Characteristics of mass and chemical species size distributions of particulate matter during haze pollution in the winter in Beijing

To investigate characteristics of chemical species and their size distributions of particulate matters (PM) during the haze events, the PM samples were collected by a Dekati low pressure impactor during the winter haze/fog events in Beijing. The concentrations of water-soluble ions, and organic and elemental carbon were quantified. The PM mass concentrations under different weather conditions were compared. The ratio of PM_2.5/PM₁₀ was over 74% in all weather conditions, implying that fine particles predominated over the severe haze pollution. SO₄^2-, NO₃^-, NH₄⁺, Cl^-, and Ca²⁺ were the most abundant water-soluble ions. Distinct size distributions were found for different ions. SO₄^2-, NO₃^-, and NH₄⁺ peaked at 0.76 μm. Ca²⁺ and Mg²⁺ both peaked at 0.31 μm and 5.13~8.09 μm, but were mainly in the coarse mode. Cl^- and K⁺ both peaked at 0.76 μm and 5.13 μm, but were mainly in the fine mode. OM and EC also dominated in the fine mode. The concentrations of secondary inorganic ions and carbonaceous matters increased apparently during haze pollution. Meanwhile, SOR, NOR, and OC/EC were higher during the haze events, suggesting that the formation of secondary inorganic and organic aerosols played a dominant role for haze pollution. During the haze extention period, the contribution of primary emissions from vehicle exhaust increased. For submicron aerosols, the contribution from mobile sources was greater than stationary sources based on the analysis of the size distributions for the ratio of NO₃^- to SO₄^2- concentrations. Regional transport of coal-burning pollutants played a significant role in the formation of heavy pollution, while dust had small effects.