Light-absorbing organic carbon (i.e., brown carbon, BrC) significantly contributes to light absorption and radiative forcing in the atmospheric particles. However, the secondary formation of BrC and optical properties of secondary BrC are poorly understood. In this study, we analyzed and evaluated the light absorption and environmental effects of BrC and secondary BrC from July 1st to 31st, 2022 (summer) and January 20th to February 20th, 2023 (winter) in Chongqing. BrC and secondary BrC light absorption were estimated via a seven- wavelength aethalometer and the statistical approach. The average values of secondary BrC light absorption (Abs(BrC,sec,lambda)) accounted for 46.2-56.5% of Abs(BrC). Abs(BrC,370) and Abs(BrC,sec,370) were significantly higher during winter (26.2 +/- 13.2 and 9.1 +/- 5.2 Mm(-1) respectively) than that during summer (7.2 +/- 4.1 and 5.2 +/- 3.5 Mm(-1) respectively) (p < 0.001), suggesting secondary formation played an essential role in BrC. A diurnal cycle of Abs(BrC,sec,370) was explained by the photobleaching of light-absorbing chromophores under the oxidizing conditions in the daytime, and the formation of chromophores via aqueous reactions with NH(4)(+ )and NO(x )after sunset during winter. PSCF analysis showed that transport of anthropogenic emissions from the northeastern and southeastern areas of Chongqing was the important source of the secondary BrC in PP during winter. During winter, the average values of SFEBrC and SFEBrC,sec were 31.9 and 27.4 W g(-1) lower than that during summer (64.7 and 44.5 W g(-1)), respectively. In contrast, J[NO2] values of SFEBrC and SFEBrC,sec decreased by 23.3% and 8.7% during winter higher than that during summer (19.9% and 5.6%), indicating that BrC and secondary BrC cause substantial radiative effects and atmospheric photochemistry. Overall, this study is helpful in understanding the characterization and secondary formation of BrC and accurately evaluating the environmental effects of BrC in Chongqing.

Char-EC and soot-EC in the atmosphere produced from different fuel combustion have distinct optical properties which lead to different radiative forcing. Pollutants transported into high-altitude environment could have a long-lasting radiative effect due to being free of deposition. In this study, the mass absorption cross- (MAC), the sources, transport pathways and the direct radiative effects (DREs) of soot-EC and char-EC were investigated at a peak of Mountain Hua (Mt. Hua) in China. The measurement results showed that soot-EC and char-EC account for 15.7 % and 84.3 % of EC, respectively. The mean MAC (lambda = 633 nm) of soot-EC (13.7 +/- 3.8 m(2)/g) was much higher than that of char-EC (5.4 +/- 2.5 m(2)/g), indicating a stronger light absorption ability for soot-EC. During the study period, 62.1 % char-EC was from anthracite chunk coal, 24.3 % of it from liquid fuel combustion. By contrast, 59.0 % soot-EC from liquid fuel combustion and 36.6 % of it from anthracite chunk coal. EC (both char-EC and soot-EC) produced from anthracite chunk coal reached the peak of the Mt. Hua primarily through the raising of the planetary boundary layer (PBL), while the EC produced from liquid fuel arrived the peak mainly by the regional transport above the PBL of the site. Although soot-EC has a stronger ability (2.8 times higher) to absorb the light compared with char-EC, its DRE (5.7 +/- 3.9 W m(-2)) was lower than that of char-EC (11.6 +/- 6.9 W m(-2)) due to the smaller mass quantity. Liquid fuel consumption contributed 3.5 +/- 2.9 W m(-2) DRE of soot-EC, while the combustion of anthracite chunk coal contributed 7.5 +/- 5.7 W m(-2) DRE of char-EC. This study highlights the differences in DREs of soot-EC and char-EC from fossil fuel combustion and the DRE mass efficiency of soot-EC and char-EC. The results emphasize the divergent climate warming effects caused by the combustion of different fossil fuels and imply that setting path to a green transition of energy use would benefit reducing the EC perturbation to the radiation balance of earth-atmosphere.

The impact of aerosols, especially the absorbing aerosols, in the Himalayan region is important for climate. We closely examine ground-based high-quality observations of aerosol characteristics including radiative forcing from several locations in the Indo-Gangetic Plain (IGP), the Himalayan foothills and the Tibetan Plateau, relatively poorly studied regions with several sensitive ecosystems of global importance, as well as highly vulnerable large populations. This paper presents a state-of-the-art treatment of the warming that arises from these particles, using a combination of new measurements and modeling techniques. This is a first-time analysis of its kind, including ground-based observations, satellite data, and model simulations, which reveals that the aerosol radiative forcing efficiency (ARFE) in the atmosphere is clearly high over the IGP and the Himalayan foothills (80-135 Wm(-2) per unit aerosol optical depth (AOD)), with values being greater at higher elevations. AOD is >0.30 and single scattering albedo (SSA) is similar to 0.90 throughout the year over this region. The mean ARFE is 2-4 times higher here than over other polluted sites in South and East Asia, owing to higher AOD and aerosol absorption (i.e., lower SSA). Further, the observed annual mean aerosol induced atmospheric heating rates (0.5-0.8 Kelvin/day), which are significantly higher than previously reported values for the region, imply that the aerosols alone could account for >50 % of the total warming (aerosols + greenhouse gases) of the lower atmosphere and surface over this region. We demonstrate that the current state-of-the-art models used in climate assessments significantly underestimate aerosol-induced heating, efficiency and warming over the Hindu Kush - Himalaya - Tibetan Plateau (HKHTP) region, indicating a need for a more realistic representation of aerosol properties, especially of black carbon and other aerosols. The significant, regionally coherent aerosol induced warming that we observe in the high altitudes of the region, is a significant factor contributing to increasingair temperature, observed accelerated retreat of the glaciers, and changes in the hydrological cycle and precipitation patterns over this region. Thus, aerosols are heating up the Himalayan climate, and will remain a key factor driving climate change over the region.

Absorbing aerosols have significant influences on tropospheric photochemistry and regional climate change. Here, the direct radiative effects of absorbing aerosols at the major AERONET sites in East Asia and corresponding impacts on near-surface photochemical processes were quantified by employing a radiation transfer model. The average annual aerosol optical depth (AOD) of sites in China, Korea, and Japan was 1.15, 1.02 and 0.94, respectively, and the corresponding proportion of absorbing aerosol optical depth (AAOD) was 8.61%, 6.69%, and 6.49%, respectively. The influence of absorbing aerosol on ultraviolet (UV) radiation mainly focused on UV-A band (315-400 nm). Under the influence of such radiative effect, the annual mean near-surface J[NO2] (J[(OD)-D-1]) of sites in China, Korea, and Japan decreased by 16.95% (22.42%), 9.61% (13.55%), and 9.63% (13.79%), respectively. In Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) region, the annual average AOD was 1.48 and 1.29, and the AAOD was 0.14 and 0.13, respectively. The UV radiative forcing caused by aerosols dominated by black carbon (BC-dominated aerosols) on the surface was -3.19 and -2.98 W m(-2), respectively, accounting for about 40% of the total aerosol radiative forcing, indicating that the reduction efficiency of BC-dominated aerosols on solar radiation was higher than that of other types of aerosols. The annual mean J[NO2] (J[(OD)-D-1]) decreased by 14.90% (20.53%) and 13.71% (18.20%) due to the BC-dominated aerosols. The daily maximum photolysis rate usually occurred near noon due to the diurnal variation of solar zenith angle and, thus, the daily average photolysis rate decreased by 2-3% higher than that average during 10:00-14:00.

Recent satellite observations of atmospheric aerosol loading over Asia indicate a dipole pattern in the aerosol optical depth (AOD) with a substantial decrease in AOD over East Asia and persistent increase in AOD over South Asia, the two global hotspots of aerosol emissions. Aerosol emissions over Asia are also changing rapidly. However, the evolution of physical, optical and chemical columnar aerosol characteristics, and their radiative effects over time, and the resultant impacts of such evolving trends on climate and other associated risks are not yet properly quantified, and used in climate impact assessments. In order to do so, we closely examine, in addition to satellite observations, for the first time, high-quality, ca. two-decade long ground-based observations since 2001 of aerosols and their radiative effects from several locations in the Indo-Gangetic Plain (IGP) in South Asia and the North China Plain (NCP) in East Asia. A clear divergence in the trends in AODs is evident between the IGP and the NCP. The single scattering albedo (SSA) is increasing, and the absorption AOD due to carbonaceous aerosols (AAOD(CA)) is decreasing over both regions, confirming that aerosols are becoming more scattering in nature. The trends in observed aerosol content (AOD) and composition (SSA) are statistically significant over Kanpur in the IGP and Beijing in the NCP, two locations with longest ground-based records. The aerosol radiative forcing of atmosphere (ARF(ATM)) and resultant atmospheric heating rate (HR) are decreasing over both regions. However, current regionally coherent and high annual HR of 0.5-1.0 K day(-1) has severe implications to climate, hydrological cycle, and cryosphere over Asia and beyond. These results based on high-quality observations over a large spatial domain are of great significance and are crucial for modelling and quantifying aerosol-climate interactions. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

Recent increases in surface temperature and snow melt acceleration in the Himalayan region are influenced by many factors. Here we investigate the influence of absorbing aerosols, including black carbon and dust, on surface temperature and snow melt in western, central, and eastern parts of the India-Nepal Himalayan region (INHR). We compare 40-y simulations (1971-2010) one with all evolving forcing agents representative of a present-day aerosol scenario, compared to a low aerosol forcing scenario. The difference between these scenarios shows a significant increase in surface air temperature, with higher warming in parts of Western and Central Himalaya (-0.2-2 degrees C) in the months of April and May. Higher absorbing aerosol (BC and dust abundance) both at the surface and in the atmospheric column, in the present-day aerosol simulations, led to increases in atmospheric radiative forcing and surface shortwave heating rate forcing (SWHRF), compared to the low aerosol forcing case. Therefore, the absorbing aerosols cause anomalous atmospheric heat energy transfer to land due to high surface SWHRF and changes in surface energy flux, leading to snow melt. The present model version did not parameterize snow albedo feedback, which would increase the magnitudes of the changes simulated here. (C) 2021 Elsevier B.V. All rights reserved.

Regional heterogeneity in direct and snow albedo forcing of aerosols over the Himalayan cryosphere was investigated using a regional climate model coupled with the community land model having snow, ice and aerosol radiation module. Deposition of absorbing aerosols like dust (natural) and black carbon (BC) (anthropogenic) decreases the snow albedo (snow darkening) over the Himalayas. Western Himalayas experiences a large reduction in the snow albedo (0.037) despite having lower BC mass concentration compared to central (0.014) and eastern (0.005) Himalayas. The contribution of BC and dust to the snow albedo reduction is comparable over the western and eastern Himalayas. The inclusion of aerosol-induced snow darkening in to the model reduces its bias with respect to the satellite derived surface albedo by 59%, 53% and 35% over western, central and eastern Himalayas respectively during the spring season. Since surface albedo decides the sign and magnitude of aerosol direct radiative forcing, aerosol induced snow darkening significantly affects the direct radiative effects of aerosols. Hence, the aerosol-induced decrease in snow albedo causes an early reversal in the sign of aerosol direct radiative forcing at the top of the atmosphere from warming to cooling over the western and central Himalayas, which can have implications in the radiation balance and water security over the region.

Aerosol radiative properties using recently available high-quality columnar aerosol data collected at several AERONET sites in South Asia, with a focus on pollution outflow from continental South Asia observed over Hanimaadhoo in Maldives, a small island in northern Indian Ocean are quantified. The seasonal mean aerosol optical depth (AOD) over Hanimaadhoo is >= 0.3 (except ca. 0.2 during monsoon season), and single scattering albedo (SSA) is > 0.90 in all seasons. Fine mode aerosols contribute dominantly to AOD. SSA decreases as a function of wavelength due to influence of continental aerosols, except during the monsoon season when its spectral trend reverses due to increase in dust. Carbonaceous aerosols dominate (>90%) contribution to absorption AOD (AAOD). Black carbon (BC) and brown carbon (BrC) contribute >75% and -25 Wm(-2), > -20 Wm(-2) and similar to+20 Wm(-2), respectively. Aerosol loading and atmospheric heating have increased over this background site over the last decade. A regional-scale analysis of aerosol properties and radiative effects across and surrounding the Indo-Gangetic Plain (IGP) shows that AOD is >= 0.3 over entire region, and aerosols reduce seasonally 30-50 Wm(-2) of solar radiation reaching the surface, contributing significantly to solar dimming effect. The atmospheric solar heating rate due to aerosols (HR) is >= 1 K day(-1) across IGP. These high ARFs, ARFE(SFC) and HR, and increasing trends have significant implications to climate and hydrological cycle over South Asia and beyond.

We use Aerosol Robotic Network (AERONET) observation data to empirically determine how natural and anthropogenic aerosol categories (i.e. mineral dust, biomass burning, and urban-industrial aerosols) affect light extinction, showing that their radiative forcing varies strongly with the surface albedo. Generally, the radiative forcing depends on the aerosol loading, but the efficiency varies with the aerosol type and aerosol-radiation-surface interactions. Desert dust, biomass burning and urban-industrial aerosols can exhibit dramatic shifts in radiative forcing at the top of the atmosphere, from cooling to warming, at surface albedos from below 0.5 to above 0.75. Based on the linear relationship between the radiative forcing efficiency and surface albedo for aeolian aerosols, using Moderate Resolution Imaging Spectroradiometer (MODIS) AOT (Aerosol Optical Thickness) and surface albedo data, we characterized a large Asian dust event during the spring of 2001, and demonstrate its immense spatially varying radiative forcing, ranging from about -84.0 to +69.3 W/m(2). For extensive Russian wildfires during the summer of 2010, strong radiative cooling forcing variability of biomass combustion aerosols is found, ranging from about -86.3 to +3.1 W/m(2). For a thick urban-industrial aerosol haze over northern India during the winter of 2017, a large range of about -85.0 to -0.3 W/m(2) is found. These wide ranges underscore the need to accurately define aerosol-radiation-surface interactions.

The concentrations, optical and radiative effects of carbonaceous aerosols were essential to studies of the climatic, environmental and health effects. The previous studies less combined numerical simulation with in-situ observations, especially for the aerosol vertical profiles. In this study, we off-line measured vertical profiles of submicron black carbon (BC) aerosols and on-line obtained aerosol optical properties over urban Lanzhou during 26 December 2017 to 11 January 2018. The BC optical properties and radiative effects were evaluated using Optical Properties of Aerosols and Clouds (OPAC) and Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) models. The absorption and scattering coefficients and optical depth of BC aerosols ranged from 9 to 83 M m(-1) , 3-24 M m(-1) and 0.02 to 0.2 respectively, which in average accounted for 50%, 3% and 11% of the optical properties of total aerosols during the study period. BC aerosol radiative forcing (ARF) within ATMOS (top-surface) varying from 16.6 to 108.8 W m(-2) accounted for 17.3%-97.4% of total aerosols ARF with an average of 66.6%, and the percentages increased significantly as BC concentrations increased during the period. The mean atmospheric heating rate (AHR) induced by BC aerosols was 1.94 K day(-1) ranging from 0.46 to 3.03 K day(-1) during the study period. This study contributes to understanding the impacts of light-absorbing aerosols on climate and haze pollution in an urban valley.