Origin of air pollution during a weekly heavy haze episode in Hangzhou, China

Air pollution has recently become China's highest environmental issue due to the rapid development of industry and urbanization. So far, the precise sources of air pollution of main cities are unknown. To identify sources, we studied air pollution in the Hangzhou city from November 25 to December 11, 2013, at eight monitoring stations. We analyzed PM2.5, PM10, O-3, NO2, CO, SO2, and satellite observations for aerosol optical thickness (PM: particulate matter). Pollution sources were identified by trajectory clustering and receptor models. The results show that during the weekly heavy haze episode, December 3-9, mean concentrations were 293.4 +/- 103.2 mu g m(-3) for PM2.5, 376.8 +/- 119.4 mu g m(-3) for PM10, 58.0 +/- 37.2 mu g m(-3) for SO2, 118.5 +/- 39.3 mu g m(-3) for NO2, and 2,429 +/- 740 mu g m(-3) for CO. The back trajectory cluster analysis indicates that the predominant clusters are south (37.1 %) and southeast (28.6 %) during the weekly heavy haze episode. The results of the receptor models show that the sources affecting formation of the extremely high PM2.5 in Hangzhou are mainly located in the southeastern coast of Zhejiang and Fujian provinces, north part of Jiangxi, and central part of Jiangsu province. Rather than local emissions, it is also found that air mass pathways and cross-border transports control high PM2.5 concentrations and formation in Hangzhou. Therefore, it is necessary to implement air pollution control for all industrial areas at local, regional, and national scales in China.