The direct effects of black carbon aerosols from different source sectors in East Asia in summer

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.