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.

PM2.5 impacts the atmospheric temperature structure through scattering or absorbing solar radiation, whose concentration and composition can affect the impact. This study calculated the effect of PM2.5 on the temperature structures in the urban centre and the suburbs of Nanjing, as well as their differences. The results show that the optical parameters, atmospheric heating rate, radiative forcing, and temperature are all impacted by the concentration and composition of PM2.5. The uneven distribution of PM2.5 influences the differences in those factors between the urban centre and suburbs. In spring, summer, autumn, and winter, surface temperatures in the urban centre were approximately 283 K, 285 K, 305 K, and 277 K, while those in the suburbs were approximately 282 K, 283 K, 304 K, and 274 K. The urban heat island intensity has been reduced by 0.1-0.4 K due to the presence of PM2.5 in Nanjing. Due to the black carbon component's warming effect on the top of the boundary layer, the impact of PM2.5 on the urban heat island intensity profile drops quickly at the 0.75-1.25 km. PM2.5 may mask the warm city problem and have a more complex impact on the urban climate.

Air pollutants can be transported to the pristine regions such as the Tibetan Plateau, by monsoon and stratospheric intrusion. The Tibetan Plateau region has limited local anthropogenic emissions, while this region is influenced strongly by transport of heavy emissions mainly from South Asia. We conducted a comprehensive study on various air pollutants (PM2.5, total gaseous mercury, and surface ozone) at Nam Co Station in the inland Tibetan Plateau. Monthly mean PM2.5 concentration at Nam Co peaked in April before monsoon season, and decreased during the whole monsoon season (June-September). Monthly mean total gaseous mercury concentrations at Nam Co peaked in July and were in high levels during monsoon season. The Indian summer monsoon acted as a facilitator for transporting gaseous pollutants (total gaseous mercury) but a suppressor for particulate pollutants (PM2.5) during the monsoon season. Different from both PM2.5 and total gaseous mercury variabilities, surface ozone concentrations at Nam Co are primarily attributed to stratospheric intrusion of ozone and peaked in May. The effects of the Indian summer monsoon and stratospheric intrusion on air pollutants in the inland Tibetan Plateau are complex and require further studies. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V.

To understand the characteristics of particulate matter (PM) and other air pollutants in Xinjiang, a region with one of the largest sand-shifting deserts in the world and significant natural dust emissions, the concentrations of six air pollutants monitored in 16 cities were analyzed for the period January 2013-June 2019. The annual mean PM2.5, PM10, SO2, NO2, CO, and O-3 concentrations ranged from 51.44 to 59.54 mu g m(-3), 128.43-155.28 mu g m(-3), 10.99-17.99 mu g m(-3), 26.27-31.71 mu g m(-3), 1.04-1.32 mg m(-3), and 55.27-65.26 mu g m(-3), respectively. The highest PM concentrations were recorded in cities surrounding the Taklimakan Desert during the spring season and caused by higher amounts of wind-blown dust from the desert. Coarse PM (PM10-2.5) was predominant, particularly during the spring and summer seasons. The highest PM2.5/PM10 ratio was recorded in most cities during the winter months, indicating the influence of anthropogenic emissions in winters. The annual mean PM2.5 (PM10) concentrations in the study area exceeded the annual mean guidelines recommended by the World Health Organization (WHO) by a factor of ca. similar to 5-6 (similar to 7-8). Very high ambient PM concentrations were recorded during March 19-22, 2019, that gradually influenced the air quality across four different cities, with daily mean PM2.5 (PM10) concentrations similar to 8-54 (similar to 26-115) times higher than the WHO guidelines for daily mean concentrations, and the daily mean coarse PM concentration reaching 4.4 mg m(-3). Such high PM2.5 and concentrations pose a significant risk to public health. These findings call for the formulation of various policies and action plans, including controlling the land degradation and desertification and reducing the concentrations of PM and other air pollutants in the region. (C) 2020 Elsevier Ltd. All rights reserved.

Black carbon (BC) aerosols have severe impacts on climate and health. Most atmospheric BC loadings are now predominantly reported for the PM2.5 size cut-off. Based on 39 published set of ambient BC concentrations from around the world where PM2.5 and PM10 were collected in parallel, we demonstrate that BC in PM2.5 was only around 80% of that in PM10. The implication is that around 20% of BC in the global ambient atmosphere is ignored with the now-legacy PM2.5 sampling approach. Correspondingly, BC of freshly emitted particles from combustion activities is dominantly reported in terms of PM2.5, and thus inflicting a bias in the total BC emission inventories. A consequence is that ambient BC is underpredicted when derived from models based on (PM2.5) emission inventories. This consideration contributes to reconcile existing systematic offset between model predictions and observation-based estimates of climate-relevant effects of anthropogenic BC aerosols. We propose that total ambient BC concentration should be considered rather than the PM2.5 portion to reduce the uncertainties in estimates of BC effects on the climate.

Thermal-optical fractions of organic carbon (OC), elemental carbon (EC), delta C-13 and optical properties of PM(2.5 )from Vehicular Fuel Emissions (VFEs) and Biomass Mixed Fuel Emissions (BMFEs) in India were examined. Heterogeneities in these species across Bharat Stage (BS) emission standards, vehicle type and cooking processes were also captured. Results suggest that distributions of OC and EC sub-fractions and Mass Absorption Efficiency (MAE) are driven by the fuel type, operating, combustion conditions, and emissions control strategies. Variability in thermal-optical fractions of carbon was useful not only in delineating VFEs and BMFEs but also in differentiating compositionally similar sources like gasoline and diesel. The mean delta C-13 value for diesel exhaust (- 26.3 +/- 1.3 parts per thousand) was marginally higher than the value (-27.0 +/- 1.2 parts per thousand) for gasoline and BMFEs. The Brown Carbon (BrC) content in VFEs was <10% while it constituted similar to 60% of the BMFEs. The MAE of both EC and OC of all the sources were calculated at 7 wavelengths (405 nm, 445, 532, 632, 780,808, and 980 nm) and heterogeneity was observed across vehicle types (higher MAEs for MUVs), fuel type (lowest MAEoc values for gasoline-powered vehicles) and BS divisions (BSII category vehicles shown highest MAEs) along with light absorption by OC and EC emitted by these sources. The results of this study characterizing the chemical, optical and isotopic signatures of PM2.5 from three major combustion sources will be useful in enhancing source identification and resolution in source apportionment efforts and in radiative forcing calculations.

To alleviate air pollution in western China, experiencing rapid economic growth following national western development strategies, an accurate and compressive assessment of PM2.5 sources is critical. Here, we firstly investigated the spatiotemporal variation in PM2.5 and analyzed its association with weather conditions and emission changes. Then, WRF-Chem simulations were conducted for an entire year to obtain various emission sectors' contributions to the PM2.5 mass by a hybrid method, which considers both the proportions of various components as well as each sector contributing to these components. The results showed that residential emissions had the largest contribution to PM2.5 because of its dominating contribution for primary components of PM2.5 (BC and POA), which can explain > 70% of PM2.5. Seasonally, the residential contributions to PM2.5 were higher in the non-monsoon period than in the monsoon period because of the higher contribution ratios to primary components. Regionally, as an essential source of the gaseous precursors, the industrial and transportation sectors were the second-largest contributors to PM2.5 in the highly populated urban (HP) and remote background (RM) regions, respectively. Further assessment of emission reduction measures indicated that eliminating 50% of residential emissions induced a 29.4% and 33.1% decrease in the annual PM2.5 mass of the HP and RM regions, respectively, with higher decrease proportions in non-monsoon. By comparison, eliminating 50% of industrial emissions caused a significantly lower decrease in PM2.5 for both HP (10%) and RM (4.6%). Eliminating 50% of transportation emissions led to PM2.5 concentrations to decline by 9.3% in RM, which was greater than the 4.6% reduction caused by eliminating 50% of industrial emissions. Therefore, in addition to focusing on the residential sector, especially in non-monsoon in western China, the transportation sector should be a focus to alleviate PM2.5 pollution on the Tibetan Plateau. The outcome of this study provides valuable information for policy-makers to make strategies to mitigate air pollution in western China.

The optical and radiative characteristics of water-soluble and carbonaceous aerosol species in the PM2.5 samples were examined for a representative megacity over the Indo-Gangetic Basin (IGB). Aerosol optical and radiative transfer models were used to extract sulphate (SO4), nitrate (NO3), organic carbon (OC) and elemental carbon (EC) from the observations done in 2012. Initial results suggest that the mass concentration of OC dominated over other species, but impacts on optical characteristics were mostly due to the SO4 aerosols. Further, EC shows relatively large impact on radiative forcing. The aerosol optical depth (AOD) at 500 nm for SO4, NO3, EC and OC was found to be contributing similar to 36%, 20%, 27% and 9%, respectively in the total AOD value (0.61 +/- 0.18) during the entire study period. The single scattering albedo (SSA) for SO4 and NO3 was high and suggested their scattering nature; however, being the highly absorbing species, EC was found to show the lowest values of SSA during the study period. SSA for OC was, however, similar to 0.70, which was found to show the second highest warming species in the atmosphere with contribution of similar to 10%, after EC, which caused the highest warming (similar to 70%), to the total atmospheric forcing.

Particle-phase air pollution is a leading risk factor for premature death globally and impacts climate by scattering or absorbing radiation and changing cloud properties. Within the Beijing-Tianjin-Hebei region of China, where there are severe air quality problems, several municipalities have begun implementing a coal-to-electricity program that bans residential coal and provides subsidies for electricity and electric-powered heat pumps. We used GEOS-Chem to evaluate two complete residential coal-to-electricity transitions-a Beijing-off scenario and Beijing-Tianjin-Hebei-off scenario-each relative to a base case. We estimate that within China, the ambient fine particulate matter (PM2.5) reductions in the Beijing-off scenario could lead to 1,900 (95% CI: 1,200-2,700) premature deaths avoided annually, while the Beijing-Tianjin-Hebei-off scenario could lead to 13,700 (95% CI: 8,900-19,600) premature deaths avoided annually. Additionally, we estimate that the residential-coal-ban scenarios will result in a positive top-of-the-atmosphere aerosol direct radiative effect (DRE) (model domain average: Beijing-off: 0.023 W m(-2); Beijing-Tianjin-Hebei-off: 0.30 W m(-2)) and a negligible cloud-albedo aerosol indirect effect (AIE) (Beijing-off: 0.0001 W m(-2); Beijing-Tianjin-Hebei-off: 0.0027 W m(-2)). To evaluate the uncertainty of the radiative effects, we calculated the DRE under four black-carbon mixing-state assumptions and both the DRE and AIE assuming three different black-carbon-to-organic-aerosol (BC:OA) ratios for residential-coal emissions. Although the magnitude of our radiative forcing estimates varied across sensitivity cases, the domain average remained positive. When only considering the aerosol-related effects of the aforementioned coal-ban scenarios, we predict substantial health benefits, but do not anticipate a climate co-benefit, because removing aerosol emissions leads to a warming tendency. However, if the coal-to-electricity program results in less net greenhouse gas emissions due to the replacement heaters, the policy may be able to achieve health and climate co-benefits.

We estimated the current (base years) and future (2021-2100) direct radiative forcing ( DRF) of four aerosol components (water-soluble, insoluble, black carbon (BC), and sea-salt) at urban (Yeonsan (Busan) and Gwangjin (Seoul)) and background sites (Aewol and Gosan (Jeju Island)), based on a modeling approach. The analysis for base years was conducted using PM2.5 samples measured at two urban and two background sites (Yeonsan and Gwangjin: 2016, Aewol and Gosan: 2014). The future DRFs were estimated according to changes in relative humidity (RH) of RCP8.5 climate change scenario at the same sites during four different periods (PI: 2021 similar to 2040, PII: 2041 similar to 2060, PIII: 2061 similar to 2080, and PIV: 2081 similar to 2100). In addition, we compared the differences between the DRFs of future (PI similar to PIV) and base years (2016 and 2014). Overall, the water-soluble component was predominant over all other components in terms of the concentrations, optical parameters (e.g., AOD), and DRFs, regardless of sites. For the base years, the monthly patterns of total DRFs for all components and the DRFs for the water-soluble component varied with sites, and months of their highest and lowest DRFs were different depending on sites. This might be due to the combined effect of the monthly patterns of the concentrations and RHs for each site. For the differences between the DRFs of future and base years, the highest future DRFs at Yeonsan and Aewol ranged from -59 to -63 W/m(2) increasing -20 (July in PII) to -28 W/m(2) (August in PIII) compared to the base years and from -73 to -74 W/m(2) increasing -31 (July in PII) to -41 W/m(2) (September in PIV), respectively. These DRFs at Gwangjin and Gosan ranged from -79 to -84 W/m(2) increasing -29 (June in PII and PIII) to -34 W/m(2) (June in PI) and from -58 to -92 W/m(2) increasing -14 (July in PII) to -26 W/m(2) (May in PI), respectively. The high heating rates at Yeonsan (up to 4.4 K/day in November) and Aewol (up to 3.7 K/day in February) of BC component might be caused by its strong radiative absorption.