Aerosol transport pathways and source attribution in China during the COVID-19 outbreak

Abstract. Due to the coronavirus disease 2019 (COVID-19) pandemic, human activities and industrial productions were strictly restricted during January–March 2020 in China. Despite the fact that anthropogenic aerosol emissions largely decreased, haze events still occurred. Characterization of aerosol transport pathways and attribution of aerosol sources from specific regions are beneficial to the air quality and pandemic control strategies. This study establishes source-receptor relationships in various regions of China during the COVID-19 outbreak based on the Community Atmosphere Model version 5 with Explicit Aerosol Source Tagging (CAM5-EAST). Our analysis shows that PM2.5 burden over the North China Plain between January 30 and February 19 is largely contributed by local emissions (40–66 %). For other regions in China, PM2.5 burden is largely contributed from non-local sources. During the polluted days of COVID-19 outbreak, local emissions within North China Plain and Eastern China, respectively, contribute 66 % and 87 % to the increase in surface PM2.5 concentrations. This is associated with the anomalous mid-tropospheric high pressure at the location of climatological East Asia trough and the consequently weakened winds in the lower troposphere, leading to the local aerosol accumulation. The emissions outside China, especially from South and Southeast Asia, contribute over 50 % to the increase in PM2.5 concentration in Southwestern China through transboundary transport during the polluted day. As the reduction in emissions in the near future, aerosols from long-range transport together with unfavorable meteorological conditions are increasingly important to regional air quality and need to be taken into account in clean air plans.