Quantifying the contributions of various emission sources to black carbon and assessment of control strategies in western China

In this study, an air quality model WRF-Chem (Weather Research and Forecasting Chemistry) was used to simulate meteorological conditions and surface black carbon (BC) concentrations in the western China from June 2016 to May 2017, given emissions from various sources in Asia. Comparison between simulations and measurements in western China showed that the model can capture the key spatial and temporal features of meteorological elements and surface BC concentrations. The modeling framework was then used to quantify the relative contributions of different emission sectors to BC concentrations via sensitivity experiments. Our results show that the residential emission sector presented the largest contribution in western China. The second largest contributor for the highly populated mega-cities (HM) region including Sichuan and Guanzhong basins, and for the remote background (RB) region covering the central part of the Tibetan Plateau (TP), was the industrial sector and the transportation sector, respectively. Power plants and open biomass burning sources played minor roles in the regional BC concentration. The seasonality of BC concentrations showed higher values in winter, mainly due to the residential winter heating under conditions of lower precipitation scavenging and poor boundary layer mixing. A further evaluation of emission control strategies shows that a 50% reduction of residential emissions caused annual mean surface BC concentrations in the RB and HM regions to decrease by 36.2% and 36.7%, respectively. In contrast, a 50% reduction in industrial emissions or transportation emissions led to less than 12% decreases in both regions. The 50% reduction of transportation emissions caused BC concentrations to decrease by 9.2% in the RB region, larger than the 5.9% decrease caused by a 50% reduction of industrial emissions. Transportation emissions were responsible for more BC pollution than industrial emissions for the RB region, in contrast to the highly-industrialized HM region. Therefore, more attention should be paid to transportation emissions when designing control strategies for air pollution over the TP. The results from this work provide useful information for local governments to prepare and implement air pollution guidelines in western China.