Chemical characterization and source analysis of water-soluble inorganic ions in PM2.5 from a plateau city of Kunming at different seasons

Water-soluble inorganic ions (WSIIs) in PM_2.5 from different cities have been studied in previous studies. However, the studies of WSIIs in plateau cities are relative deficient. Due to differences in topography, climate and emission sources, the WSIIs characteristics of plateau cities are expected to be different. Here, we determined the concentrations of WSIIs (SO₄^2-, NO₃^-, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺, F^-, Cl^-, NO₂^-) in PM_2.5 from different seasons of Kunming, a typical plateau city in southwest China. The data will improve our understanding of the chemical characterization and source of PM_2.5 in plateau environment. Our results showed that the secondary aerosols were the main pollutants (contributing >50% to PM_2.5) in PM_2.5 of Kunming, which mainly from coal combustion, agricultural activities and vehicle exhaust. Seasonally, high volatility of the NO₃^- and NH₄⁺ and washout effects of rainfall in hot months (wet seasons) were favorable for the decreased of pollutants, while high emission, poor dispersion conditions and low removal rate could lead to the increased of pollutants in cold months (dry seasons). It suggested that adequate NH₃ and intense solar radiation promotes the photochemical reactions of SO₂, NO_x and NH₃ to form NH₄HSO₄, (NH₄)₂SO₄ and NH₄NO₃. High temperature in hot months would promote the volatilization of NH₄NO₃ in Kunming.