Pollutant emissions in China have significantly decreased over the past decade and are expected to continue declining in the future. Aerosols, as important pollutants and short-lived climate forcing agents, have significant but currently unclear climate impacts in East Asia as their concentrations decrease until mid-century. Here, we employ a well-developed regional climate model RegCM4 combined with future pollutant emission inventories, which are more representative of China to investigate changes in the concentrations and climate effects of major anthropogenic aerosols in East Asia under six different emission reduction scenarios (1.5 degrees C goals, Neutral-goals, 2 degrees C -goals, NDC-goals, Current-goals, and Baseline). By the 2060s, aerosol surface concentrations under these scenarios are projected to decrease by 89%, 87%, 84%, 73%, 65%, and 21%, respectively, compared with those in 2010-2020. Aerosol climate effect changes are associated with its loadings but not in a linear manner. The average effective radiative forcing at the surface in East Asia induced by aerosol-radiation-cloud interactions will diminish by 24% +/- 13% by the 2030s and 35% +/- 13% by the 2060s. These alternations caused by aerosol reductions lead to increases in near-surface temperatures and precipitations. Specifically, aerosol-induced temperature and precipitation responses in East Asia are estimated to change by -78% to -20% and -69% to 77%, respectively, under goals with different emission scenarios in the 2060s compared to 2010-2020. Therefore, the significant climate effects resulting from substantial reductions in anthropogenic aerosols need to be fully considered in the pathway toward carbon neutrality.

In the context of China's dual carbon goal, emissions of air pollutants are expected to significantly decrease in the future. Thus, the direct climate effects of black carbon (BC) aerosols in East Asia are investigated under this goal using an updated regional climate and chemistry model. The simulated annual average BC concentration over East Asia is approximately 1.29 mu g/m(3) in the last decade. Compared to those in 2010-2020, both the BC column burden and instantaneous direct radiative forcing in East Asia decrease by more than 55% and 80%, respectively, in the carbon peak year (2030s) and the carbon neutrality year (2060s). Conversely, the BC effective radiative forcing (ERF) and regional climate responses to BC exhibit substantial nonlinearity to emission reduction, possibly resulting from different adjustments of thermal-dynamic fields and clouds from BC-radiation interactions. The regional mean BC ERF at the tropopause over East Asia is approximately +1.11 W/m(2) in 2010-2020 while negative in the 2060s. BC-radiation interactions in the present-day impose a significant annual mean cooling of -0.2 to -0.5 K in central China but warming +0.3 K in the Tibetan Plateau. As China's BC emissions decline, surface temperature responses show a mixed picture compared to 2010-2020, with more cooling in eastern China and Tibet of -0.2 to -0.3 K in the 2030s, but more warming in central China of approximately +0.3 K by the 2060s. The Indian BC might play a more important role in East Asian climate with reduction of BC emissions in China.

The decadal variability of direct radiative effects of aerosols is investigated at Dibrugarh, a site in northeast India (NEI) at the eastern Himalayan foothills, primarily using multi-wavelength solar radiometer measurements spanning from October 2001 to February 2020. The ground-based aerosol observations are combined with satellite remote sensing, reanalysis data, and model simulations to study the change in atmospheric particle loading over the region. Observations indicate a statistically significant increase (similar to 0.015 yr(-1)) in Aerosol Optical Depth (AOD) during the last two decades in line with an increase in human activity. As compared to 2001-2007 (we call it as Stage I), the aerosol burden has grown rapidly during 2008 until 2020 (Stage II). AOD at 500 nm is found to increase by similar to 40% from Stage I to Stage II, resulting in an increase in the aerosol direct radiative forcing (DRF) at the top of the atmosphere (TOA) by similar to 43% during stage II (similar to-16.0 W m(-2)), from the base value of -11.2 W m(-2) in Stage I. Decreasing biomass burning activities, black carbon aerosol mass concentration, and high sulfate and organic aerosols are the primary factors responsible for the trend in TOA cooling by-0.46 W m(-2) yr(-1). This is further aided by the decrease in rainfall over NEI. MERRA-2 data analysis shows a similar enhancements in aerosol load over the entire NEI and the adjacent highly polluted Indo-Gangetic Plains (IGP). A similar feature is seen over the IGP, primarily driven by anthropogenic emissions, but precedes that in NEI by about a year. A simulation of the regional climate model (RegCM) over the south Asian domain quantifies the contribution of aerosol loading over NEI due to the aerosols carried from the IGP. In the highest aerosol loading period, about 12-30% of the aerosols, equivalent to 15-30% of atmospheric warming, are transported from the IGP to the NEI.

Black carbon (BC) aerosol is a significant, short-lived climate forcing agent. To further understand the effects of BCs on the regional climate, the warming effects of BCs from residential, industrial, power and transportation emissions are investigated in Asian regions during summer using the state-of-the-art regional climate model RegCM4. BC emissions from these four sectors have very different rates and variations. Residential and industrial BCs account for approximately 85% of total BC emissions, while power BCs account for only approximately 0.19% in Asian regions during summer. An investigation suggests that both the BC aerosol optical depth (AOD) and direct radiative forcing (DRF) are highly dependent on emissions, while the climate effects show substantial nonlinearity to emissions. The total BCs AOD and clear-sky top of the atmosphere DRF averaged over East Asia (100-130 degrees E, 20-50 degrees N) are 0.02 and +1.34 W/m(2), respectively, during summer. Each sector's BC emissions may result in a warming effect over the region, leading to an enhanced summer monsoon circulation and a subsequent local decrease (e.g., northeast China) or increase (e.g., south China) in rainfall in China and its surrounding regions. The near surface air temperature increased by 0.2 K, and the precipitation decreased by approximately 0.01 mm/day in east China due to the total BC emissions. The regional responses to the BC warming effects are highly nonlinear to the emissions, which may be linked to the influences of the perturbed atmospheric circulations and climate feedback. The nonuniformity of the spatial distribution of BC emissions may also have significant influences on climate responses, especially in south and east China. The results of this study could aid us in better understanding BC effects under different emission conditions and provide a scientific reference for developing a better BC reduction strategy over Asian regions.

Ground reaching solar radiation flux was simulated using a 1-dimensional radiative transfer (SBDART) and a 3-dimensional regional climate (RegCM 4.4) model and their seasonality against simultaneous surface measurements carried out using a CNR4 net Radiometer over a sub-Himalayan foothill site of south-east Asia was assessed for the period from March 2013-January 2015. The model simulated incoming fluxes showed a very good correlation with the measured values with correlation coefficient R-2 similar to 0.97. The mean bias errors between these two varied from -40 W m(-2) to +7 W m(-2) with an overestimation of 2-3% by SBDART and an underestimation of 2-9% by RegCM. Collocated measurements of the optical parameters of aerosols indicated a reduction in atmospheric transmission path by similar to 20% due to aerosol load in the atmosphere when compared with the aerosol free atmospheric condition. Estimation of aerosol radiative forcing efficiency (ARFE) indicated that the presence of black carbon (BC, 10-15%) led to a surface dimming by -26.14 W m(-2) tau(-1) and a potential atmospheric forcing of + 43.04 W m(-2) tau(-1). BC alone is responsible for > 70% influence with a major role in building up of forcing efficiency of + 55.69 W m(-2) tau(-1) (composite) in the atmosphere. On the other hand, the scattering due to aerosols enhance the outgoing radiation at the top of the atmosphere (ARFE(TOA) similar to -12.60 W m(-2) omega(-1)), the absence of which would have resulted in ARFE(TOA) of similar to+16.91 W m(-2) tau(-1) (due to BC alone). As a result, similar to 3/4 of the radiation absorption in the atmosphere is ascribed to the presence of BC. This translated to an atmospheric heating rate of similar to 1.0 K day(-1), with similar to 0.3 K day(-1) heating over the elevated regions (2-4 km) of the atmosphere, especially during pre-monsoon season. Comparison of the satellite (MODIS) derived and ground based estimates of surface albedo showed seasonal difference in their magnitudes (R-2 similar to 0.98 during retreating monsoon and winter; similar to 0.65 during pre-monsoon and monsoon), indicating that the reliability of the satellite data for aerosol radiative forcing estimation is more during the retreating and winter seasons.

This study assesses the direct and indirect effects of natural and anthropogenic aerosols (e.g., black carbon and sulfate) over West and Central Africa during the West African monsoon (WAM) period (June-July-August). We investigate the impacts of aerosols on the amount of cloudiness, the influences on the precipitation efficiency of clouds, and the associated radiative forcing (direct and indirect). Our study includes the implementation of three new formulations of auto-conversion parameterization [namely, the Beheng (BH), Tripoli and Cotton (TC) and Liu and Daum (R6) schemes] in RegCM4.4.1, besides the default model's auto-conversion scheme (Kessler). Among the new schemes, BH reduces the precipitation wet bias by more than 50% over West Africa and achieves a bias reduction of around 25% over Central Africa. Results from detailed sensitivity experiments suggest a significant path forward in terms of addressing the long-standing issue of the characteristic wet bias in RegCM. In terms of aerosol-induced radiative forcing, the impact of the various schemes is found to vary considerably (ranging from -5 to -25 W m(-2)).

The International Centre for Theoretical Physics (ICTP, Italy) Regional Climate Model version 3.0 (RegCM3) is used to simulate spatio-temporal distribution characteristics and radiative forcing (RF) of organic carbon (OC) aerosols in and around China. The preliminary simulation results show that OC aerosols are mostly concentrated in the area to the south of Yellow River and east of Tibetan Plateau. There is a decreasing trend of column burden of OC aerosols from south to north in China. The maximum value of column burden of OC aerosols is above 3 mg/m(2) and located in the central and southern China, southeastern Tibet, and southwestern China's Yunnan, Guizhou, Sichuan provinces. The simulation on the seasonal variation shows that the maximum value of column burden of OC aerosols appears in winter and the secondary value is in spring and the minimum in summer. The RF of OC aerosols which varies seasonally is negative at the top of the atmosphere (TOA) and surface. The spatio-temporal characteristics of the RF of OC aerosols are basically consistent with that of IPCC, implying the high accuracy of the parameterization scheme for OC aerosols in RegCM3.