[Chemical composition and mass closure of particulate matter in Beijing, Tianjin and Hebei megacities, Northern China].

To seek an efficient prevention and control method of regional atmospheric pollution in Jingjinji area, mass concentrations and size-resolved chemical composition of particulate matter were investigated at four urban sites and one background site from June 2009 to May 2010. The results show that the annual mean concentration of PM10 was 124, 141, 151 and 183 microg x m(-3) in Beijing, Tianjin, Tangshan and Baoding respectively, while the corresponding percentage of daily limit value exceedances was 29%, 36%, 39% and 52%, which is well above the maximum allowed limit of 150 microg x m(-3) (National Air Quality Stand II). As for PM2.5, the annual average concentration was 55, 68, 79 and 116 microg x m(-3) in Beijing, Tianjin, Tangshan and Baoding, which is higher than that in the background site with a factor of 1.5, 1.9, 2.2 and 3.2, respectively, while the corresponding proportion of daily exceedances of 75 microg x m(-3) (WHO IT-1) was 29%, 33%, 42% and 65%. Seasonal variations of PM2.5 and PM10 concentration were significant at the urban sites with the highest value being measured in winter. In order to reconstruct the particle mass, the determined components were classified into five groups as follows: secondary inorganic aerosol, sea salt, heavy metal, mineral matter and construction dust. The urban-sites-averaged contribution of these components to PM2.1 was 28.5%, 5.8%, 1.8%, 14.8% and 3.8%, whereas that to PM2.1-9 was 11.3%, 6.7%, 1.1%, 43.5% and 7.6%, respectively. The particle pollution was very severe in Baoding with the major component of secondary inorganic aerosol and mineral matter in PM2.1 and PM2.1-9, respectively. The estimated contribution of anthropogenic sources to PM2.1 in Beijing was larger than that of natural sources with a factor of 3.5 whereas the ratio of anthropogenic sources to natural ones was 0.6 for PM2.1-9. The contribution of secondary components to PM2.1 was equivalent to primary emissions, which suggests the precursors emitted from coal combustion and vehicle exhaust should be controlled in the target area. In contrast, the ratio of primary emissions to secondary particulate matters in PM2.1-9 was up to 5, indicating measures are required to reduce dust from construction areas. Finally, the reduction of human health-related heavy metals is also necessary despite its minor contribution to particles.