Semi-continuous measurement of water-soluble ions in PM2.5 in Jinan, China: Temporal variations and source apportionments

To better understand secondary aerosol pollution and potential source regions, semi-continuous measurement of water-soluble ions in PM2.5 was performed from December 2007 to October 2008 in Jinan, the capital of Shandong Province. The data was analyzed with the aid of backward trajectory cluster analysis in conjunction with redistributed concentration field (RCF) model and principal component analysis (PCA). SO 4 2 − , NO 3 − and NH 4 + were the most abundant ionic species with annual mean concentrations (±standard deviations) of 38.33 (±26.20), 15.77 (±12.06) and 21.26 (±16.28) μg m−3, respectively, which are among the highest levels reported in the literatures in the world. Well-defined seasonal and diurnal patterns of SO 4 2 − , NO 3 − and NH 4 + were observed. The fine sulfate and nitrate oxidation ratios (SOR and NOR) were much higher in summer (SOR: 0.47 ± 0.13; NOR: 0.28 ± 0.03) than those in other seasons (SOR: 0.17–0.30; NOR: 0.12–0.14), indicating more extensive formations of SO 4 2 − and NO 3 − in summer. The most frequent air masses connected with high concentrations of SO 4 2 − , NO 3 − and NH 4 + originated from Shandong Province in spring, autumn and winter, while from the Yellow Sea in summer, and then slowly traveled in Shandong Province to Jinan. RCF model indicated that Shandong Province was the main potential source region for SO 4 2 − and NO 3 − and other potential source regions were also identified including the provinces of Hebei, Henan, Anhui and Jiangsu and the Yellow Sea. Principal component analysis indicated that the major sources contributing to PM2.5 pollution were secondary aerosols, coal/biomass burnings and traffic emissions.