Characteristics and Source Analysis of Water-Soluble Inorganic Ions in PM10 in a Typical Mining City, Central China

A total of 61 PM10 samples in Huangshi (HS), Central China, were collected every sixth day from April 2012 to March 2013 and were analyzed for water-soluble inorganic ions (WSIIs) by ion chromatography. The sum of three major ions (SO4, NO3, and NH4) accounted for 75.8% of the total WSIIs on average. The results of a non-parametric test (Kruskal-Wallis) show that, except for Na+ (p > 0.05), the other ions present a distinctly seasonal variation with a statistically significant difference (p < 0.05). The minimum concentrations of all ions were found in summer, while the maximum values presented in autumn (for Ca2+) and winter (for Cl−, NO3, SO4, K+, NH4, Mg2+). Based on the highest ratio of Cl−/Na+ (3.02) and the highest concentration of K (4.37 μg·m−3), Ba (0.37 μg·m−3), and Sr (0.07 μg·m−3) in February 2013, it can be concluded that firework powders have aggravated the haze weather during the Spring Festival of 2013. The micro-equivalent concentrations of cations and anions were calculated and the comparisons between the calculated and measured NH4 concentrations were conducted. The results illustrate that aerosol particles in HS are acidic and there may exist some other cationic ions not detected in this study. An obvious positive correlation and good linear regression among WSIIs suggest that the chemical forms in HS aerosols show a great variety of combinations, such as NH4NO3, NH4HSO4, (NH4)2SO4, NH4Cl, KCl, KNO3, NaCl, NaNO3, Ca(NO3)2, CaSO4, MgCl2, Mg(NO3)2, and MgSO4. The WSIIs have large positive correlation and linear regression with the elements, suggesting that WSIIs in mining cities are strongly influenced by element constituents. Principal component analysis implies that WSIIs in PM10 are probably from three sources. NH4, Mg2+, NO3, K and K+, Cl− and Cl, SO4, and S accounted for 46.9% of the total variances, suggesting likely anthropogenic sources, especially coal combustion, vehicular exhaust, and biomass burning. Mg accounted for 23.3% of the total variances and Ca2+ and Ca explained 18.1% of the total variances, demonstrating that another important source is mineral dust from both natural and anthropogenic sources.