Characteristics of PM2.5 in Miyun, the northeastern suburb of Beijing: chemical composition and evaluation of health risk

In recent years, the fine particulate matter pollution has become increasingly serious in Beijing, the capital of China. Being considered as an environment-friendly district of Beijing, current research concerning air pollution in Miyun area was relatively less. From August 24, 2013 to September 29, 2013, 24-h samples were collected in the urban and rural areas of Miyun, Beijing, so as to better understand the sources contributing to PM2.5 and the risk to human health in this district. The data obtained showed that daily PM2.5 mass concentrations ranged from 35.33 to 318.71 mu g m(-3) in the urban sampling site, which however were between 12.62 and 292.33 mu g m(-3) in the rural sampling site. At least 23.5 and 41.2 % of the monitoring data, respectively, exceeded the limit value. The mass concentrations of a number of PM2.5 elements fluctuated significantly in the decreasing order of Zn, Ba, Sr, Cu, Pb, Cr, V, Ni, Sb, and Cd. The daily contribution of three cations (NH4 (+), K+, and Na+) and four anions (F-, Cl-, NO3 (-), and SO4 (2-)) to PM2.5 mass simultaneously varied from 27.51 to 44.04 % and from 29.54 to 46.14 %. In addition, significant linear correlations between main constituents of the ions (SO4 (2-), NO3 (-), and NH4 (+)) at both sites indicated that the majority of NH4 (+) was probably in the form of ammonium sulfate and ammonium nitrate. The risk levels of carcinogenic heavy metals detected in survey region occurred in the order of Cr, Cd, and Ni, of which, Cr may have a potential risk to the environment. High risk levels of both carcinogenic and non-carcinogenic heavy metals were easy to occur on haze-fog days.