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Abstract Ambient PM2.5 samples were collected simultaneously at 8monitoring sites (Dingling, Chegongzhuang, Shijingshan, Dongsi, Tongzhou, Liangxiang, Yizhuang and Yufa) in Beijing, from August 2012 to July 2013. And positive matrix factorization (PMF) was used to identify the sources of PM2.5 based on ambient PM2.5 compositional data including concentrations of organic carbon (OC), elemental carbon (EC), ions and metal elements. Results from PMF indicated that the six major sources of ambient PM2.5 were secondary sources, coal combustion, soil dust, vehicle emission, industrial sources and construction dust, with an annual average contribution of 42%, 19%, 19%, 10%, 6% and 4%, respectively. The contributions of the sources to PM2.5 in Beijing showed significant seasonal variations. Soil dust was the primary source in spring because of the highest frequency of windy weather. Secondary sources became the major contributor in summer, autumn and winter, and even covered 56% in summer. Coal combustion exhibited increased contributions in winter with values of 25%. The contributions of the PM2.5 sources also showed some spatial differences. Coal combustion showed significantly higher contributions in suburban areas than in urban areas ,whereas the secondary sources were regional. And the secondary sources were dominated during the cumulative pollution events, accounting for more than 50% of the PM2.5 mass. Strengthening the controls of gaseous precursors (NOx, SO2 and VOCs) was of great significance for the reduction of PM2.5 in Beijing .
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Received: 12 March 2015
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