global AErosol RObotic NETwork (AERONET) achieving an obvious improvement for the size distribution of coarse particles larger than 5.0 μm in these downwind areas. • The sectional dust production scheme is adapted to the model spatial scales with a cumulative Weibull distribution function. • New soil texture in China and mass medium diameters in Asian source areas has been deduced from observations. • Reasonable dynamic mass size distributions have been achieved both in the source areas and downwind areas. [ABSTRACT FROM AUTHOR]

Although variations of atmospheric dust aerosols emitted from different sources within Asia have been studied separately in previous research, the characteristics and causes of these changes have not been fully explored. This study used the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) data set for 1980–2016 to compare seasonal and interannual variations of atmospheric dust aerosols between mid- and low-latitude sources of Asia and explore the reasons for these variations. The seasonal variation of atmospheric dust aerosols in mid-latitude sources was different from that of low-latitude sources. The column burden of dust aerosols in the mid-latitude sources (including East and Central Asia) reached their maximum in spring, and accounted for about 37% and 33% of their annual total load, respectively. The maximum dust aerosols in spring in the Central Asia sources resulted from multiple factors such as soil wetness, snow depth, and vertical wind shear, but they were negatively correlated with soil wetness on the interannual scale (r = −0.65). The maximum dust aerosol burden in spring in the East Asia sources resulted from vertical wind shear in the lower troposphere, and showed a positive correlation with the interannual change of dust aerosols in this source region (r = 0.51). However, the column burden of dust aerosols in the low-latitude sources (including South and West Asia) reached their maximum in summer, and accounted for about 41% and 37% of their annual total load, respectively. The maximum dust aerosols of summer in the low-latitude sources also resulted from vertical wind shear in the lower troposphere with correlation coefficients of 0.50 and 0.73 in the South and West Asia sources, respectively. The present results may help in further understanding the formation and change of Asian dust aerosols. • The dust aerosols in the mid-latitude sources including East and Central Asia reached their maximum in spring. • The dust aerosols in the low-latitude sources including South and West Asia reached their maximum in summer. • The maximum dust aerosols in spring in the East Asia sources resulted from vertical wind shear. • The maximum dust aerosols in spring in the Central Asia sources resulted from soil wetness, snow, and vertical wind shear. • The maximum dust aerosols of summer in the low-latitude sources resulted from vertical wind shear. [ABSTRACT FROM AUTHOR]

Absorption aerosol optical depth induced by black carbon (AAODBC) was retrieved using the depolarization ratio and single scattering albedo provided by the Aerosol Robotic Network (AERONET) inversion products over East Asia. Our analysis considered AERONET data from six sites in East Asia that are mostly affected by anthropogenic pollution, black carbon (BC) emissions, and natural mineral dust, during the period 2001–2018. We identified a rapid reduction in total aerosol optical depth (AODT) of −0.0106 yr−1 over Beijing, whereas no considerable trend was observed at the Korean and Japanese sites. The long-term data for AAODBC showed decreasing trends at all sites. We conclude that successful emission control policies were the major underlying driver of AODT and AAODBC reductions over East Asia, particularly in China, during the study period. Values of the AAODBC/AODT ratio revealed that, although these policies were successful, the Chinese government needs to undertake stricter measures toward reducing BC emissions. We found that AAODBC follows seasonal trends, peaking in the colder months. This suggests that in East Asia, particularly in China, domestic coal burning is still of concern. [ABSTRACT FROM AUTHOR]

In this paper, a 20-year (1991–2010) simulation of dust aerosol emission is conducted by using the global climate model CAM 5.1 (Community Atmosphere Model, version 5.1). The simulation results revealed that North Africa, the Arabian Peninsula and the Middle East, East Asia, Australia, and the other regions respectively account for 60%, 18%, 12%, 2.5% and 7.5% of the global dust aerosol emission. On this basis, the climatology of dust aerosol emission, deposition and transport in the major dust source regions of the world are characterized. The results show that the inter-annual trends of dust emissions and depositions in the four major source areas are basically consistent, and the seasonal variations of dust emissions, dry and wet depositions are stronger than inter-annual variations. The seasonal variations of emissions and total depositions are the strongest in East Asia and the weakest in North Africa. The strongest seasonal variation of wet deposition appears in North Africa and the weakest in Australia. The dry and wet deposition ratios vary significantly with season. East Asia is dominated by wet deposition, while other areas are dominated by dry deposition. The dust transport in four major dust regions is mainly affected by the circulation systems at each level, the free tropospheric (500 hPa) transport of dust aerosol is controlled by the mid-latitude westerlies, and the dust aerosol is predominantly transported from west to east. But, the transport of dust aerosols in the atmospheric boundary layer shows distinct regional characteristics, with weak inter-annual variation and strong seasonal variation. • A 20-year (1991–2010) simulation of dust aerosol is conducted by using the global climate model CAM 5.1. • The simulation results revealed that North Africa, the Arabian Peninsula and the Middle East, East Asia, Australia are four major dust source regions, the climatology of dust aerosol emission, deposition and transport in the major dust source regions of the world are characterized. • The dust transport in four major dust regions is mainly affected by the circulation systems at each level. [ABSTRACT FROM AUTHOR]

Aerosol plays an important role in the climate system by affecting the radiative and energy balances. Hence, in this paper, the spatial patterns of aerosol burden and aerosol optical properties (AOD) in four the Coupled Model Intercomparison Project phase 5 (CMIP5) models over East Asia during 2001–2005 are compared to quantify inter-model differences and to evaluate AOD simulations against observations. The evaluation of AOD against Moderate Resolution Imaging Spectroradiometer (MODIS) satellite retrievals shows that CMIP5 models can reproduce the spatial pattern of MODIS AOD reasonably well. The mean AOD over eastern China shows that NorESM1-M underestimates MODIS AOD by 40%, due to the lack of emissions of some aerosol components, such as nitrate, biogenic aerosol, and non-desert mineral dust. In contrast to that, CSIRO-Mk3.6.0 overestimates annual mean of MODIS AOD over eastern China by 20%, partially caused by larger aerosol emissions and burden. Compared to MODIS AOD, GFDL-CM3 performs the best in simulating AOD in eastern China, because ammonium and nitrate are included in this model. The comparisons of CMIP5 and Aerosol Robotic Network (AERONET) AOD show similar results. In addition, the simulated AOD values are closer to AERONET AOD in Mongolia, China, Japan and Korea than that in India. The results also reveal that there are some inter-model differences of aerosol burden over East Asia, caused by the inter-model differences of aerosol emissions, wet scavenging, and transport. Over eastern and northwestern China and the west Pacific, the inter-model differences of anthropogenic aerosol burden and spatial variabilities are smaller than that of natural aerosol burden. • The evaluation results show that CMIP5 models can reproduce the spatial pattern of MODIS AOD reasonably well. • Compared to MODIS AOD, GFDL-CM3 performs the best in simulating AOD in eastern China. • The simulated AOD values are closer to AERONET AOD in Mongolia, China, Japan and Korea than that in India. • The inter-model differences of aerosol burden are caused by aerosol emissions, wet scavenging, and transport. [ABSTRACT FROM AUTHOR]

• Homogenous reactive Fe isotope signatures revealed by acid leaching of Asian dust. • A first synthetic model on Fe release kinetics during acid leaching of particles. • Low δ56Fe found in reactive components of North Pacific pelagic sediments. Iron released from wind-blown dust has been widely suggested to be an important nutrient source for oceanic primary productivity. Once introduced into the seawater, the reactive Fe might get dissolved and impart its isotope signature into the water column. Characterization of the reactive iron isotope signatures of eolian dust will thus help to understand the budget of Fe in the global ocean. Yet, there are few systematic studies on the Fe isotope systematics of the dust sources across large spatial scale. Here, we report Fe isotope data from HCl leaching experiment on surficial samples from deserts and loess deposits of different locations spanning >3000 km spatially in east Asia, one of the most important dust source regions. Our data suggest most of the samples have relatively similar leaching signatures (δ56Fe = –0.09±0.07‰, n=9, 2 SD). To understand the kinetics of Fe release during proton promoted leaching of natural particles, a synthetic model taking into account of different dissolution dynamics of easily dissolvable Fe and silicate Fe was developed. The model was tested by continuous leaching of two representative pelagic sediment samples recovered from core LL44-GPC3 in the North Pacific. When introducing only one tunable parameter (i.e., the initial dissolution rate of Fe from hydro(oxides), with other parameters constrained by the dissolution kinetics), the model successfully reproduces leachate δ56Fe evolution and agrees reasonably well with Fe speciation in the studied marine sediment samples. We thus suggest that the leaching process can be well characterized by our kinetic model, while Fe isotopes in the initial leachates of the samples are dominated by endmember composition of the easily dissolvable Fe species. The small but distinct fractionation of Fe isotopes in the desert/loess samples from the parental upper continental silicate materials are suggested to record signatures of the secondary Fe species produced during weathering in the oxic environment. The significantly lighter Fe isotope compositions in the initial leachates of the North Pacific pelagic sediment samples compared to the east Asian desert/loess deposits indicate apparent isotope exchange of the dust reactive components with seawater dissolved species. The sedimentary light reactive Fe isotope signatures in turn point toward the contribution of sources characterized by low δ56Fe to the deep North Pacific and/or preferential uptake of 56Fe by seawater ligands from the dust reactive components particularly at the seawater-sediment interface. [ABSTRACT FROM AUTHOR]

Dust aerosol has important climate and environmental effects, which could be changed by internally mixing with anthropogenic aerosol as a result of heterogeneous reactions; however, the importance of these reactions is not fully understood yet. In this study, synergetic observations and an air quality model were used to analyze the transport of a severe dust storm and its impacts on nitrate and sulfate levels over East Asia between 3 and 11 May 2017. The model successfully reproduced the occurrence and transport of the dust storm compared to dust RGB imageries of the Himawari-8 satellite and dust extinction coefficients observed by LIDAR. The model also reasonably simulated the variations of observed nitrate and sulfate concentrations, and the results indicated that the dust heterogeneous reactions were dominant pathways for nitrate formation, but they had limited contribution for sulfate in both fine and coarse mode in Fukuoka, Japan. Dust nitrate formed rapidly after leaving China, and the highest period-averaged concentration of dust nitrate (>5 μg m−3) was shown over the Yellow Sea. Based on model results; we found that the mass ratio of dust nitrate to dust aerosol could reach 10% over the Pacific Ocean. Our results confirmed the importance of heterogeneous reactions on compositions of dust particles. [ABSTRACT FROM AUTHOR]

To determine the potential sources of dust at high latitudes in the Northern Hemisphere, this study measured the stable isotopic ratios of strontium (Sr), neodymium (Nd) and lead (Pb) in insoluble dust in snow samples (as well as in soil and sand samples) from sites in northwestern China and high latitudes in the Northern Hemisphere: Altay (Xinjiang, China), Ny-Ålesund (Svalbard), Barrow (Alaska) and the Arctic Ocean. The combined plots of the Sr–Nd–Pb isotopic data demonstrate that there are distinctive geographic patterns among the different sampling sites. The Sr–Nd results from the Altay (Xinjiang) and Ny-Ålesund (Svalbard) sites display overall crust-like isotopic patterns, indicating that local mineral sources represent a significant contribution. The 87Sr/86Sr and ε Nd (0) data from the sea ice snow samples from the Arctic Ocean and snow samples from Barrow (Alaska) suggest potential long-range dust transport to the Arctic region. Our results indicate that Russia may be a source of anthropogenic pollutants for the high Arctic region, while North America may be a source of anthropogenic pollutants for Barrow, Alaska. These findings are beneficial for protecting the environment at the global scale. Image 1 • New Sr–Nd–Pb data from Arctic and western Chinese snow samples are presented. • East Asian deserts are the primary dust source for the Arctic regions. • The anthropogenic pollutants in Arctic regions may be from Russia and North America. [ABSTRACT FROM AUTHOR]

We present the inversions (back-calculations or optimizations) of dust emissions for a severe winter dust event over East Asia in November 2016. The inversion system based on a fixed-lag ensemble Kalman smoother is newly implemented in the Weather Research and Forecasting model and is coupled with Chemistry (WRF-Chem). The assimilated observations are the hourly aerosol optical depths (AODs) from the next-generation geostationary satellite Himawari-8. The posterior total dust emissions (2.59 Tg) for this event are 3.8 times higher than the priori total dust emissions (0.68 Tg) during 25–27 November 2016. The net result is that the simulated aerosol horizontal and vertical distributions are both in better agreement with the assimilated Himawari-8 observations and independent observations from the ground-based AErosol RObotic NETwork (AERONET), the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). The developed emission inversion approach, combined with the geostationary satellite observations, can be very helpful for properly estimating the Asian dust emissions. [ABSTRACT FROM AUTHOR]

The input of aeolian mineral dust to the oceans is regarded as the major source in supplying bioavailable iron for phytoplankton growth. Severe dust events swept over East Asia during the 26 March to the 4 April 2018, decreasing air quality to hazardous levels, with maximum PM10 mass concentrations above 3000 μg m−3 in northern China. Based on a comprehensive approach that combines multiple satellite measurements, ground observations, and model simulation, we revealed that two severe Asian dust events originating from the Taklimakan and Gobi deserts on 26 March and 1 April, were transported through northern China and the East/Japan Sea, to the North Pacific Ocean by westerly wind systems. Transportation pathways dominated by mineral dust aerosols were observed at altitudes of 2–7 km in the source regions, and then ascending to 3–10 km in the North Pacific Ocean, with relatively denser dust plumes within the second dust episode than there were during the first. Our results suggest that mineral dust emitted from the Taklimakan and Gobi deserts could increase ocean primary productivity in the North Pacific Ocean by up to ~50%, compared to average conditions. This emphasizes the potential importance of the deposition of Asian mineral dust over the North Pacific Ocean for enhancing the biological pump. [ABSTRACT FROM AUTHOR]

Mineral dust interacts with radiation and cloud microphysics in East Asia can affect local and regional climate. In this study, we found that the occurrences of dust storms, blowing dust, and floating dust over northern China has decreased 76.7%, 68.5%, and 64.5% considerably since the beginning of this century. Based on a multi-dimensional ensemble empirical mode decomposition (MEEMD) method, a steady decrease in zonal maximum wind speed (up to -0.95 m/s) in the Northern Hemisphere was largely responsible for this recent decline in dust event occurrences. Then, a new detection technique that combines multi-satellite datasets with surface observations of dust events is developed to estimate the contribution of anthropogenic dust column burden from disturbed soils to the observed total dust. It is found that the percentage of the anthropogenic dust column burdens to total mineral dust is up to 76.8% by human activities during 2007-2014 in eastern China, but only less than 9.2% near desert source regions in northwestern China. However, we note that the anthropogenic effects on the dust loading for both regions are non-negligible. [ABSTRACT FROM AUTHOR]

The particle mixing state plays a significant yet poorly quantified role in aerosol radiativeforcing, especially for the mixing of dust (mineral absorbing) and anthropogenic pollution(black carbon absorbing) over East Asia. We have investigated the absorption enhancement ofmixed-type aerosols over East Asia by using the Aerosol Robotic Network observations andradiative transfer model calculations. The mixed-type aerosols exhibit significantly enhancedabsorbing ability than the corresponding unmixed dust and anthropogenic aerosols, asrevealed in the spectral behavior of absorbing aerosol optical depth, single scattering albedo,and imaginary refractive index. The aerosol radiative efficiencies for the dust, mixed-type,and anthropogenic aerosols are -101.1, -112.9, and -98.3 Wm−2τ−1 at the bottom of theatmosphere (BOA); -42.3, -22.5, and -39.8 Wm−2τ−1 at the top of the atmosphere(TOA); and 58.7, 90.3, and 58.5 Wm−2τ−1 in the atmosphere (ATM), respectively.The BOA cooling and ATM heating efficiencies of the mixed-type aerosols aresignificantly higher than those of the unmixed aerosol types over the East Asiaregion, resulting in atmospheric stabilization. In addition, the mixed-type aerosolscorrespond to a lower TOA cooling efficiency, indicating that the cooling effect bythe corresponding individual aerosol components is partially counteracted. Weconclude that the interaction between dust and anthropogenic pollution not onlyrepresents a viable aerosol formation pathway but also results in unfavorable dispersionconditions, both exacerbating the regional air pollution in East Asia. Our results highlightthe necessity to accurately account for the mixing state of aerosols in atmosphericmodels over East Asia in order to better understand the formation mechanism forregional air pollution and to assess its impacts on human health, weather, and climate. [ABSTRACT FROM AUTHOR]

Volcanic activity, including passive degassing and eruptive paroxysms, is one of the main sources of perturbation of the atmospheric composition. Among their different emissions, volcanoes are a source of gaseous and particulate sulphur. Sulphate aerosols, in particular, have the potential to interact with the radiative balance at different spatio-temporal scales. Observing sulphur compounds and sulphur-containing particles in a volcanic plume is a difficult task because a volcanic plume is a mix of different gaseous and particulate effluents, and because sulphur-containing gases and particles have similar spectral signatures [Sellitto and Legras, 2016]. For example, existing methods to retrieve volcanic sulphur dioxide (SO2) usually neglect the radiative impact of the subsequently formed Secondary Sulphate Aerosols (SSA) and vice-versa. To further investigate these possible interactions, in the first part of this study, we assess the combined sensitivity of simulated observations to the SO2 emissions and the subsequently formed SSA after idealized stratospheric and tropospheric eruptions. Three TIR satellite instruments are used as target observing systems: the Infrared Atmospheric Sounding Interferometer (IASI), the MODerate resolution Imaging Spectro radiometer (MODIS) and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI). The results of these sensitivity analyses show that the radiative interferences, produced by the simultaneous presence of SO2 and SSA on the outgoing TIR, is significant after few days from the eruption. In particular, neglecting SSA may bias SO2 retrievals [Guermazi et al., 2017]. Instrument with a high spectral resolution, like IASI, proved apt to retrieve SO2 and SSA total masses as independent quantities and with limited uncertainties [Guermazi et al., 2017]. In the second part of this contribution, we apply the outcomes of this sensitivity analysis to the retrieval of SSA from real IASI observations for the first time using the AEROIASI framework, used in the past to retrieve the mineral desert dust burden in 3D (Cuesta et al, 2015). We adapt this method for observing sulphate aerosols. This new scheme, AEROIASI-Sulphates is applied to selected eruptions of Mt Etna volcano. Results are presented and critically discussed.References:Cuesta, J., M. Eremenko, C. Flamant, G. Dufour, B. Laurent, G. Bergametti, M. Höpfner, J. Orphal, and D. Zhou (2015), Three‐dimensional distribution of a major desert dust outbreak over East Asia in March 2008 derived from IASI satellite observations. J. Geophys. Res. Atmos., 120, 7099–7127. doi: 10.1002/2014JD022406.Guermazi, H.; Sellitto, P.; Serbaji, M.M.; Legras, B.; Rekhiss, F. Assessment of the Combined Sensitivity of Nadir TIR Satellite Observations to Volcanic SO2 and Sulphate Aerosols after a Moderate Stratospheric Eruption. Geosciences 2017, 7, 84.Sellitto, P. and Legras, B.: Sensitivity of thermal infrared nadir instruments to the chemical and microphysical properties of UTLS secondary sulfate aerosols, Atmos. Meas. Tech., 9, 115-132, https://doi.org/10.5194/amt-9-115-2016, 2016. [ABSTRACT FROM AUTHOR]

East Asia is suffering from both severe air pollution problem due to intensive anthropogenicemissions and natural mineral dust aerosols. During transport, the aerosol particles undergocomplex mixing processes, resulting in great impacts on regional air quality, human healthand climate. In this study, we conducted a long-term observation using an Optical ParticleCounter equipped with a Polarization detection module (POPC) at an urban sitein Beijing. Mass concentrations of both PM2.5 and PM10 estimated from POPCcompared well with ground-based measurements. The results revealed that theobserved depolarization ratio (DR, termed as the ratio of the intensity of the s-polarizedsignal to the intensity of the 120 degree backward scattering signal [s/(s + p)])for aerosol particles in the fine mode was generally much lower in summer thanthat in spring as a result of predominance of different aerosol types. Mineral dustparticles in the coarse mode normally had a large DR value (0.3 ± 0.05) owing to theirnon-spherical shape; however, particles in the fine mode consisted of large proportionwater-soluble compositions, which lead to apparent decrease of their DR values inparticular high relative humidity (RH) condition. Because the observation site wassubject to frequent impact of dust event in spring, DR value of particle at 1 μm wasalmost twice as high as that (0.07 ± 0.01) in summer. Based on size-resolved DRvalues, anthropogenic pollutants, mineral dust and polluted mineral dust particles,and their contribution to local air quality were well distinguished. About 26.7%of substandard days (daily averaged PM2.5 concentration larger than 75 μg/m3)in Beijing was featured by high atmospheric loading of coarse-mode particles inwinter-spring time. In particular during severe pollution episode in winter, the DRvalues of coarse mode particles decreased by 13%, implies the high possibility ofdust-related heterogeneous processes on pollution formation. During dust event, DRvalues of particle at Dp = 5 μm decreased evidently with increase of PM2.5/PM10ratio as well as RH, indicating of the morphological changes of mineral dust. Thisstudy confirmed that high RH tends to promote water absorption processes on thedust surface as well as coating of soluble compounds, and suggested that complexmixing of dust and anthropogenic particles may lead to underestimate impact ofdust particles in urban area based on remote sensing technique, and interactionbetween dust particle and pollutants should be well considered by the optical model. [ABSTRACT FROM AUTHOR]