| Along with our country industrialization and urbanization advancing, human activities makes the atmospheric dust pollution problems become increasingly prominent in the city region. While the city within the scope of the dry, wet deposition of atmospheric dust fall, the pollution that they generate is not confined to the atmospheric environment, at the same time,it is an important source of pollution to a city of surface runoff. The study of atmospheric dust pollution are very important for the improvement of city environment air quality and surface water environment quality. We select Xi’an urban atmosphere in different function areas to study dust pollution characteristics and ecological risk, in order to reveal the regional dust pollution and the variation characteristics of atmospheric dust, proven the contribution of dust fall on city road runoff pollution,and to provide scientific basis of making the atmospheric environment and water environment protection measures and pollution prevention measures.The main conclusions and results are as follows:Through the acquisition of perennial accumulation atmospheric disposition in Xi’an, we considered the pollution characteristics of atmospheric dust fall, the speciation of heavy metals and their biological effectiveness, ecological risk assessment of atmospheric dust fall and the heavy metal sources,we get the following conclusion:(1) The mass concentration of total COD、deliquescent COD、inorganic nitrogen and heavy metal which are in atmospheric disposition of Xi’an is varies a lot, and in the spatial distribution is extremely uneven. Except COD, with the clean degree of functional areas,the degree of pollution they were weakening. Inorganic nitrogen in the dust is mainly composed of ammonia nitrogen and nitrate nitrogen in these two kinds of morphology, the ratio of ammonia nitrogen and nitrate nitrogen is generally more than 2; The concentrations of Cu, Pb,Zn which are called urban element are highest in industrial area, Ni and Cd elements are mainly concentrated in the industrial, commercial, residential and educational district area and there is little change in those areas, most areas of Xi’an city is suffer from Cd pollution.(2) Pb, Cr and Ni in dust mainly in residual form, the metal is relatively stable. Cu mainly in residual fraction and oxidizable fraction, Zn mainly in residual fraction and acid soluble, the proportion of Cd which is in acid soluble state is higher in dust fall. The biological validity coefficients calculated by the biological validity coefficients K, Zn and Cd were higher than 0.2, this means the transferable part and the bioavailable fraction is higher,has a greater impact on the environment.(3) Cu, Zn, Cr and Ni ecological risk index was smaller in atmosphere dust of Xi’an city,the ecological risk level is low; secondly, Pb and As ecological risk level is medium;ecological risk index of Cd which is the most serious ecological harm is much higher than other heavy metals. From the computational results we can also conclude that the enrichment factor, Cd in various functional areas were greater than 20, the highest among all the heavy metals, it has strong enrichment degree. The enrichment factor of Pb and Zn between 4-10,significantly enriched.(4) By the principal component analysis, Cu, Fe, Cr and Zn elements may be derived from metal smelting, machinery manufacturing, automobile exhaust and tires, engines and other mechanical wear; Cd, Pb and As are the coal and industrial production factor contribution; Al, Ca, Ni come from the crust soil and dust, belonging to the natural source.Through the acquisition of the whole year of the atmospheric dust samples, the amount of dust on the space-time differentiation characteristics of atmospheric dust fall pollution and differentiation characteristics were carefully discussed, obtained the following conclusions:(1) The dust fall amount of each functional area of Xi’an City in winter and spring season exceed the standard seriously; compared to the reference standard,the dust increment in summer and autumn is also large. The dustfall flux have significant differences in different seasons, showing in general: Winter > autumn > spring > summer. And dust fall in different function areas also has significant difference, the overall point of view, the amount of dustfall variation in functional areas: Industrial Zone>commercial zone > residential area > tourist area.(2) There is obvious seasonal differences in concentrations of various forms of nitrogen in dust fall of Xi’an city. The nitrate concentration of ammonia nitrogen in winter is the highest, while for the addition of ammonia is not too obvious. The concentrations of heavy metals in the atmospheric dust of the difference in the four quarter is obviously, mainly showed that in winter and spring is high, and in summer and autumn is low. From the perspective of quality throughout the year, the level of some heavy metals differ greatly in the four seasons. There are obvious differences in different functional areas of each form of nitrogen concentration in Xi’an City, and in different seasons showed similar distribution characteristics. Namely: the industrial distract > business district ≈ residential distract >tourism district. The concentration of ammonia nitrogen in four functional areas of the possession of absolute advantage, that of inorganic nitrogen in Xi’an City settlement with ammonia.(3) There were great differences in the concentration of heavy metals in atmospheric disposition in different functional areas of Xi’an. The content of Cu, Pb, Zn, Cd in the industrial area is 1.3-1.4 times higher than other functional area, and the concentration of As,Ba, Fe is lower than other functional areas. Except for Cu, Pb, Ba, the content of heavy metals in the business district, residential areas and tourist area.is relatively uniform.The concentrations of heavy metals from high to low is Al>Fe>Ba>Zn>Pb>Cr>As>Cu>Ni>V>Cd,which is consistent with the patterns of heavy metal concentration in perennial cumulative drop of dust. |
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