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

Abstract

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+, Mg2+, K+, Ca2+, NH4+, Cl−, SO42− and NO3−) were 75.5±52.9μg/m3 in spring, 26.5±12.3μg/m3 in summer, 22.7±20.4μg/m3 in autumn, and 31.1±23.9μg/m3 in winter, respectively. The secondary ions (NO3−, SO42− and NH4+), 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 NH4+ and SO42− (r=0.95, p<0.01) as well as NH4+ and NO3− (r=0.90, p<0.01) in fine particles; while in coarse particles, correlations between Mg2+ and NO3− (r=0.80, p<0.01), and Ca2+ and NO3− (r=0.85, p<0.01) were found. The concentrations of Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3−, and SO42− were 2.02, 0.81, 0.36, 1.65, 9.58, 4.01, 18.9, and 18.4μg/m3 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.