Characterizations of PM2.5 Pollution Pathways and Sources Analysis in Four Large Cities in China

Particulate matter with an aerodynamic diameter of 2.5 micrometers or less (PM2.5) is a primary pollutant in most cities in China. PM2.5 poses a significant human health risk, especially in the most densely populated urban areas. We used observations of PM2.5 and backward air mass trajectories modeled by HYSPLIT-4. We characterize how air movement patterns influence pollution levels in four large cities of China. Then we developed a method to evaluate regional and local sources and contributions of PM2.5. For Beijing and Shanghai, PM2.5 concentrations are sensitive to air moving direction, indicating significant influence of air movement on PM2.5 pollution. In Beijing, PM2.5 concentrations were higher when the air masses were from the south and the east. In Shanghai, pollution was greater with northerly air mass flows. Regional contributions of PM2.5 in Beijing during 2013 were 46, 62, 52, and 39% in spring, summer, autumn and winter, respectively. In Shanghai, regional contributions over four seasons were 36, 39, 45, and 35%. In Guangzhou and Chengdu, PM2.5 concentrations were more sensitive to speed rather than direction of air mass movements, indicating weaker pollution pathways. In Guangzhou, regional contributions were smaller over the four seasons: 15, 28, 16, and 22% while in Chengdu, they are 21, 52, 28, and 14%. These results are comparable to previous results obtained using complex atmospheric chemical transport models.