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Dust plays a very important role in the Earth's climate system by its direct and indirect effects. Deserts in northwestern China contribute a large amount of dust particles, both inland and outside, while the vertical distribution and transport mechanism of dust still have many uncertainties. Using Level 3 cloud-free monthly aerosol products of the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) system from 2007 to 2020, we analyzed the spatial and temporal variations and transport features for dust and polluted dust aerosols over China and the surrounding areas. The results show that the Taklimakan Desert (TD) and the Thar Desert (TRD) always act as the high-value centers of dust optical depth (DOD), while the centers of polluted dust optical depth (PDOD) are located in eastern China, the Sichuan Basin and the Indian subcontinent. The DOD shows an increasing trend in most areas, while the PDOD presents a significant decrease and increase in eastern China and central India, respectively. The largest DOD appears in spring over the TD and the Gobi Desert (GD), while the largest DOD in summer is over the TRD. Although most dusts in the TD and TRD are concentrated below 4 km, they may be higher over the TD. Most of the polluted dusts are confined to under 2 km. The dust input to the Tibetan Plateau (TP) could come from both the TD and TRD and occurs mostly in spring and summer, respectively. The polluted dusts of South Asia and the Indian subcontinent are mostly contained in the boundary layer in winter, but they could extend much higher in spring and summer, which favors their transport into southwestern China. The dust layer shows apparent seasonality. Its top reaches a higher level in spring and summer, while the base stays at a similar height in all seasons. The dust layer appears to be the thickest in spring over most areas, while the thickest layer in summer is over the TD and TRD. The polluted dust layer is thickest in the Indian subcontinent in spring. The overlapping of dust and polluted dust layers present different patterns in different regions, which suggests diverse mixture processes of dusts and pollutants. Finally, we compared and found different influences of meteorological factors, such as wind field, boundary layer height and precipitation, on the variations in DOD and PDOD over dust sources and other areas. [ABSTRACT FROM AUTHOR]

Aerosol-CCN characteristics and dynamics during a pre-monsoon dust storm (April 6–11, 2015) over a high-altitude site ((17.92°N, 73.66°E, and 1348 m above mean sea level (MSL)) in Western Ghats, India, has been studied using ground-based observations, satellite, and reanalysis datasets. Spatial distribution of dust surface mass concentration along with the back trajectory analysis showed the Arabian Desert area (Rub-Al-khali desert) as the source region and strong westerly winds transported the dust particles toward the Indian subcontinent. High values noticed in the surface PM10 (PM2.5), i.e., ~ 450 (~ 130) µg m−3, MODIS AOD550nm (0.6), and MERRA 2 dust surface mass concentration (5 × 10−7 kg m−3) along MODIS true color images confirmed the dust storm event on April 6, 2015 over the observational site. Size-segregated aerosol number concentration measured from ground-based observations showed the dominance of Aitken, accumulation, and coarse mode particles during dust period. CCN concentrations at 0.1, 0.3, 0.5, 0.7, and 0.9% SS were analyzed. A low value of CCN concentration and activation fraction (~ 0.3) near surface was noticed during dust storm day, suggesting insoluble mineral dust particle being transported. Analyzed vertical velocity during pre-dust period showed downdraft between 900 and 750 hPa, suggesting dust transport from upper altitudes toward the observational site. WRF-Chem model simulation also captured the dust storm event, and the results are in good agreement with the observation with a significance of 95% confidence level. [ABSTRACT FROM AUTHOR]

Utilizing the well-calibrated, high-spectral-resolution equal-quality performance of daytime and nighttime (09:30 and 21:30 local solar Equator-crossing time (local solar ECT)) products of the Infrared Atmospheric Sounder Interferometer (IASI) from the Laboratoire de Météorologie Dynamique (LMD), this study investigates the day–night differences in dust aerosols over the global dust belt of North Africa, the Middle East, and Asia. Both daytime dust optical depth (DOD) and nighttime DOD at 10 µ m show high consistency with solar and lunar observations of coarse-mode aerosol optical depth (CAOD) from AErosol RObotic NETwork (AERONET) sites across the dust belt, with correlation coefficients of 0.8–0.9 for most sites. Both IASI DOD and dust layer height show a significant (95 % confidence level) day–night difference over the major dust sources within the dust belt. Daytime DOD over the central to northern Sahara, the central to eastern Arabian Peninsula, and the Taklamakan Desert is significantly higher than that of nighttime but lower than nighttime over the southern Sahel to the Guinea Coast and the western to central Indian subcontinent in the annual mean. The magnitude of the day–night differences in DOD is larger and more evident in boreal winter and spring than in other seasons. The positive day–night differences in DOD (i.e., higher daytime values than nighttime) over the central Sahara, the Middle East, and Asia are likely associated with greater dust emissions driven by higher dust uplift potential (DUP) and stronger wind speeds during daytime. Dust layer heights demonstrate negative day–night differences over dust source regions in the central Sahara, central Arabian Peninsula, and Taklamakan Desert and positive height differences in the southern Sahel to the Guinea Coast, southern parts of the Arabian Peninsula, and large parts of the Indian subcontinent. The higher dust layer height over the Guinea Coast and the Indian subcontinent during the daytime is associated with a deeper planetary boundary layer height and greater convective instability during daytime than nighttime, which promotes vertical transport and mixing of dust aerosols. The corresponding lower daytime DOD over the Sahel and the Indian subcontinent indicates a possible dilution of dust aerosols when they are transported to higher altitudes by convection where they are more susceptible to horizontal transport. Ground-based observations of dust show surface PM 10 concentration and CAOD exhibit a spatially varying diurnal cycle across the dust belt. CAOD and PM 10 concentrations generally peak in late morning and from late afternoon to midnight in the Sahel and in early afternoon and around early morning in the Middle East, the timings of which are largely consistent with the day–night differences in IASI DOD. It is also found that DOD from reanalysis products (e.g., Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) and ECMWF Atmospheric Composition Reanalysis 4 (EAC4)) failed to capture the day–night differences in IASI DOD in large parts of the dust belt except in small dust source hotspots over North Africa. [ABSTRACT FROM AUTHOR]

The dust plume tracks from the Middle East and Eastern Africa to the Indian subcontinent have an impact on the atmospheric and ocean biogeochemistry of the Arabian Sea (AS). Here, we present the impact of dust on net primary productivity (NPP) over the AS using satellite-based observation and model simulation. Seasonal episodes and long-term trends in dust optical depth (DOD), dust mass flux (DMF) and dust deposition flux (DDF) from 2007 to 2020 are quantified. Nearly 32% of the total dust is advected to the AS during transport (maximum in JJA; DMF ~ 33.1 Tg year−1 ~ 56% of annual and DDF ~ 5.5 Tg year−1 ~ 63% of annual). Over the last one and half decades, there has been a statistically significant decreasing trend in DOD, associated with precipitation, enhanced vegetation index and surface soil moisture over the landmasses in the proximity of the AS. Similarly, the depletion in DDF suppresses the NPP over different regions of the AS, especially over the central AS, where the oceanic supply of nutrients is limited. [ABSTRACT FROM AUTHOR]

Through a comprehensive investigation into the historical profiles of black carbon derived from ice cores, the spatial distributions of light-absorbing impurities in snowpit samples, and carbon isotopic compositions of black carbon in snowpit samples of the Third Pole, we have identified that due to barriers of the Himalayas and remove of wet deposition, local sources rather than those from seriously the polluted South Asia are main contributors of light-absorbing impurities in the inner part of the Third Pole. Therefore, reducing emissions from residents of the Third Pole themselves is a more effective way of protecting the glaciers of the inner Third Pole in terms of reducing concentrations of light-absorbing particles in the atmosphere and on glaciers. [Display omitted] • LAPs deposited on glaciers of the inner TP are primarily sourced from the TP itself. • The Himalayas serve as barrier of transport LAPs from South Asia into inner TP. • Atmosphere of the inner TP remains largely devoid of long-range transported LAPs. [ABSTRACT FROM AUTHOR]

This study investigates the seasonal climatology of the three-dimensional distribution and transport pathways of dust aerosols over West Asia (WA). Dust column loading over WA exhibits strong seasonality, with markedly high (weak) loading during summer (winter). The summer dust features over WA include the (i) dust reaching up to the 500 hPa level between the Red Sea (RS) and the west coast of the Indian subcontinent (IS); (ii) a slantwise advection of dust aerosols between 850 and 700 hPa levels over the Arabian Peninsula (AP) and Arabian Sea (AS); and (iii) a prominent mid-tropospheric zonal transport of AP dust toward the IS. Maximum column integrated horizontal dust mass flux (DMF) over WA is observed in summer. The intraday changes in the intensity and spatial spread of the DMF over the AP are mediated by the out-of-phase evolution of the surface winds and low-level Shamal jets. Furthermore, the diurnal changes in the strength of the inversion layers located above the monsoon boundary layer and associated wind shear regulate the spatial patterns and intensity of the DMF over the AS. The findings will support future studies aiming at quantifying the radiative effects of dust on the regional climate. [ABSTRACT FROM AUTHOR]

Identification of aerosol types has long been a difficult problem over East and South Asia due to various limitations. In this study, we use 2-dimensional (2-D) and multi-dimensional Mahalanobis distance (MD) clustering algorithms to identify aerosol characteristics based on the data from the Aerosol Robotic Network from March 1998 to February 2018 over the South and East Asian region (10°N~50°N, 70°E~135°E). The single scattering albedo (SSA), absorption Angstrom exponent (AAE), extinction Angstrom exponent (EAE), real index of refraction (RRI), and imaginary index of refraction (IRI) are utilized for classification of aerosols. Sub-regions with similar background conditions over East and South Asia are identified by hierarchical clustering algorithm to illustrate distinctive meteorological states in different areas. The East and South Asian aerosols are found to have distinct regional and seasonal features relating to the meteorological conditions, land cover, and industrial infrastructure. It is found that the proportions of dust aerosol are the highest in spring at the SACOL site and in summer at the sites near the Northern Indo-Gangetic Plain area. In spring, biomass-burning aerosols are dominant over the central Indo-China Peninsula area. The aerosol characteristics at coastal sites are also analyzed and compared with previous results. The 2-D clustering method is useful when limited aerosol parameters are available, but the results are highly dependent on the sets of parameters used for identification. Comparatively, the MD method, which considers multiple aerosol parameters, could provide more comprehensive classification of aerosol types. It is estimated that only about 50% of the data samples that are identifiable by the MD method could be classified by the 2-D methods, and a lot of undetermined data samples could be mis-classified by the 2-D methods. The aerosol radiative forcing (ARF) and the aerosol radiative forcing efficiency (ARFE) of various aerosol types at the top and the bottom of the atmosphere (TOA and BOA) are determined based on the MD aerosol classification. The dust aerosols are found to have the largest ARF at the TOA (−36 W/m2), followed by the urban/industrial aerosols and biomass-burning aerosols. The ARFE of biomass-burning aerosols at the BOA (−165 W/m2/AOD550nm) is the strongest among those of the other aerosol types. The comparison of the results by MD and 2-D methods shows that the differences in ARF and ARFE are generally within 10%. Our results indicate the importance of aerosol type classification in accurately attributing the radiative contributions of different aerosol components. [ABSTRACT FROM AUTHOR]

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

The genesis, dynamics, and impacts of a severe dust storm over the central Himalaya during June 13–17, 2018 have been investigated using in situ measurements, satellite data, and model reanalysis. A low‐pressure system over northern India and prevalence of strong winds (∼20 ms−1) triggered the dust storm leading to poor visibility conditions and five‐fold enhancement in the fine particulate matter (PM2.5) over the central Himalaya. Enhancements in Aerosol Optical Depth (AOD) were observed to be stronger over the Himalayan foothills site (Lumbini) than that over the Indo‐Gangetic Plain (IGP) site‐Gandhi College. The sharp reductions in Angstrom exponent (α) from about 1.2 to 0.3 indicated the dominance of coarse‐mode aerosols during the dust episode. Model results show an enhancement in the dust from 1.5 to 2.5 Tg (∼70%) over the northern Indian subcontinent, with about half of the contribution from the regional source (Thar Desert). Interestingly, dust storm also had significant impacts on turbulent kinetic energy (2.9–9.6 m2 s−2), vertical momentum flux (0.9–3.3 Nm−2), and sensible heat flux (34.8 to −33.9 Wm−2), suggesting turbulent mixing of aerosols and cooling near the surface over the Himalayas. Our study highlights that the large‐scale dust storms exposed to additional dust and pollution from regional sources can profoundly impact the air quality, heat fluxes, and radiative balance over the northern Indian subcontinent. The study would also help in evaluating the results of climate models and to assess the impacts of dust on the hydrological processes and melting Himalayan glaciers. Key Points: A detailed investigation on the genesis, dynamics, and impacts of a severe dust storm over northern Indian subcontinent has been conductedAnalysis on the relative effects of long‐range transport and regional dust emissions affecting northern Indian subcontinent regionThe impacts of dust storm on characteristics of aerosols and the surface layer have been analyzed [ABSTRACT FROM AUTHOR]

To better understand the aerosol properties over the Arctic, Antarctic and Tibetan Plateau (TP), the aerosol optical properties were investigated using 13 years of CALIPSO (Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations) L3 data, and the back trajectories for air masses were also simulated using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results show that the aerosol optical depth (AOD) has obvious spatial- and seasonal-variation characteristics, and the aerosol loading over Eurasia, Ross Sea and South Asia is relatively large. The annual-average AODs over the Arctic, Antarctic and TP are 0.046, 0.024 and 0.098, respectively. Seasonally, the AOD values are larger from late autumn to early spring in the Arctic, in winter and spring in the Antarctic, and in spring and summer over the TP. There are no significant temporal trends of AOD anomalies in the three study regions. Clean marine and dust-related aerosols are the dominant types over ocean and land, respectively, in both the Arctic and Antarctic, while dust-related aerosol types have greater occurrence frequency (OF) over the TP. The OF of dust-related and elevated smoke is large for a broad range of heights, indicating that they are likely transported aerosols, while other types of aerosols mainly occurred at heights below 2 km in the Antarctic and Arctic. The maximum OF of dust-related aerosols mainly occurs at 6 km altitude over the TP. The analysis of back trajectories of the air masses shows large differences among different regions and seasons. The Arctic region is more vulnerable to mid-latitude pollutants than the Antarctic region, especially in winter and spring, while the air masses in the TP are mainly from the Iranian Plateau, Tarim Basin and South Asia. [ABSTRACT FROM AUTHOR]

The paper investigates the impact of atmospheric dust deposition on ocean biological productivity in association with oceanic supply of nutrients over specific regions of the Arabian Sea (20°N, 69°E) and the Bay of Bengal (20°N, 87°E) during wintertime (November–March) from the year 2012 to 2017 using satellite-based observations. During winter, selected regions are characterized by higher Chlorophyll-a (Chl-a) and major oceanic vertical supply of nutrients. Moderate Resolution Imaging Spectroradiometer onboard Aqua space-platform is used to obtain Chl-a and aerosol optical depth (AOD) data. Blended Chl-a daily product from various satellite sensors is also used. There are a total of nine cases (seven cases of the Arabian Sea region and two cases of the Bay of Bengal region) where episodic Chl-a enhancements following high AOD values are observed. Chl-a maxima lag behind AOD maxima by 1 to 4 days. Modern-Era Retrospective analysis for Research and Applications (Version-2) is used for AOD and dust deposition flux estimation. Estimated dust deposition flux ranges between 0.44 and 27.68 mg m−2 day−1. [ABSTRACT FROM AUTHOR]

Emissions and long-range transport of mineral dust and combustion-related aerosol from burning fossil fuels and biomass vary from year to year, driven by the evolution of the economy and changes in meteorological conditions and environmental regulations. This study offers both satellite and model perspectives on the interannual variability and possible trends of combustion aerosol and dust in major continental outflow regions over the past 15 years (2003–2017). The decade-long record of aerosol optical depth (AOD, denoted as τ), separately for combustion aerosol (τc) and dust (τd), over global oceans is derived from the Collection 6 aerosol products of the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard both Terra and Aqua. These MODIS Aqua datasets, complemented by aerosol source-tagged simulations using the Community Atmospheric Model version 5 (CAM5), are then analyzed to understand the interannual variability and potential trends of τc and τd in the major continental outflows. Both MODIS and CAM5 consistently yield a similar decreasing trend of -0.017 to -0.020 per decade for τc over the North Atlantic Ocean and the Mediterranean Sea that is attributable to reduced emissions from North America and Europe, respectively. On the contrary, both MODIS and CAM5 display an increasing trend of + 0.017 to + 0.036 per decade for τc over the tropical Indian Ocean, the Bay of Bengal, and the Arabian Sea, which reflects the influence of increased anthropogenic emissions from South Asia and the Middle East in the last 2 decades. Over the northwestern Pacific Ocean, which is often affected by East Asian emissions of pollution and dust, the MODIS retrievals show a decreasing trend of -0.021 per decade for τc and -0.012 per decade for τd , which is, however, not reproduced by the CAM5 model. In other outflow regions strongly influenced by biomass burning smoke or dust, both MODIS retrievals and CAM5 simulations show no statistically significant trends; the MODIS-observed interannual variability is usually larger than that of the CAM5 simulation. [ABSTRACT FROM AUTHOR]

The Indian subcontinent is a major hotspot of aerosol loading and several studies have demonstrated the importance of interaction between Asian dust aerosols and the Indian Summer Monsoon Rainfall (ISMR). However, a few studies have suggested a declining trend in the pre-monsoon dust loading over the Indian region. The present study investigates how the decrease in dust emissions influences the intensity of the monsoon rainfall over the Indian region using a fully coupled Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We have conducted two sets of simulation experiments for the June-July-August-September (JJAS) season of 2017: (1) a control experiment with the default dust aerosol emissions, and (2) a sensitivity experiment by reducing dust emissions by 60%. Our analyses show that the reduction in dust emissions significantly alters the spatial distribution of seasonal mean monsoon rainfall with enhanced rainfall over the Bay of Bengal (BoB) and eastern coastal regions, and decreased rainfall over the lower Indo-Gangetic Plain (IGP), and parts of Central India (CI). It is found that the low aerosol loading conditions alter the large-scale circulation patterns along the tropical/sub-tropical region centred between 15°N and 35°N and 40°E −130°E, and through dynamical feedback, strengthens the convective rainfall over the BoB region. As a result, the 10–20 days sub-seasonal mode of the ISMR strengthens, facilitating enhanced westward propagation of rain-bearing systems formed over northern BoB which provides substantial rainfall over vast regions of the Indian subcontinent. • The impact of dust emissions on Indian Summer Monsoon Rainfall (ISMR) is examined. • Reduction in dust emissions significantly alters spatial rainfall distribution. • Strengthening of cyclonic circulation and increase in convective activity are noted over Bay of Bengal in reduced dust scenario. • Significant impact of reduced dust emissions is noted in the 10–20 days sub-seasonal variability of ISMR. • Westward propagating systems are strengthened in the reduced dust scenario. [ABSTRACT FROM AUTHOR]

This study examines vertically resolved aerosol optical properties retrieved from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard CALIPSO satellite over several cities across South Asia from March 2010 to February 2021. Atmospheric layer-specific stratification of aerosols and dominant aerosol sub-types was recognized over each city with their seasonal trends. A contrasting pattern in aerosol vertical distribution over cities across Indo-Gangetic Plain (IGP) was noted compared to non-IGP cities, with considerable dependency on geographic location of the city itself. In all the cases, total extinction decreased with increasing altitude however, with varying degree of slope. A clear intrusion of transported aerosols at higher altitude (>3 km) was also evident. Extinction coefficient of type-separated aerosols indicate robust contribution of smoke aerosols, urban aerosols/polluted dust, and mineral dust below 3 km height. At higher altitude (>3 km), dust and urban aerosols dominate over majority of the stations. Overall, 51% of total columnar aerosols remained within 0–1 km height over South Asian cities, slightly high over the IGP (57%) against non-IGP cities (39%). Such distribution also has a seasonal pattern with higher fraction of aerosols remaining below 1 km during post-monsoon (October–November, 62%) and winter (December–February, 72%) compared to summer months (March–May, 39%). When partitioned against planetary boundary layer (PBL), 41% (59%) of aerosols remained within the PBL (free troposphere) that too exhibiting strong diurnal variations irrespective of seasons. Dominating aerosol types and their contribution to total aerosol loading was explored by comparing type-based aerosol extinction against total aerosol extinction. Dust, smoke and urban aerosols emerged as three predominating aerosol types, while presence of marine aerosol was noted over the coastal cities. Major fraction of smoke and urban aerosols remained within 2 km height from surface. In contrast, efficient transport of dust aerosol above 2 km height was evident particularly over IGP during summer. [Display omitted] • Approximately 51% and 25% of AOD remained within 0–1 km & 1–2 km height from surface. • Higher fraction of AOD found within 1 km in post-monsoon and winter compared to summer. • Boundary layer and free troposphere share 41% and 59% of AOD with marked seasonality. • Mineral dust was abundant near surface at source region but at higher height downwind. • Smoke aerosols primarily remained within 2 km across IGP in post-monsoon and winter. [ABSTRACT FROM AUTHOR]

This study examines the interannual variability of South Asian summer monsoon rainfall (SAMR) using a linear trend analysis for the recent 17-year period from 2000 to 2016. The trends in SAMR analyzed from multiple rainfall datasets show a unique crisscross like pattern over South Asia and its surrounding oceans. Significant positive trends in SAMR occur over the middle and south Bay of Bengal (BOB) and North-West India (NWI) aligned in SE-NW direction. Similarly, significant negative trends are observed over North-East India and head Bay of Bengal (NEI) as well as over the middle and south Arabian Sea (AS) oriented in SW-NE direction. Western Ghats make an exception to this pattern, where significant positive trends have been observed. Interestingly, the trends in aerosol optical depth (AOD) for the same period closely follow the trends in SAMR. The relationship of AOD averaged over each of the significant aerosol trend regions with the SAMR suggest aerosol induced suppression in moisture transport from a region covering Southern Arabian Sea and Bay of Bengal played a dominant role over the negative trend regions. However, the decreased aerosols over the Northwest India due to significant positive trends in rainfall reduced dust transport from the Arabian Peninsula towards eastern parts of South Asia resulting in an increase in anthropogenic aerosols from local sources. This caused significant drying over the NEI and AS regions through aerosol indirect effects. Further, Aerosol direct radiative effects due to natural and anthropogenic sources inferred from the climate forcing estimates confirmed their role in positive trends and the indirect effects inferred from satellite cloud products depicted a strong association with negative trends, thus maintaining the observed crisscross pattern. • Monsoon rainfall follow a crisscross pattern with the positive and negative trends distinctly associated with aerosols. • Different datasets confirm a hike in aerosol loading over South Asia except Northwest India which experienced a decrease. • Mixed aerosol effects are found to be contributing to negative rainfall trends, however, less effective in positive trends. [ABSTRACT FROM AUTHOR]

A full understanding of the Asian dust cycle can help with evaluation of the profound impact of mineral dust on human health, the ecosystem, the terrestrial and oceanic biogeochemical cycles, and the weather and climate. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)-based 3-D dust detection and routine sampling capability, with the accurate dust mass extinction efficiency from Dust Constraints from joint Observational-Modelling-experimental analysis (DustCOMM) dataset, has made it possible to estimate the climatology of Asian dust mass loading (DML) and its transport flux. This study draws on this to provide new insights into the Asian dust cycle, especially the variability of its mass-weighted dust transport central axis (TCA), the contribution of different desert sources to its downstream effects, and the resulting dust budgets in terrestrial and oceanic regions. Dust aerosols emitted from the East Asian and Central Asian deserts together form a heavy dust transport belt stretching from the Taklimakan Desert (TD) and Gobi Desert (GD) to the Pacific Ocean. South Asian dust from the Thar Desert (ThD) can also affect southern China by crossing the Hengduan Mountains and the Yunnan-Guizhou Plateau. The dust TCA is controlled by the terrain of northwest inland China, but shifts in remote regions in the range of 35-50°N due to the western Pacific subtropical high and Aleutian low, and it trend towards a zonal straight line as the altitude increases. The dust transport contribution of the East Asian deserts to the mainland of China and adjacent sea is about 7 times than that of South Asia, with the annual transport fluxes being 214.28 and 30.43 Tg, respectively. The GD dominates the contribution of Asian deserts to the downstream effects and accounts for about 60% of the dust. This can be attributed to its maximum transport flux being near the surface, while the dust transport of the TD and ThD is above 3 km because of the blocking effect of the surrounding terrain. The deposition of Asian dust in the adjacent seas decreases significantly along the dust TCA, with the annual deposition rates being about 40.12, 20.41, and 4.01 g m-2 in the Yellow Sea, Japan Sea and the Northwest Pacific Ocean, respectively. These new findings and quantification of the Asian dust cycle will help with validation of the simulations provided by global and regional climate models and enable further evaluation of the impact of Asian dust on various related Earth systems. • Asian dust transport flux and its contributor are firstly estimated using satellite. • East Asian deserts produce 88% of dust in mainland China and adjacent seas. • Gobi Desert is the largest downstream contributor of dust aerosol at 145.88 Tg y-1. • Dust transport flux from South Asia to the southern China is about 30.43 Tg y-1. • Asian dust outflow settles most in the Yellow Sea, with a value of 40 g m-2 y-1. [ABSTRACT FROM AUTHOR]

Extreme dust episodes have been noticeably increasing in recent years. Dust burden during such events imparts several threats to the environment and human health. Therefore, forecast of such extreme events becomes of utmost importance to minimise the adverse impact on various socio-economy sectors. In the present study model experiments have been carried out for the simulation of an extreme dust episode that emanated over the western Indian region that coupled with previously transported dust from the West Asia region and resulted in the highly degraded air quality over the Indian region. For this purpose four ensemble members, using Weather Research and Forecasting model fully coupled with chemistry (WRF-CHEM), have been generated for identical model configuration but for the perturbed initial conditions. Model performance has been evaluated with respect to the available ground based measurements from Central Pollution Control Board (CPCB) and the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) data sets using standard statistical measures. Ensemble spread is noted amongst the four ensemble members generated based on 4 varying initial conditions, therefore it is suggested to use ensemble mean forecast for the dust storm monitoring and analysis. It is revealed from the analysis based on the categorical validation scheme that the WRF-CHEM simulated dust load is able to capture the locational accuracy with respect to the reanalysis/observational data sets over Indian subcontinent fairly well with 0% false alarm ratio, 78–92% probability of detection and 79–90% accuracy. It is noted that thick blanket of dust load enveloped Northern part of India subsequent to the dust storm which resulted in substantially dropped ground reaching solar radiation (~100–150 W/m2) and a consequential reduction in the surface temperature (~2 °C). Further to this enhanced temperature in association with reduced relative humidity from 800 to 600 hPa has also been noted in response to the enhanced dust loading in the model simulations. Results obtained in the present study suggests that WRF-CHEM is able to simulate both the direct and semi-direct effects of dust aerosols reasonably well. Present work has implications for improved prediction skills of WRF-CHEM in simulating extreme dust episodes and investigating the impact of dust aerosols on weather and climate. • WRF-CHEM has been utilized for the simulation of an extreme dust episode. • Optimal ensemble approach has been used for the simulations. • Model output validated against observational/reanalysis data based on categorical validation scheme. • Model simulated results show a good match with the observational/reanalysis data. • WRF-CHEM demonstrates reasonable skills in simulating the dust storm, direct and semi-direct effects of dust aerosols. [ABSTRACT FROM AUTHOR]

Aerosol is a critical trace component of the atmosphere. Many processes in the Earth's climate system are intimately related to aerosols via their direct and indirect radiative effects. Aerosol effects are not limited to these climatic aspects, however. They are also closely related to human health, photosynthesis, new energy, etc., which makes aerosol a central focus in many research fields. A fundamental requirement for improving our understanding of the diverse aerosol effects is to accumulate high-quality aerosol data by various measurement techniques. Sunphotometer remote sensing is one of the techniques that has been playing an increasingly important role in characterizing aerosols across the world. Much progress has been made on this aspect in China during the past decade, which is the work reviewed in this paper. Three sunphotometer networks have been established to provide high-quality observations of long-term aerosol optical properties across the country. Using this valuable dataset, our understanding of spatiotemporal variability and long-term trends of aerosol optical properties has been much improved. The radiative effects of aerosols both at the bottom and at the top of the atmosphere are comprehensively assessed. Substantial warming of the atmosphere by aerosol absorption is revealed. The long-range transport of dust from the Taklimakan Desert in Northwest China and anthropogenic aerosols from South Asia to the Tibetan Plateau is characterized based on ground-based and satellite remote sensing as well as model simulations. Effective methods to estimate chemical compositions from sunphotometer aerosol products are developed. Dozens of satellite and model aerosol products are validated, shedding new light on how to improve these products. These advances improve our understanding of the critical role played by aerosols in both the climate and environment. Finally, a perspective on future research is presented. • Development of ground-based sunphotometer networks in China is presented. • Advances in our understanding of aerosol optical properties and radiative effects are reviewed. • A perspective on possible directions for future research is discussed. [ABSTRACT FROM AUTHOR]

Present study estimates the shortwave radiative effects of absorbing aerosols (dust and carbonaceous aerosols) over the Indian landmass using a synergy of spaceborne and ground-based observations. Vertical profiles of dust and total aerosols are estimated using the multi-year (2006–2017) observations from CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) over the Indian region. Pre-monsoon enhancement (March ‐ –May) in aerosol loading over the Indian region is significantly contributed (~56%) by the transported mineral dust at free tropospheric altitudes. Though, shortwave radiative effect due to dust in the atmosphere increases about three times from winter to pre-monsoon, at the top of the atmosphere (TOA) it causes cooling. Dust induced cooling reverses the positive radiative effect induced by non-dust aerosols at TOA over Indo-Gangetic Plains. Though the natural dust dominates the aerosol loading during pre-monsoon, anthropogenic dust contributes significantly (~65%) to the total dust loading during winter. Over Indo-Gangetic Plains, high aerosol warming (up to ~2 Kday−1) observed within the planetary boundary layer (PBL) is mainly caused by carbonaceous aerosols (85%). The observed heating rates over the Indian region can have significant implications over regional climate, air quality, and changing precipitation patterns. • Dust constitutes a major part of free-tropospheric aerosol loading in pre-monsoon. • Anthropogenic dust dominates dust loading during winter season. • Carbonaceous aerosols produce high near surface warming over Indo-Gangetic Plain. [ABSTRACT FROM AUTHOR]

We investigated aerosol optical depth (AOD) under background and polluted conditions using Aerosol Robotic Network (AERONET) and Visible Infrared Imaging Radiometer Suite (VIIRS) observations. The AOD data were separated into background, high, and median AOD (BAOD, HAOD, and MAOD, respectively) based on the cumulative AOD distribution at each point and then their spatiotemporal variations were analyzed. Persistent pollutant emissions from industrial activity in South Asia (SUA) and Northeast Asia (NEA) produced the highest BAOD values. Gridded-BAODs obtained from VIIRS Deep Blue AOD products showed widespread high-level BAOD over the oceans associated with transport from dust and biomass burning events. The temporal variations in BAOD and HAOD were generally consistent with that of MAOD, but differences were found in seasonal variation as well as in long-term trends in some regions. Southeast Asia (SEA) and South America/South Africa (SAM/SAF) showed similar HAOD levels owing to biomass burning, but BAODs were higher in SEA than in SAM/SAF. In NEA, BAOD was lowest during the summer rainy season, as opposed to the peaks in MAOD and HAOD. Long-term trends of the AODs show clear regional characteristics. The AODs have decreasing trends in NEA, Europe/Mediterranean basin, and Northeast America but increasing trends in SUA, North Africa, and the Middle East. The trend of HAOD in Northwest America and Australia was opposite to that of BAOD. The spatiotemporal patterns of the HAOD and BAOD provide detailed information on changes in aerosol loading compared to using only MAOD. • BAOD and HAOD trends reflect both natural and anthropogenic aerosol emissions. • Industrial activities have increased BAOD value in South and Northeast Asia. • The dust and biomass burning strongly enhances the HAOD level. • Both BAOD and HAOD show negative trends globally except in Africa and South Asia. • BAOD and HAOD trends could have opposite trends while mean AOD trends is steady. [ABSTRACT FROM AUTHOR]

• Characteristics of carbonaceous matter in the HTP are reviewed. • A synthesis of published HTP carbonaceous matter data is provided. • Future directions for HTP carbonaceous matter research are suggested. Carbonaceous matter, including organic carbon (OC) and black carbon (BC), is an important climate forcing agent and contributes to glacier retreat in the Himalayas and the Tibetan Plateau (HTP). The HTP – the so-called "Third Pole" – contains the most extensive glacial area outside of the polar regions. Considerable research on carbonaceous matter in the HTP has been conducted, although this research has been challenging due to the complex terrain and strong spatiotemporal heterogeneity of carbonaceous matter in the HTP. A comprehensive investigation of published atmospheric and snow data for HTP carbonaceous matter concentration, deposition and light absorption is presented, including how these factors vary with time and other parameters. Carbonaceous matter concentrations in the atmosphere and glaciers of the HTP are found to be low. Analysis of water-insoluable organic carbon and BC from snowpits reveals that concentrations of OC and BC in the atmosphere and glacier samples in arid regions of the HTP may be overestimated due to contributions from inorganic carbon in mineral dust. Due to the remote nature of the HTP, carbonaceous matter found in the HTP has generally been transported from outside the HTP (e.g., South Asia), although local HTP emissions may also be important at some sites. This review provides essential data and a synthesis of current thinking for studies on atmospheric transport modeling and radiative forcing of carbonaceous matter in the HTP. [ABSTRACT FROM AUTHOR]

Inorganic particulate nitrate (p- NO 3 −), gaseous nitric acid (HNO 3(g)) and nitrogen oxides (NO x = NO + NO 2), as main atmospheric pollutants, have detrimental effects on human health and aquatic/terrestrial ecosystems. Referred to as the 'Third Pole' and the 'Water Tower of Asia', the Tibetan Plateau (TP) has attracted wide attention on its environmental changes. Here, we evaluated the oxidation processes of atmospheric nitrate as well as traced its potential sources by analyzing the isotopic compositions of nitrate (δ15N, δ18O, and Δ17O) in the aerosols collected from the Mt. Everest region during April to September 2018. Over the entire sampling campaigns, the average of δ15N(NO 3 −), δ18O(NO 3 −), and Δ17O(NO 3 −) was −5.1 ± 2.3‰, 66.7 ± 10.2‰, and 24.1 ± 3.9‰, respectively. The seasonal variation in Δ17O(NO 3 −) indicates the relative importance of O 3 and HO 2 /RO 2 /OH in NO x oxidation processes among different seasons. A significant correlation between NO 3 − and Ca2+ and frequent dust storms in the Mt. Everest region indicate that initially, the atmospheric nitrate in this region might have undergone a process of settling; subsequently, it got re-suspended in the dust. Compared with the Δ17O(NO 3 −) values in the northern TP, our observed significantly higher values suggest that spatial variations in atmospheric Δ17O(NO 3 −) exist within the TP, and this might result from the spatial variations of the atmospheric O 3 levels, especially the stratospheric O 3 , over the TP. The observed δ15N(NO 3 −) values predicted remarkably low δ15N values in the NO x of the sources and the N isotopic fractionation plays a crucial role in the seasonal changes of δ15N(NO 3 −). Combined with the results from the backward trajectory analysis of air mass, we suggest that the vehicle exhausts and agricultural activities in South Asia play a dominant role in determining the nitrate levels in the Mt. Everest region. Image 1 • Isotopic compositions of atmospheric nitrate in Mt. Everest region were reported. • Importance of O 3 and HO 2 /RO 2 /OH in NO x oxidation processes changed among seasons. • Spatial variations in atmospheric Δ17O(NO 3 –) exist within TP. • N isotopic fractionation plays a crucial role in seasonal changes of δ15N(NO 3 –). • Vehicle exhaust and agricultural activities in South Asia are main NO x sources. Main findings: Importance of O 3 and HO 2 /RO 2 /OH in NO x oxidation processes changed among different seasons; vehicle exhausts and agricultural activities in South Asia are the main NO x sources. [ABSTRACT FROM AUTHOR]

The Arabian Sea is an enclosed basin surrounded by land and is prone to receive large amount of aeolian dust from the continent. This can significantly impact surface water biogeochemical processes. In this study, an attempt has been made to quantify the amount of dust transported from Middle East region to Indian subcontinent (sampling site is Goa; 15.45°N 73.80°E; located in the northeast Arabian Sea) via the Arabian Sea. We identified a dust storm episode (02–10 April 2015) in the Arabian Peninsula and its propagation to the study site (Goa) using satellite data (MODIS and CALIPSO). The impact of the dust storm at Goa has been computed using ambient particulate matter concentration and satellite retrieved optical parameter. These observations were further substantiated using ground-based micro-pulse lidar measurement. The daily averaged lidar profile shows relatively high depolarization ratio (0.1–0.25), as well as high daily average backscatter coefficient (up to 0.08 Sr−1 Km−1) and extinction coefficient (up to 0.9 Km−1) during the storm period compared to non-dusty days. During this period, a two-layer (rich in non-spherical particle) structure with significantly high linear depolarization ratio is observed, indicating the impact of the dust storm at the coastal region of India. Ambient mass concentration of dust estimated using CALIPSO profile are comparable with the gravimetric mass measured from high volume sample collection. The back-trajectory analysis further supports the advection of air-mass from the Middle East to Eastern Arabian Sea. This study highlight the significant role of long-range transport in impacting dust load at the remote/receptor sites. • Long-range transport of dust derived from storms can impact remote locations. • Dust concentration derived from storm is quantified using CALIPSO profile over Arabian Sea. • High altitude transport of dust, over the Arabian Sea, confirmed by LIDAR measurement. [ABSTRACT FROM AUTHOR]