Study On The Pollution Characteristics And Environmental Hazard Evaluation Of Atmospheric Heavy-metals In Chengdu City

Air particulate matter pollution is the primary factor which affects China's urban air quality, morever study on atmospheric heavy-metals is a hot topic in the fields of contemporary environmental sciences and atmospheric chemistry. The environmental harmfulness of atmospheric heavy-metals (including environmental behaver, the capacity of transport and transfer and bioavailability, etc.) largely depends on the state of heavy metals, which is affected by the particle size, time and space. Thus, the feature of atmospheric heavy-metal pollution is very complicated. Air quality standard in china regulates that the total amount Pb in TSP is the only rating factor considered for heavy metal pollution of the atmosphere. It is obvious inadequate because the type, form, size distribution and other factors of heavy-metals are not fully considered. In this study two monitoring sites (E locations in the eastern district of Chengdu City and W locations in the western) were estabilished. Atmospheric particles (PM₁₀ and TSP) in the two locations are the main concerned, and the. pollution Characteristics of atmospheric particles and the distribution patterns of atmospheric heavy metal are focused on. In order to improve the atmosphere quality standard, and provide a scientific assessment methed for monitoring urban atmospheric environment. The Analytical Hierarchy Process(AHP) is first time applied in the assessment of air heavy metal pollution, combined with previous research results on heavy metals.The research is focused on the distribution of particles in different space anddifferent time,ie. day and night, based on the fact that particle size is an important characteristic and the heavy metals mainly in small size particles. The paper has analyzed ten kinds of heavy metals, Pb,Zn,Cu,Cd,Ni,Gr,V,Co,Mn,Ca, in the two monitoring sites in Chengdu, by using the methods of microwave digestion, flame atomic spectrophotometer and inductively coupled plasma mass spectrometry (ICP-MS). The results show that, the heavy metals of the atmospheric particles in Chengdu, especially V,Cd,Co,Pb, are mainly distributed in relatively small size of particles (PM₁₀). The differences between those ten heavy metals are very obvious. The content of Ca elements is the largest; followed by elements Zn, Pb, Mn and Cu; elements V, Cr, Ni, Cd are relatively low; the minimum is elements Co. the spatial distribution of heavy metals concentration of the atmosphere is higher in the east of chengdu than that in the west, and the remarkable differences are in the elements of Cd,Zn,Cu,Pb, and minimal in the elements of Ni and Cr.A three-stage sequential leaching procedure was applied to analyze the fonn of heavy metals in the atmospheric. By this methed it can separate atmospheric particles into the forms of exchangeable, carbonate and oxidation, organic and residue state. Data analysis showed that, the larger percentages content of exchangeable heavy metals are Pb, Cd, Mn and Ni, and the smaller of those are Zn,Cu and Cr. The forms of heavy metals in the atmospheric also change with the spatial distribution. The total percentage content of exchangeable Pb,Zn,Cr in the point west is higher than that in the point east, and much higher in that of Pb,Zn,Cr, but there is little change of V with the spatial variation. Most of heavy metals show that the percentage content of exchangeable elements will be much larger and the activity of the environment will be much stronger, when their sizes are smaller . While the chemical state distribution of V and Co are relatively stable , which show that the sizes of particle have little impact on the environmental activity.The paper chose six high environmental activity heavy metals element as the object of study, based on the total content and distribution of heavy metals of particles in Chengdu, and the combination of heavy metals bioaccumulation model and other heavy metals research results. This paper first time use an analytical hierarchy process to access the weight of environmental harmfulness of heavy metals. It is shown that Pb is of the greatest weight, and Cd has the weight after Pb, but Cu,Cr,Ni,Zn are also have large weigh in environmental harm. This indicates that the assessment and prevention of atmospheric pollution should consider the shape, size distribution.