PM10, PM2.1 and associated water-soluble inorganic ions at urban and suburban sites in Nanjing, China

Airborne particles, especially particle size smaller than 10μm, samples were collected at two sites in Nanjing from October 2009 to August 2010. The mass concentrations of ten water-soluble ions (NO₂^-, F^-, NO₃^-, Cl^-, SO₄²⁺, NH₄⁺, Mg²⁺, Ca²⁺, Na⁺, K⁺) were measured for all the samples. At suburban site, the seasonal variation of PM₁₀ was spring>;fall>;winter>;summer, while PM_2.1 was winter>;fall>;spring>;summer. The mass concentration of PM₁₀ was highest in spring; however, the ratio of PM_2.1/PM₁₀ was the lowest. In summer, PM_2.1 pollution can not be ignored. Compared with urban site, the concentration of particles was higher at suburban site, which likely due to be under the influence of industrial zone. In summer, SO₄^2-, NO₃^-, and NH₄⁺, secondary formed compounds, were major ions, totally accounting for 29.51% and 47.45% at urban site, 37.63% and 49.04% at suburban site in PM₁₀ and PM_2.1, respectively. The ratios of NO₃^-/SO₄^2- were smaller than 1 suggesting that stationary source emissions were more important than the vehicle emissions in summer. NO_3-, SO₄^2- and NH₄⁺ showed good correlations between each other both in PM₁₀ and PM_2.1, and they were in form of NH₄NO₃ and (NH₄)₂SO₄ in particles. As a tracer ion of biomass burning, the mass concentration of K⁺ was not ignored in Nanjing, which is much higher in suburban area. Furthermore, K⁺ had good correlations with other ions, indicating that burning activities of crop aggravated the air - - quality.