Study On The Polluting Characteristics Of Atmospheric Particulates In Beijing Urban Area

The pollution of atmospheric particulates was currently the main problem in urban air pollution, and people had taken more attention on them due to their complex composition, diverse nature and more harmfulness. Urban air pollution control had become the important fild of study. This paper analyzed some polluting characteristics of atmospheric TSP and PM₁₀ in Beijing urban area, mainly including the concentration distribution, particle size distribution, characteristics of morphology and composition, speciation of atmospheric heavy metals and distribution characteristics of time. The results show that atmospheric particulates had the distribution characteristics of time. The concentration of PM_1.0, PM_2.5 and PM₁₀ changed periodically in twenty hours, and the peak and trough of concentration appeared respectively from 20:00 to 21:00 and from 5:00 to 6:00. The atmospheric particulates of particle size between 0.52 and 1.04μm were the main component part in all particulates of particle size less than 20μm. The concentration of TSP and PM₁₀ in May was higher than June and July, and the proportion of PM₁₀ in TSP was lower in June than May. The SEM-EDX was used to analyze particulates, and the results showed that atmospheric particulates were composed by mineral, soot aggregates, fly ash, biological and other particulates. The mineral particulates mainly came from wind- dust, road- dust, construction dust, industrial dust and secondary products of atmospheric chemical reactions. The soot aggregates particulates mainly came from motor vehicle exhaust and coal-fired. The fly ash particulates mainly came from coal-fired. The biological particulates mainly came from plants. The ICP-MS was used to analyze Cr, Ni, Cu, Zn, Cd, Pb in atmospheric TSP and PM₁₀. The results showed that all kinds of heavy metals contents were higher in winter than others season, and the summer was a little higher than the autumn. The enrichment factor method was used to further analysis, and the results showed that the heavy metal Cu, Zn, Cd, Pb were enriched, which mainly came form anthropogenic source. And the Cr, Ni were not enriched, which mainly came form nature source. The more in-depth study found that the heavy metals from different sources had different speciation distribution. An improved BCR sequential extraction method was used to divide heavy metal into acid extractable form, oxide form, organic form and residual form. The Cr, Ni existed mainly in organic form, and the Cu, Zn, Cd existed mainly in acid extractable form, and the Pb existed mainly in acid extractable form and oxide form in atmospheric TSP and PM₁₀. There was a big difference in species distribution of heavy metal in soil comparing to particulate, and the Cu existed mainly in residual form, and the Pb existed mainly in oxide form. There were little differents on Zn,Cd, which existed mainly in acid extractable form in particulates and soil.The bioavailability of heavy metal was evaluated to found that Cr, Ni, Cu, Zn, Cd, Pb had different hazards to environment. The harmfulness of Zn, Cd was larger than Pb, Cu, and the Ni, Cr had relatively the lower hazard to environment.