Changes in source contributions of particulate matter during COVID-19 pandemic in the Yangtze River Delta, China

Abstract. Within a short time after the outbreak of coronavirus disease 2019 (COVID-19) in Wuhan, Hubei, the Chinese government took a nationwide lockdown to prevent the spread of the pandemic. The quarantine measures have significantly decreased the anthropogenic activities, and thus improving the air quality. To study the impacts caused by the lockdown on specific source sectors and regions in the Yangtze River Delta (YRD), the Community Multiscale Air Quality (CMAQ) model was used to investigate the changes in source contributions to fine particulate matter (PM2.5) from January 23 to February 28, 2020, based on different emission control cases. Compared to Case 1 (without emission reductions), the total PM2.5 mass for Case 2 (with emission reductions) decreased by larger than 20 % over the entire YRD and the reduction ratios of its components were 15 %, 16 %, 20 %, 43 %, 34 %, and 35 % in primary organic aerosol (POA), elemental carbon (EC), sulfate, nitrate, ammonium, and secondary organic aerosol (SOA), respectively. The source appointment results showed that PM2.5 concentrations from transportation decreased by 40 % while from residential and power decreased by less than 10 % due to the lockdown. Although all sources decreased, the relative contribution changed differently. Contributions of residential increased by more than 10 % to 35 %, while that of the industry decreased to 33 %. Considering the regional transport, the total PM2.5 mass of all regions decreased 20–30 % in the YRD with the largest decreased value of 5.0 μg m−3 in Henan, Hebei, Beijing, and Tianjin (Ha-BTH). In Shanghai, the lower contributions from local emissions and regional transmission (mainly Shandong and Ha-BTH) led to the reduced PM2.5. This study suggested adjustments of control measures for various sources and regions. Also, it was necessary to strengthen the regional collaboration at a large scale to improve the air quality in the YRD.