The influence of the black carbon warming effect on near-surface ozone in China in summer

Black carbon aerosol (BC) has significant impacts on regional climate changes due to its absorption of solar radiation, which might lead to substantial variations in surface ozone (O3) pollution. Therefore, the potential role of the BC warming effect on O3 responses during summertime in China is investigated and quantified based on online-coupled regional climate-chemistry model (RegCM-Chem) simulations and multiple linear regression (MLR) analysis. The results suggest that the absorption of solar radiation can lead to considerable decreases in cloud amount, precipitation and relative humidity in most regions of China in summer, which further cause a warming of the low-layer atmosphere and an enhancement in the southerly East Asian summer monsoon. The variations in O3 concentrations in response to the BC warming effect are almost as large as the observed O3 growth in China from 2013 to 2017 (7.2%). They have significant regional specificity over China. Due to the warming effect of BC, the near-surface daily O3 concentrations are increased in most areas of Central to East China, with an increase of 6.2%, while they are decreased in Southwest China, with a reduction exceeding 5.8%, implying that BC emission reductions favor the mitigation of ozone pollution in East China in summer. Further investigations via MLR analysis indicate that the BC-induced O3 increases in Central and East China and O3 decreases in Southwest China are strongly related to changes in relative humidity, while the BC-induced O3 increases in North and Northeast China are likely linked to the changes in transportation. These results may help us better understand the mechanism of O3 variation and can provide a scientific reference for BC and O3 reduction strategies over China.