Chemical composition and size distribution of airborne particulate matters in Beijing during the 2008 Olympics

Size-segregated aerosol samples were collected daily in Beijing from 1 Jun. to 20 Sep. during the Beijing Olympic Games in 2008 to investigate aerosol concentrations, particle size distributions, and sources as well as the effects of pollution control measures on the chemical compositions (including Water-soluble ions, trace elements, elemental carbon (EC), and organic carbon (OC)) in aerosols of different sizes. Water-soluble ions, EC, OC, and trace elements accounted for 45.0%, 1.6%, 14.7%, and 11.4% of the total particle mass (PM), respectively. Approximately 56%, 56%, 30%, 71% and 55% of the PM, water-soluble ions, trace elements, EC and OC, respectively, were associated with particles smaller than 2.1 μm. Sulfate, nitrate, and ammonium were the dominant ions, which together accounted for approximately 77% of total water-soluble ions. The crustal elements accounted for the majority of the trace elements present. Different sources showed different mass size distributions. Anthropogenic source compounds, such as sulfate, nitrate, ammonium, OC, EC, and toxic elements, were mainly present in fine mode aerosols, whereas crustal elements, such as Al, Fe, Ca, Mg and Ba, primarily occurred in the coarse mode. SO₄ ²⁻ and NH₄ ⁺ concentrations were strongly correlated (r² = 0.90, slope = 1.63) in the fine mode, thereby indicating that SO₄ ²⁻ was mainly present as (NH₄)₂SO₄; in contrast, a weak correlation between SO₄ ²⁻ and NH₄ ⁺ (r² = 0.18, slope = 0.54) was observed in the coarse mode, indicating that SO₄ ²⁻ was associated with other ions. Similarly, SO₄ ²⁻ and NO₃ ⁻ exhibited a stronger correlation in the fine mode than in the coarse mode, indicating that SO₄ ²⁻ and NO₃ ⁻ were formed via the same in-cloud processes in fine particles. The OC/EC ratio and the correlations between EC and OC concentrations showed that the sources of carbonaceous species were secondary organic carbon from fine particles and the long-range transport of coarse carbonaceous particles from biomass burning. The concentrations of atmospheric pollutants declined during the 2008 Olympic Games, indicating that the pollution control measures were effective in decreasing particulate air pollution in Beijing.