Chemical characteristics of PM2.5 species in Beijing ambient air

This paper describes the PM2.5 (participate matter with aerodynamic diameters less than 2.5 μm) concentration and composition in the ambient air of Beijing. Weekly samples were simultaneously collected for one year at the Chegongzhuang and Qinghuayuan sites in Beijing. The PM2.5 compositions at the two sampling sites were similar. The principal components were carbonaceous species and water-soluble ions, with their total mass accounting for more than 50% of the total PM2.5 mass. Organic carbon (OC) and elemental carbon (EC) exhibited the same seasonal variations as PM2.5, i.e. the highest mass concentrations occurred in the winter while the lowest in the summer. The lowest nitrate levels were in the summer with nearly 50% of the nitrate volatiles coming from Teflon filters. Sulfates and crustal-related species showed quite different seasonal trends from those of PM2.5, suggesting that the sulfate levels were mainly determined by the SO2 gas to sulfate transformation rate, while the crustal-related species were strongly impacted by the frequent dust storms in the spring, resulting in severely elevated concentrations from winter to spring.