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.

Aerosol optical and radiative properties play a key role in climate change. Precisely pinpointing the optical and radiative properties of various types of aerosols during diverse pollution events in urban settings remains a challenge. In this study, aerosol optical and radiative properties under contrasting pollution conditions were investigated, including dusty, haze, fireworks, and clean days, in a typical urban valley in Northwestern China, based on observations from the Sun-Sky photometers and simulations from libRadtran. The results show that on dusty days aerosols have high absorption and low backscattering, while on haze days they are characterized by fine, absorptive organic aerosol particles with pronounced forward scattering in the ultraviolet and visible spectra. On fireworks days during Chinese New Year (CNY), fine-mode aerosols from fireworks dominate, with the highest scattering and the lowest absorption under the four pollution conditions, and the particle peak radius growth responds rapidly to changes in relative humidity. Aerosols generally cause Earth's surface cooling and atmospheric warming across various pollution conditions. Notably, dusty days, clean days, and haze days all exhibit a lower positive aerosol radiative forcing (ARF) in the ultraviolet (UV) spectrum at the top of the atmosphere (TOA) due to lower single-scattering albedo (SSA). In contrast, CNY uniquely displays negative UV_ARF at TOA, attributed to high-SSA non-absorptive particles. Aerosols on dusty days have higher positive radiative forcing than on haze days, emphasizing the absorptive impact of mixed dust aerosols. These findings provide valuable insights into the behavior of aerosols under various pollution conditions in a typical urban valley, contributing to a better understanding of the environmental effects of various aerosols in arid urban regions.

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 significance of quantifying the interaction of other non-dust particles with solar radiation cannot be overemphasized. This paper presents the radiative forcing aerosol effects of some non-dust particles over four different climatic zones of West Africa. Aerosol radiative effects on solar radiation require accurate analysis of optical and radiative properties. Radiative forcing was determined by anthropogenic, dust, marine, and non-dust aerosols governed by their size distribution and concentration. A consistent increase in daily AOD values was observed with decreasing angstrom exponent. Results showed that high negative forcing was experienced in the Savanna and Guinea zones which can be attributed to the addition of black carbon and organic matter aerosols to the heavily deposited dust in the atmosphere. Non-dust and anthropogenic aerosols were found to be major contributors to the high atmospheric absorption. The result also shows that the observed variations in the aerosol properties indicate an increase in the surface cooling in the early days of February. Therefore, a larger quantity of anthropogenic and non-dust aerosols, apart from the predominant dust, could cause and boost the radiative forcing of aerosols over West Africa.

The study of urban aerosol and its influence on radiation and meteorological regime is important due to the climate effect. Using COSMO-ART model with TERRA_URB parameterization, we estimated aerosols and their radiative and temperature response at different emission levels in Moscow. Mean urban aerosol optical depth (AOD) was about 0.029 comprising 20-30% of the total AOD. Urban black carbon mass concentration and urban PM10 accounted for 86% and 74% of their total amount, respectively. The urban AOD provided negative shortwave effective radiative forcing (ERF) of -0.9 W m(-2) at the top of the atmosphere (TOA) for weakly absorbing aerosol and positive ERF for highly absorbing aerosol. Urban canopy effects decreased surface albedo from 19.1% to 16.9%, which resulted in positive shortwave ERF at TOA, while for longwave irradiance negative ERF was observed due to additional emitting of urban heat. Air temperature at 2 m decreased independently on the ERF sign, partially compensating (up to 0.5 degrees C) for urban heat island effect (1.5 degrees C) during daytime. Mean radiative atmospheric absorption over the Moscow center in clear sky conditions reaches 4 W m(-2) due to urban AOD. The study highlights the role of urban aerosol and its radiative and temperature effects.

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.

Since China implemented the Air Pollution Prevention and Control Action Plan in 2013, the aerosol emis-sions in East Asia have been greatly reduced, while emissions in South Asia have continued to increase. This has led to a dipole pattern of aerosol emissions between South Asia and East Asia. Here, the East Asian summer monsoon (EASM) responses to the dipole changes in aerosol emissions during 2013-17 are investigated using the atmosphere model of Com-munity Earth System Model version 2 (CESM2). We show that decreases in East Asian emissions alone lead to a positive aerosol effective radiative forcing (ERF) of 1.59 (+/- 0.97) W m-2 over central-eastern China (25 degrees-40 degrees N, 105 degrees-122.5 degrees E), along with a 0.09 (+/- 0.07)degrees C warming in summer during 2013-17. The warming intensified the land-sea thermal contrast and increased the rainfall by 0.32 (+/- 0.16) mm day-1. When considering both the emission reductions in East Asia and in-creases in South Asia, the ERF is increased to 3.39 (+/- 0.89) W m-2, along with an enhanced warming of 0.20 (+/- 0.08)degrees C over central-eastern China, while the rainfall insignificant decreased by 0.07 (+/- 0.16) mm day-1. It is due to the westward shift of the strengthened western Pacific subtropical high, linked to the increase in black carbon in South Asia. Based on multiple EASM indices, the reductions in aerosol emissions from East Asia alone increased the EASM strength by almost 5%. Considering the effect of the westward shift of WPSH, the dipole changes in emissions together increased the EASM by 5%-15% during 2013-17, revealing an important role of South Asian aerosols in changing the East Asian climate.

The direct perturbation of anthropogenic aerosols on Earth's energy balance [i.e., direct aerosol radiative forcing (DARF)] remains uncertain in climate models. In this study, we investigate the uncertainty of DARF associated with aerosol vertical distribution, using simulation results from 14 global models within phase 6 of the Coupled Model Intercomparison Project (CMIP6). The column mass loading for each aerosol species is first normalized to the multimodel average for each model, which is called the mass-normalization process. The unified radiative transfer model and aerosol optical parameter are used, so that the differences in the calculated DARF are solely attributed to the difference in aerosol vertical profiles. The global mean DARF values in 2014 with respect to 1850 before and after mass normalization are -0.77 +/- 0.52 and -0.81 +/- 0.12 W m(-2) respectively, assuming external mixing, which indicates that the intermodel difference in aerosol vertical distribution accounts for similar to 20% of the total DARF uncertainty. We further conduct two separate experiments by normalizing aerosol optical depth (AOD) and aerosol single scattering albedo (SSA) profiles, respectively, and find that the vertical distribution of SSA results in larger DARF uncertainty (0.17 W m(-2)) than that of AOD (0.10 W m(-2)). Finally, compared with CALIPSO observation, CMIP6 models tend to produce higher aerosol layers. The bias in modeled aerosol profile with respect to CALIPSO leads to stronger DARF, especially for land regions.

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.