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.

Duringthe summer and winter periods of 2019-2020, we conductedsampling of fine mode ambient aerosols in the western Himalayan glacialregion (WHR; Thajiwas glacier, 2799 m asl), central Himalayan glacialregion (CHR; Gomukh glacier, 3415 m asl), and eastern Himalayan glacialregion (EHR; Zemu glacier, 2700 m asl). We evaluated the aerosol opticalproperties, which included the mass absorption coefficient, mass absorptionefficiency, mass scattering efficiency, absorption angstrom exponent,single scattering albedo, as well as their simple radiative forcingefficiencies. We observed the highest absorption in the near ultraviolet-visiblewavelength range (200-400 nm), with CHR showing the highestabsorption compared to the other two sites, WHR and EHR, respectively.Across the wavelength range of 200-1100 nm, the overall contributionof black carbon to light attenuation was greater than that of browncarbon. However, brown carbon dominated the absorption in the nearUV-visible wavelengths, providing evidence of its non-trivialpresence over the Himalayan region. Additionally, we observed a positiveradiative forcing (W/g), which leads to net warming at these sites.The findings of this ground-based study contribute to our understandingof the light-absorbing nature of carbonaceous aerosols and their impacton the Himalayan glacier regions.

This study employs a fully coupled meteorology-chemistry-snow model to investigate the impacts of light-absorbing particles (LAPs) on snow darkening in the Sierra Nevada. After comprehensive evaluation with spatially and temporally complete satellite retrievals, the model shows that LAPs in snow reduce snow albedo by 0.013 (0-0.045) in the Sierra Nevada during the ablation season (April-July), producing a midday mean radiative forcing of 4.5 W m(-2) which increases to 15-22 W m(-2) in July. LAPs in snow accelerate snow aging processes and reduce snow cover fraction, which doubles the albedo change and radiative forcing caused by LAPs. The impurity-induced snow darkening effects decrease snow water equivalent and snow depth by 20 and 70 mm in June in the Sierra Nevada bighorn sheep habitat. The earlier snowmelt reduces root-zone soil water content by 20%, deteriorating the forage productivity and playing a negative role in the survival of bighorn sheep.

Light-absorbing aerosols (LAAs), mainly composed of black carbon (BC) and dust aerosols, are responsible for significant climate forcing through their strong absorption of solar radiation. A fully coupled meteorology-chemistry model (WRF-Chem) associated with satellite retrievals and in situ measurements is used to investigate the direct radiative forcing (DRF) induced by LAAs in different climate regions over East Asia. Results show that the annual all-sky dust and BC DRF are -0.84 and 1.06 W m(-2)at the top of atmosphere (TOA), -1.23 and -1.55 W m(-2)at the surface (SUR), and 0.39 and 2.61 W m(-2)within the atmosphere (ATM) over East Asia. Large LAAs DRF can be found in hyper-arid, subhumid, and humid regions at the SUR and ATM where dust DRF dominates the surface cooling effect, while BC DRF is predominant in the eminent warming effect on ATM in most climate regions. The meteorological conditions in hyper-arid region are associated with enhanced surface wind and weakened atmospheric wind, which is in favor of the emission and accumulation of dust supporting the positive LAAs DRF anomalies higher than 10 W m(-2)in hyper-arid region. The positive geopotential height anomalies over Northeast China weaken the westerly winds, which is beneficial to the accumulation of LAAs, and results in the positive LAAs DRF anomalies of 3 W m(-2)in semiarid regions. The large LAAs mass loading, strong aerosol absorptive ability, and decreased cloudiness caused by northerly anomalies are responsible for the high LAAs DRF in humid region.

Light-absorbing components of atmospheric aerosols have gained particular attention in recent years due to their climatic and environmental effects. Based on two-year measurements of aerosol absorption at seven wavelengths, aerosol absorption properties and black carbon (BC) were investigated in the North China Plain (NCP), one of the most densely populated and polluted regions in the world. Aerosol absorption was stronger in fall and the heating season (from November to March) than in spring and summer at all seven wavelengths. Similar spectral dependence of aerosol absorption was observed in non-heating seasons despite substantially strong absorption in fall. With an average absorption Angstrom exponent (alpha) of 1.36 in non-heating seasons, freshly emitted BC from local fossil fuel burning was thought to be the major component of light-absorbing aerosols. In the heating season, strong ultraviolet absorption led to an average alpha of 1.81, clearly indicating the importance of non-BC light-absorbing components, which were possibly from coal burning for domestic heating and aging processes on a regional scale. Diurnally, the variation of BC mass concentrations experienced a double-peak pattern with a higher level at night throughout the year. However, the diurnal cycle of alpha in the heating season was distinctly different from that in non-heating seasons. a peaked in the late afternoon in non-heating seasons with concomitantly observed low valley in BC mass concentrations. In contrast, alpha peaked around the midnight in the heating season and lowered down during the daytime. The relationship of aerosol absorption and winds in non-heating seasons also differed from that in the heating season. BC mass concentrations declined while alpha increased with increasing wind speed in non-heating seasons, which suggested elevated non-BC light absorbers in transported aged aerosols. No apparent dependence of alpha on wind speed was found in the heating season, probably due to well mixed regional pollution. Pollution episodes were mostly encountered under low winds and had a low level of alpha, implying aerosol absorption should be largely attributed to freshly emitted BC from local sources under such conditions. Extensive field campaigns and long-term chemical and optical measurements of light-absorbing aerosols are needed in the future to further advance our understanding on optical properties of light-absorbing aerosols and their radiative forcing in this region. (C) 2016 The Authors. Published by Elsevier Ltd.