Size-resolved aerosol water-soluble ions at a regional background station of Beijing, Tianjin, and Hebei, North China.

The characteristics of water-soluble ions in size-resolved particulate matter were investigated using ion chromatography at Shangdianzi, a regional background station of Beijing, Tianjin, and Hebei. Seasonal total concentrations of ions (Na, Mg, K, Ca, NH, Cl, SO and NO) were 75.5±52.9μg/m in spring, 26.5±12.3μg/m in summer, 22.7±20.4μg/m in autumn, and 31.1±23.9μg/m in winter, respectively. The secondary ions (NO, SO and NH), mainly associated with fine particles, accounted for 84.2% in spring, 82.1% in summer, 81.5% in autumn and 76.3% in winter of all ions. Strong correlations were found between NH and SO (r=0.95, p<0.01) as well as NH and NO (r=0.90, p<0.01) in fine particles; while in coarse particles, correlations between Mg and NO (r=0.80, p<0.01), and Ca and NO (r=0.85, p<0.01) were found. The concentrations of Na, K, Mg, Ca, NH, Cl, NO, and SO were 2.02, 0.81, 0.36, 1.65, 9.58, 4.01, 18.9, and 18.4μg/m in particulate matter from southeast-derived air masses, which were typically 1.58-3.37 times higher than in northwest trajectories. Thus, concentrations of water-soluble ions at this background station were heavily influenced by regional transport of serious pollution derived from biomass burning, coal combustion, industrial and vehicle exhaust emissions from Beijing, Tianjin, and Hebei.