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

ABSTRACT

Particulate matter with an aerodynamic diameter of 2.5 micrometers or less (PM_2.5) is a primary pollutant in most cities in China. PM_2.5 poses a significant human health risk, especially in the most densely populated urban areas. We used observations of PM_2.5 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 PM_2.5. For Beijing and Shanghai, PM_2.5 concentrations are sensitive to air moving direction, indicating significant influence of air movement on PM_2.5 pollution. In Beijing, PM_2.5 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 PM_2.5 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, PM_2.5 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.