The Deposition Characteristic And Effect Factors Of PM_2.5 Water Soluble Inorganic Ions Above Forest In Beijing

In recent years, PM2,5 has become to be the major pollutant in atmosphere. Research showed that thought plants could help decrease the PM2.5, while there were rare study about the effect on the concentration of PM2.5 water soluble ions fractions and the deposition velocity by forest in China. In this study, we set four sampling sites:the Olympic Forest Park, Jiufeng National Forest Park, the lawn in campus and the gate of Beijing Forestry University. We got the samplings at the same time in these four sites during March to December in 2013 for analysis. We measured eight typical kinds of PM2.5 water soluble inorganic ions:Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3- and SO42-. The gradient technique also was used to measure the deposition velocity of water soluble inorganic ions. The result is as follow:(1) The total concentration of PM2.5 water soluble ions in the horizontal direction was gate (54.736 μg/m3)> lawn (45.021 μg/m3)> Olympic (38.100 μg/m3)> Jiufeng (30.809 μg/m3). The concentration ratio of SO42- and NO3- account for over 50% of the total water soluble ions. The concentration in four seasons was that winter> spring> autumn> summer, except NH4+, its biggest concentration in spring, the concentration of Ca2+ and Mg2+ were higher in summer. In Olympic and Jiufeng, the concentration regularity in vertical height showed the follow variation pattern the concentration over tower> the concentration in the middle of tower> the concentration under tower.(2) We calculated the deposition velocity of PM2.5 water soluble ions in spring, summer and autumn in Olympic Forest Park and Jiufeng Forest Park by gradient technique. It showed that the deposition velocity of summer was bigger than spring and autumn, and it was bigger at daytime than nighttime. According to the deposition velocities of PM2.5 water soluble inorganic ions was 0.26cm/s in the Olympic park, and the deposition velocity was 0.38 cm/s in Jiufeng National Forest Park. If based on the results from Olympic calculation, the annual forest canopy layer stranded 5.78×108 g/y PM2.5 water soluble inorganic ions; based on the results from Jiufeng calculation, the annual forest canopy layer stranded 6.83 × 108 g/y PM2.5 water soluble inorganic ions. Therefore, to improve the air quality in Beijing and control fine particles pollution, trees play an extremely important role.