PM_(10), PM_(2.1) and associated water-soluble inorganic ions at urban and suburban sites in Nanjing, China

摘要

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 ((NO_2)~-, F~-, (NO_3)~-, Cl~-, (SO_4)~(2-), (NH_4)~+, Mg~(2+), Ca~(2+), Na~+, K~+) were measured for all the samples. At suburban site, the seasonal variation of PM_(10) was spring>fall>winter>summer, while PM_(2.1) was winter>fall>spring>summer. The mass concentration of PM_(10) was highest in spring; however, the ratio of PM_(2.1)/PM_(10) 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, (SO_4)~(2-), (NO_3)~-, and (NH_4)~+, 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 PM_(10) and PM_(2.1), respectively. The ratios of (NO_3)~-/(SO_4)~(2-) were smaller than 1 suggesting that stationary source emissions were more important than the vehicle emissions in summer. (NO_3)~-, (SO_4)~(2-) and (NH_4)~+ showed good correlations between each other both in PM_(10) and PM_(2.1), and they were in form of NH_4NO_3 and (NH_4)_2SO_4 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.