Characteristics Of Water-Soluble Inorganic Ions In Aerosol Particles In Jingjinji-Mega Typical Cities

Aerosol has important effects on climate, environment and human health and water-soluble ions are important chemical composition in aerosol. It is important to study concentration levels, sources and size distributions of water-soluble ions in aerosol. In recent years, with the increasing of energy consumption and the amount of automobile, regional pollution has become more serious in Beijing-Tianjin-Hebei Region. Especially since the haze happened frequently in Beijing-Tianjin-Hebei Region, it is an imminent study about water-soluble ions in aerosol.To investigate the concentration levels, sources and size distributions of water soluble inorganic ions (WSI), size-segregated aerosol samples were collected using Andersen cascade sampler from Aug2010to Aug2011in Beijing, Tianjin, Tangshan and Baoding. The WSI were analyzed by ion chromatography(IC).The results indicated that the order of total WSI (TWSI) concentration of TSP in the region was Tianjin>Baoding>Beijing>Tangshan. The order of TWSI of the fine particles in the region was Baoding>Tianjin>Beijing>Tangshan. The annual mean concentrations of TWSI in the coarse mode were41.36±15.76,48.04±15.79,39.40±11.03,40.49±13.32μg·m-3in Beijing, Tianjin, Tangshan and Baoding, respectively. The annual mean concentrations of TWSI in the fine mode were66.54±47.95,69.12±34.85, 61.80±44.63,71.73±45.12μg·m-3in Beijing, Tianjin, Tangshan and Baoding, respectively. All the annual mean concentrations of TWSIin the fine mode in the four sites had exceeded averaged concentration of PM2.5in the environmental quality standards (35μg·m-3), which indicated that the pollution of TWSI was serious. Secondary water-soluble ions (SWSI)(SO42-, NO3-and NH4+) and Cl-were the main components, and were mainly found in the fine particles in the four sites of Beijing-Tianjin-Hebei Region. In the coarse particles, NO3-、Ca2+and SO42-were the dominant contributions to WSI. Almost all water-soluble ions in fine particles are similar seasonal variation characteristics.The highest WSI concentrations appeared in winter or in summer.Particle size distribution analysis reveals that SO42-、NO3-、Na+and K+showed a bimodal size distribution. The first peak with fine mode appeared at0.43～.1μm, and the second peak with the coarse mode appeared at4.7～5.8μm. NH4+was unimodal the peak with the fine mode of0.43～1.1μm. Ca2+and Mg2+were unimodal the peak respectively with the coarse mode of4.7～5.8μm. Modes of SNA transferred obviously in Beijing-Tianjin-Hebei Region, except Beijing, which may be due to higher humidity. Haze is more conducive to generation and accumulation of water-soluble ions, in which the accumulation of SNA is major.Sources analysis indicated that dust, biomass burning emission, sea salt, secondary formation in fine particles and heterogeneous reaction of NH4+and NO3-in coarse particles were the major sources of TWSI in Beijing-Tianjin-Hebei Region. Secondary formation and dust were the major sources of the fine particles, in which the contributing rate of secondary formation was over40%. Coal burning emission and exhaust pollution in Beijing-Tianjin-Hebei Region becomes more and more serious. The whole area should strengthen the control of gaseous pollutants emissions.