Characteristics of Water-soluble Inorganic Ions in Atmospheric Aerosols in Shenyang

Abstract

To investigate the levels and seasonal variation of water soluble inorganic components in ambient aerosol in Shenyang, 25 samples were collected with Andersen cascade sampler from Jun. 2012 to May. 2013 and nine water-soluble ions in samples were analyzed by IC. The different characteristics of aerosols between clean and pollution days in winter were discussed based on these samples. The results showed that the annual concentrations of total water soluble inorganic ions were 22.30 μg·m^-3 and 14.29 μg·m^-3 in fine and coarse particles, and SO4^2- and Ca²⁺ were the most abundant ions, respectively. The ratio of mass concentration between SO4^2- and NO3^- was 2.28 and the NH4⁺ existed in the form of (NH4)2SO4 and NH4NO3 in fine particles. The concentrations of total water soluble ions in fine particles were higher in winter and spring compared with those in summer and autumn, and they varied significantly between different seasons. The fossil fuel consumption led to the maximum values of secondary inorganic ions in fine particles during winter. The concentrations of total water soluble ions in coarse particles varied slightly though they were higher in autumn and lower in winter, and the wind-drifting sand was responsible for the higher concentration of Ca²⁺ in autumn in coarse particles. The concentration of SO4^2-, NO3^-, NH4⁺ accounted for 80% of total water soluble inorganic ions during clean days and rose to 94% during pollution days. The ions were mostly concentrated in the size ranges of 0.43-0.65 μm and 0.43-2.1 μm respectively during clean and pollution days in fine mode. The peaks of SO4^2-, NO3^-, NH4⁺ in fine mode shifted from 0.43-0.65 μm to 1.1-2.1 μm, which meant these ions were transformed from condensing mode to droplets mode during pollution days. The air mass produced at Lake Baikal and transported through high altitude to the sampling point caused clean days, however the air mass transported through industrial areas might bring pollutions to the sampling point then caused pollution days.