Characteristics and sources apportionment of water-soluble ions in PM2.5 of Xiamen City, China

The PM2.5 samples were synchronously collected in urban and suburban areas of Xiamen city during August and December in 2014 to investigate the characteristics and sources of water-soluble ions in atmospheric PM2.5. Nine water-soluble ions (F-, Cl-, NO3-, SO42-, Na+, K+, NH4+, Ca2+, Mg2+) were determined by ion chromatography. The level of water-soluble ions in PM2.5 of Xiamen city was relatively lower, and the sum concentrations (μg/m3) of total water-soluble ions showed the order of urban area in winter (18.16) > suburban area in winter (14.55) > suburban area in summer (6.87) > urban area in summer (5.33). Precipitation had a significant effect on the removal of water-soluble ions in PM2.5. Anions in PM2.5 were relative loss in summer, whereas opposite in winter. SO42-, NO3-, NH4+ (SNA) were the major components of water-soluble ions in PM2.5 with a contribution of more than 79.64% to total water-soluble ions, suggesting that the level of secondary ions was relatively high. Correlation analysis and SNA triangular diagram showed that NH4+ in PM2.5 mostly coexisted in the form of (NH4)2SO4 followed by NH4NO3 and alkaline free NH4+ in summer, while mostly in the form of (NH4)2SO4 and NH4NO3 followed by NH4Cl in winter. The mass ratio of N/S demonstrated that the main source to the water-soluble ions in PM2.5 of Xiamen city was coal combustion in summer, while the traffic emissions in winter. Overall, the water-soluble ions in PM2.5 of Xiamen city presented the composite pollution characteristics of traffic source and coal combustion, but barely influenced by marine source. Principal component analysis further indicated that the water-soluble ions in PM2.5 of Xiamen city mainly came from coal combustion, traffic emission and biomass burning. © 2016, Editorial Board of China Environmental Science. All right reserved.