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.

Black carbon (BC) aerosol is a significant and short-lived climate forcing factor. Here, the direct effects of BC emissions from India (IDBC) and China (CNBC) are investigated in East Asia during summer using the state-of-the-art regional climate model RegCM4. In summer, IDBC and CNBC account for approximately 30% and 46% of the total BC emissions in Asia, respectively. The total BC column burden from the two countries and corresponding TOA effective radiative forcing are 1.58 mg m(-2) and +1.87 W m(-2) in East Asia, respectively. The regional air temperature increases over 0.3 K at maximum and precipitation decreases 0.028 mm day(-1) on average. Individually, IDBC and CNBC each can bring about rather different effects on regional climate. IDBC can result in a cooling perturbation accompanied by a substantially increased cloud amount and scattering aerosol loading, resulting in a complex response in the regional precipitation, while CNBC can lead to regional warming, and further induce a local flood in northern China or drought in southern China depending on the opposite but significant circulation anomalies. CNBC plays a dominant role in modulating the regional climate over East Asia due to its higher magnitude, wider coverage, and stronger climate feedback. The direct effect of the total BC from both countries is not a linear combination of that of IDBC and CNBC individually, suggesting that the regional climate responses are highly nonlinear to the emission intensity or aerosol loading, which may be greatly related to the influences of the perturbed atmospheric circulations and climate feedback.

The present study examines the aerosol characteristics over Patiala in northwestern India from October 2013 to June 2014. The average mass concentration of the total suspended particulates (TSP) varied from 117 to 301 mu g m(3), with PM10 accounting for similar to 63-83% from October to February (P1) and decreasing to less than similar to 40% from March to June (P2). The aerosol optical depth (AOD(500)) exhibited its highest values during October (0.818) and its lowest during April (0.332), with the wavelength dependence differing significantly on a temporal scale. The Angstrom exponent (alpha(380-870)) values indicated a relatively high quantity of fine-mode particles over the study region during P1 as compared to P2, which is consistent with the PM measurements. The average monthly mass concentration of the climate forcing agent black carbon (BC) varied from 2.4 to 12 mu g m(3), with the highest mass concentration in December and the lowest in June. The average monthly single scattering albedo (SSA(500)) derived from the OPAC (Optical Properties of Aerosols and Clouds) model varied from 0.890 to 0.947, with lower values during P1 than P2. The average monthly clear-sky direct atmospheric aerosol radiative forcing (ATM ARF) estimated by the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model ranged between +12 and +36 Wm(-2) over the study region. Even though the mass fraction of BC averaged over the study period was only 2.4% of the total mass of the composite aerosol, its contribution to net ATM ARF was found to be significant (> 60%), indicating that BC contributes significantly to warming on a regional scale. These results improve our understanding of the impact of BC and composite aerosol on the earth's radiation budget and hence on regional climate.

The measurement of black carbon (BC) and organic carbon (OC), dust in total suspended particulates (TSP) was carried out at Yulong Snow Mountain (Mt. Yulong) and Ganhaizi Basin, in the Mt. Yulong region, southwestern China. TSP samples were analyzed using a thermal/optical reflectance carbon analyzer. Results show that average BC and OC concentrations in TSP in the Mt. Yulong region were 1.61 +/- 1.15 mu g/m(3) and 2.96 +/- 1.59 mu g/m(3), respectively. Statistical results demonstrated that there were significant differences in mean BC and OC contents between Ganhaizi Basin and Mt. Yulong at the 0.05 level. Strong correlations between BC and OC indicate their common dominant emission sources and transport processes. Temporal variations of BC, OC, and optical attenuation (ATN) values were consistent with each other in carbonaceous aerosols. The ratios of OC/BC in monsoon season were significantly higher than in non-monsoon in aerosols from Ganhaizi, which is closely related to the formation of secondary organic carbon (SOC) and extensive motor vehicle emissions from tourism activities. The temporal variations of BC, OC and ATN in carbonaceous aerosols in Ganhaizi and Mt. Yulong were totally different, probably due to elevation difference and diverse tourism activity intensity between the two sites. Time-averaged aerosol optical depth (AOD) at the wavelength of 550 nm in Mt. Yulong was higher than that of the inland of the Tibetan Plateau (TP). Source apportionment indicated that intensive exhaust emissions from tourism vehicles were the main local sources of atmospheric pollutant in the Mt. Yulong region. Biomass-burning emissions released from South Asia could penetrate into the inland of the TP under the transport of summer monsoon. Further study is needed to assess light absorption and radiative forcing of carbonaceous aerosols, and modeling research in combination with long-term in-situ observations of light-absorbing particulates (LAPs) in the TP is also urgently needed in future work.