Brown carbon (BrC) has been recognized as an important light-absorbing carbonaceous aerosol, yet understanding of its influence on regional climate and air quality has been lacking, mainly due to the ignorance of regional coupled meteorology-chemistry models. Besides, assumptions about its emissions in previous explorations might cause large uncertainties in estimates. Here, we implemented a BrC module into the WRF-Chem model that considers source-dependent absorption and avoids uncertainties caused by assumptions about emission intensities. To our best knowledge, we made the first effort to consider BrC in a regional coupled model. We then applied the developed model to explore the impacts of BrC absorption on radiative forcing, regional climate, and air quality in East Asia. We found notable increases in aerosol absorption optical depth (AAOD) in areas with high OC concentrations. The most intense forcing of BrC absorption occurs in autumn over Southeast Asia, and values could reach around 4 W m(-2). The intensified atmospheric absorption modified surface energy balance, resulting in subsequent declines in surface temperature, heat flux, boundary layer height, and turbulence exchanging rates. These changes in meteorological variables additionally modified near-surface dispersion and photochemical conditions, leading to changes of PM2.5 and O-3 concentrations. These findings indicate that BrC could exert important influence in specific regions and time periods. A more in-depth understanding could be achieved later with the developed model.

China experiences severe particulate matter (PM) pollution. Although a monitoring network for PM2.5 (diameter < 2.5 mu m) has been set up in more than 100 major Chinese cities, insufficient spatial coverage of observations limits the study of the temporal and spatial characteristics, influencing factors, and component of PM2.5. In this study, we conducted a one year air quality simulation using a regional climate-chemistry model and evaluated the simulation's performance based on in situ observations concerning meteorological elements and PM2.5 concentrations. The simulated results showed that, higher PM2.5 concentrations appeared in northern China and the Sichuan Basin, and the maximal value occurred in winter. Furthermore, Vertical PM2.5 concentrations presented a gradual decreasing trend from the surface, whereas in southern coastal cities the profiles were unsteady with a secondary peak in the lower layer. Meteorological conditions were conducive to both pollutant diffusion and removal in summer, whereas stagnant conditions appeared in winter, characterized by high sea level pressure (SLP), the lowest planetary boundary layer height (PBLH), and 2-m temperature (T2). In provincial capital cities, PM2.5 was positively correlated with residential emissions but negatively correlated with precipitation, 10-m wind speed, T2, PBLH, and industrial emissions. Finally, we utilized the simulation results to investigate the component variations of PM2.5. Results indicated that primary PM2.5 components had significantly higher concentrations in northern China where residential heating is the major source of PM2.5 emissions, whereas they had lower concentrations in southern China. Secondary components played a crucial role in PM2.5 mass in eastern China. This study provided a clear perspective of seasonal variations, horizontal and vertical distributions of PM2.5 and its components and influence factors, which could be used in subsequent studies to investigate the formation mechanism and emission sources of PM2.5.

The lockdowns implemented during the coronavirus disease 2019 (COVID-19) pandemic provide a unique opportunity to investigate the impact of emission sources and meteorological conditions on the trans-boundary transportation of black carbon (BC) aerosols to the Tibetan Plateau (TP). In this study, we conducted an integrative analysis, including in-situ observational data, reanalysis datasets, and numerical simulations, and found a significant reduction in the trans-boundary transport of BC to the TP during the 2020 pre-monsoon season as a result of the lockdowns and restrictive measures. Specifically, we observed a decrease of 0.0211 mu g m- 3 in surface BC concentration over the TP compared to the 2016 pre-monsoon period. Of this reduction, approximately 6.04 % can be attributed to the decrease in emissions during the COVID-19 pandemic, surpassing the 4.47 % decrease caused by changes in meteorological conditions. Additionally, the emission reductions have weakened the transboundary transport of South Asia BC to the TP by 0.0179 mu g m � 2s 1; indicating that the recurring spring atmospheric pollution from South Asia to the TP will be alleviated through the reduction of anthropogenic emissions. Moreover, it is important to note that BC deposition on glaciers contributes significantly to glacier melting due to its enrichment, posing a threat to the water sustainability of the TP. Therefore, urgent measures are needed to reduce emissions from adjacent regions to preserve the TP as the Asian Water Tower.

In this study, in situ observations were conducted for six criteria air pollutants (PM2.5, PM10, SO2, NO2, CO, and O-3) at 23 sites in western China for 1 year. Subsequently, the detailed Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) results for the pollutants were determined. The WRF-Chem model provided a clear perspective on the spatiotemporal distribution of air pollutants. High pollutant concentrations were mainly observed over highly populated mega-city regions, such as Sichuan and Guanzhong basins, whereas low concentration levels were observed over the Tibetan Plateau (TP). The TP also showed an increased concentration of O-3. Seasonally, all six pollutants except O-3 exhibited high concentration values during winter and low values during summer. O-3 concentrations exhibited an opposite seasonal variation in low-altitude regions. Unlike other pollutants that exhibited gradually decreasing concentrations with an increase in altitude, O-3 concentrations revealed an increasing trend. Furthermore, NO2 concentrations gradually increased in the upper atmosphere possibly due to lighting and stratospheric transmission. Atmospheric pollution is closely related to emissions and meteorological variations in western China. Meteorological conditions in the summer are conducive to pollutant dispersion and wet scavenging; however, unfavourable weather conditions (high pressure as well as a low planetary boundary layer height and precipitation level) in the winter can further worsen air pollution. Atmospheric pollutants from various emission sectors generally exhibited varying monthly profiles. In six typical cities, pollutants were positively correlated with multiple emission sources except for industrial emissions. Further sensitivity simulations indicated that eliminating residential emissions resulted in the largest decrease (up to 70%) in PM2.5 and PM10 concentrations. The most significant reductions in the concentrations of SO2 and NO2 were achieved by eliminating industrial and transportation emissions, respectively. The outcomes of this study could be helpful for future studies on pollution formation mechanisms as well as environmental and health risk assessments in western China. (C) 2019 Elsevier Ltd. All rights reserved.

This study discusses year-long (October 2016-September 2017) observations of atmospheric black carbon (BC) mass concentration, its source and sector contributions using a chemical transport model at a high-altitude (28 degrees 12'49.21 '' N, 85 degrees 36'33.77 '' E, 4900 masl) site located near the Yala Glacier in the central Himalayas, Nepal. During a field campaign, fresh snow samples were collected from the surface of the Yala Glacier in May 2017, which were analysed for BC and water-insoluble organic carbon mass concentration in order to estimate the scavenging ratio and surface albedo reduction. The maximum BC mass concentration in the ambient atmosphere (0.73 mu g m(-3)) was recorded in the pre-monsoon season. The BC and water-insoluble organic carbon analysed from the snow samples were in the range of 96-542 ng g(-1) and 152-827 ng g(-1), respectively. The source apportionment study using the absorption Angstrom exponent from in situ observations indicated approximately 44% contribution of BC from biomass-burning sources and the remainder from fossil-fuel sources during the entire study period. The source contribution study, using model data sets, indicated similar to 14% contribution of BC from open-burning and similar to 77% from anthropogenic sources during the study period. Our analysis of regional contributions of BC indicated that the highest contribution was from both Nepal and India combined, followed by China, while the rest was distributed among the nearby countries. The surface snow albedo reduction, estimated by an online model - Snow, Ice, and Aerosol Radiation - was in the range of 0.8-3.8% during the pre-monsoon season. The glacier mass balance analysis suggested that BC contributed to approximately 39% of the total mass loss in the pre-monsoon season. (C) 2021 The Authors. Published by Elsevier Ltd.

Black carbon (BC) exerts potential effect on climate, especially in the Tibetan Plateau (TP), where the cryosphere and environment are very sensitive to climate change. Although transport of atmospheric BC from South and East Asia to the TP has been comprehensively investigated, transport of BC from Central and West Asia (CWA) to the TP and its climate effect on the region have received little attention and are warrant investigation. Therefore, based on the observation and ERA-Interim reanalysis data, this study investigated transport of atmospheric BC from CWA to the TP, its seasonality and climate effect over the TP using WRF-Chem model. On an annual scale, BC from CWA contributes to 5.8% of total BC over the TP. Seasonally, the contribution rates were 5.1%, 5.9%, 6.2%, and 5.7% in spring, summer, autumn, and winter, respectively. The area-averaged surface radiative forcing over the TP induced by BC from CWA ranged from-0.14 to-0.04 W m(-2), with the largest and smallest negative radiative forcing occurring in autumn and winter, respectively. Affected by BC from CWA, the area-averaged surface temperature over the TP increased by 0.033 degrees C in summer, whereas it decreased by 0.002, 0.005, and 0.001 degrees C in spring, autumn and winter, respectively. In the atmosphere over the TP, the positive radiative forcing with values of 0.17, 0.20, 0.04, and 0.07 W m(-2) were induced by BC from CWA in spring, summer, autumn, and winter, respectively. At the top of the atmosphere over the TP, the calculated radiative forcing associated with BC from CWA were 0.08, 0.14,-0.1, and 0.03 W m(-2) in spring, summer, autumn, and winter, respectively. On an annual scale, the radiative forcing in the atmosphere and at the top of the atmosphere over the TP caused by BC from CWA were 0.12 W m(-2) and 0.04 W m(-2), respectively. This study enriched the theoretical connotation of transboundary transport of BC aerosols to the TP.

The Pan-Third Pole contains the largest number of glaciers outside the polar region that plays a crucial role in atmospheric circulation and the hydrological cycle. However, this pristine region has undergone rapid change through complex interactions including the black carbon (BC) enhanced warming effect and glacier melting. Study shows, Weather Research and Forecasting coupled with Chemistry (WRF-Chem) simulation is able to capture distinctive seasonal variability of BC. The result from our sensitivity experiments revealed that South Asia (SA; 60.7%) and East Asia (EA; 32.9%) contributed more toward the Tibetan Plateau (TP). Our analysis on aerosol-boundary feedback interaction revealed BC expand planetary boundary layer height by 5.0% and 4.8% over SA and EA, respectively, which facilitates BC dispersion and transportation. Whereas, we also found that under the influence of different wind regimes the significant BC transport flux aloft over the TP and the upper troposphere and lower stratosphere. Additionally, mountain-valley channel and synoptic and local meteorological processes also facilitated BC transport to the TP. This study also evaluated the effect of BC on direct radiative forcing and calculated subsequent temperature changes. A strong dimming effect of BC corroborated with the following negative surface temperature changes. However, enhanced BC concentration during winter and spring caused the increase in temperature over the TP. Here, the WRF-Chem model, synergy on aerosol-boundary feedback, BC transport flux, and source-receptor methods confirmed the significant BC contribution and transportation, and notable BC-induced warming over TP. Such trans-Himalayan BC transport and associated warming could grim glacier melt and water availability in the region.

Black carbon (BC) as the main component of pollutants in the Arctic plays an important role on regional climate change. In this study, we applied the regional climate-chemistry model, WRF-Chem, to investigate the spatial distribution, transportation, and impact factors of BC in the Arctic. Compared with reanalysis data and observations, the WRF-Chem performed well in terms of the seasonal variations of meteorological parameters and BC concentrations, indicating the applicability of this model on Arctic BC simulation works. Our results showed that the BC concentrations in the Arctic had an obviously seasonalvariation pattern. Surface BC concentrations peaked during winter and spring seasons, while the minimum occurred during summer and autumn seasons. For the vertical distribution, BC aerosols mainly concentrated in the Arctic lower troposphere, and most of BC distributed near the surface during winter and spring seasons and in the higher altitude during other seasons. The seasonality of BC was associated with the seasonal change of meteorological field. During winter, the significant northward airflow prevailing in northern Eurasia caused the transport of accumulated pollutants from this region into the Arctic. The similar but weakened northward airflow pattern and the anticyclone activity during spring can allow pollutants to be transported to the Arctic lower troposphere. Moreover, the more stable atmosphere during winter and spring seasons made BC accumulated mainly near the surface. During summer and autumn seasons, the less stable boundary layer and the cyclone activity in the Arctic facilitated the diffusion of pollutants into the higher altitude. Meanwhile, the higher relative humidity can promote the wet removal process and lead to the relatively lower BC concentrations near the surface. Compared with the seasonal change of emission, our analysis showed that the seasonal variation of meteorological field was the main contributor for the seasonality of BC in the Arctic. (C) 2019 Elsevier Ltd. All rights reserved.

The Pan-Third Pole contains the largest number of glaciers outside the polar region that plays a crucial role in atmospheric circulation and the hydrological cycle. However, this pristine region has undergone rapid change through complex interactions including the black carbon (BC) enhanced warming effect and glacier melting. Study shows, Weather Research and Forecasting coupled with Chemistry (WRF-Chem) simulation is able to capture distinctive seasonal variability of BC. The result from our sensitivity experiments revealed that South Asia (SA; 60.7%) and East Asia (EA; 32.9%) contributed more toward the Tibetan Plateau (TP). Our analysis on aerosol-boundary feedback interaction revealed BC expand planetary boundary layer height by 5.0% and 4.8% over SA and EA, respectively, which facilitates BC dispersion and transportation. Whereas, we also found that under the influence of different wind regimes the significant BC transport flux aloft over the TP and the upper troposphere and lower stratosphere. Additionally, mountain-valley channel and synoptic and local meteorological processes also facilitated BC transport to the TP. This study also evaluated the effect of BC on direct radiative forcing and calculated subsequent temperature changes. A strong dimming effect of BC corroborated with the following negative surface temperature changes. However, enhanced BC concentration during winter and spring caused the increase in temperature over the TP. Here, the WRF-Chem model, synergy on aerosol-boundary feedback, BC transport flux, and source-receptor methods confirmed the significant BC contribution and transportation, and notable BC-induced warming over TP. Such trans-Himalayan BC transport and associated warming could grim glacier melt and water availability in the region.

The formation mechanism of air pollution events in the Sichuan Basin (SB), which is the fourth most heavily polluted area in China, has not been fully revealed. This study investigated the formation mechanism of a severe air pollution event over the SB using synoptic approaches and model simulations. The results can be summarized as follows: (1) Heavy air pollution in the SB was characterized by low visibility, low atmospheric boundary layer (ABL) height, high temperature, high relative humidity, strong temperature inversion layer, subsidence in the troposphere, high water vapor content between 500 and 900 hPa, southerly winds in the low troposphere, and surface winds with low speed and irregular direction. (2) Air quality in the SB was closely related to the weather system at 700 hPa over the basin. When the 700 hPa weather system affecting the SB was a high-pressure system, the subsidence and stable atmospheric stratification increased the air pollutant concentrations near the ground. When the 700 hPa weather system affecting the SB was a low-pressure system and the basin was in front of this low-pressure system, southwesterly warm and moist airflow and adiabatic subsidence warming formed the thick temperature inversion layer over the basin. As a result, the temperature inversion layer trapped air pollutants in the basin and induced the heavy air pollution event. When the 700 hPa weather system over the SB was a low-pressure system and the basin was behind the low-pressure system, the dry and cold airflow from the north invaded southward to the basin and broke the temperature inversion layer. Consequently, air pollutants dispersed vertically, resulting in decreased concentrations near the ground. (3) Air pollutants from December 17, 2017 to January 4, 2018 were mainly from local emissions. (4) The WRF-Chem model not only reproduced the variations in PM2.5 concentrations, the ABL height, and the height-time cross-sections of temperature, water vapor content, and wind over Chengdu during the air pollution event, but also revealed the formation mechanism of this heavy air pollution event. The results of this study reveal the formation mechanism of winter heavy air pollution events over the SB and help develop effective regional air quality management strategies to reduce the likelihood of local air pollution events and minimize the adverse impacts of air pollution.