Seasonal Variations and Correlation Analysis of Water-Soluble Inorganic Ions in PM2.5 in Wuhan, 2013

Daily PM2.5 and water-soluble inorganic ions (NH4+, SO42-, NO3-, Cl-, Ca-2(+), Na+, K+, Mg2+) were collected at the Hongshan Air Monitoring Station at the China University of Geosciences (Wuhan) (30 degrees 31'N, 114 degrees 23'E), Wuhan, from 1 January to 30 December 2013. A total of 52 effective PM2.5 samples were collected using medium flow membrane filter samplers, and the anionic and cationic ions were determined by ion chromatography and ICP, respectively. The results showed that the average mass concentration of the eight ions was 40.96 mu g/m(3), which accounted for 62% of the entire mass concentration. In addition, the order of the ion concentrations was SO42- > NO3- > NH4+ > Cl- > K+ > Ca2+ > Na+ > Mg2+. The secondary inorganic species SO42-, NO3- and NH4+ were the major components of water-soluble ions in PM2.5, with a concentration of 92% of the total ions of PM2.5, and the total concentrations of the three ions in the four seasons in descending order as follows: winter, spring, autumn, and summer. NH4+ had a significant correlation with SO42- and NO3-, and the highest correlation coefficients were 0.943 and 0.923 (in winter), while the minimum coefficients were 0.683 and 0.610 (in summer). The main particles were (NH4)(2)SO4 and NH4NO3 in PM2.5. The charge of the water-soluble ions was nearly balanced in PM2.5, and the pertinence coefficients of water-soluble anions and cations were more than 0.9. The highest pertinence coefficients were in the spring (0.9887), and the minimum was in summer (0.9459). That is, there were more complicated ions in PM2.5 in the summer. The mean value of NO3-/SO42- was 0.64, indicating that stationary sources of PM2.(5) had a greater contribution in Wuhan.