Spatio-temporal distribution and chemical composition of PM2.5 in Changsha, China

The rapid economic development and significant expansion of urban agglomerations in China have resulted in issues associated with haze and photochemical smog. Central China, a transitional zone connecting the eastern coast and western interior, suffers from increasing atmospheric pollution. This study performed a spatio-temporal analysis of fine particulate matter (PM2.5) pollution in Changsha, a provincial capital located in central China. Samples of PM2.5 were collected at five different functional areas from September 2013 to August 2014. The PM2.5 concentration at the five sampling sites was the highest in winter and the lowest in summer, with an average annual PM2.5 concentration of 105.2 ± 11.0 μg/m3. On average, residential sites had the highest concentrations of PM2.5 while suburban sites had the lowest. We found that inorganic ionic species were dominant (~48%), organic species occupied approximately 25%, whereas EC (~3.7%) contributed insignificantly to the total PM2.5 mass. Ion balance calculations show that the PM2.5 samples at all sites were acidic, with increased acidity in spring and summer compared with autumn and winter. Air quality in Changsha is controlled by four major air masses: (1) Wuhan and the surrounding urban clusters, (2) the Changsha-Zhuzhou-Xiangtan urban agglomeration and the surrounding cities, and (3) southern and (4) eastern directions. The north–south transport channel is the most significant air mass trajectory in Changsha and has a significant impact on PM2.5 pollution.