Observations And Assessments Of Mitigation Effects Of The Urban Forests On Atmospheric Pollutants

Two paired experimental sites were established in Changsha and Zhuzhou cities to explore the mitigation effects of urban forests on atmospheric pollutants. At each experimental site, there were paired plots including urban forest plots and bare land plots. In this study, standard methods for monitoring of air and waste gases set by National environment protection bureau of China was employed for monitoring and analyzing. The dynamics of the main air pollutants, that is, SO₂, NO_X and TSP, in the two cities had been monitoring for one year (2003.1-2004.1). Comparisons of mitigation capacities of the air pollutants within different tree species were made. And based on these data and calculations, the main results and conclusions were drawn as the following:(1) The daily variations in the concentrations of the air pollutants were significant both in control aeras and in treatment areas. The concentrations in the morning were higher than that at noon, and then it increased till to the level in the morning in the afternoon, which exhibited a "U" shape.(2) The concentrations of pollutants varied significantly with seasons in every experimental sites. The concentrations of pollutants in the spring and the winter were higher than that of pollutants in the autumn at the annual scale.(3) Air pollutant has obvious difference (p<0.05) related to the function of district; The pollutant density in the area which has city forest structure is lower than the control which has no city forest structure.(4) There were obvious differences in the air quality among the four sampling plots. And the two plots with urban forest were classed as I level in the two cities, while the other two were classed as II level. Generally, the air quality in the two cities was classified as "Good", according to the monitoring results from the four plots.(5) For more, dust removal measurement was taken for 17 trees species in Changsha and Zhuzhou city in Hunan province. The results showed that there were obviously different effects of dust removal among different trees species. Pinus . Thunbergii. Parlata was ideal conifers for dust removal in coniferous trees. It's dust removal abilitieswere2.0131g/ (m2-week) after four weeks, respectively P. acerifolia Willdand O.fragrans Lour, were ideal tree species in broad-leaf trees, their dust removal abilities were respectively 5.0645 g/ (m2week) and3.3952 g/ (m2-week) after two weeks. E.japonicus Thunb.was the best species in shurbwhich dust removal abilities was 7.172 g/ (m2-week) . (6) According to the Pollutant Load Coefficient (fi) of all pollutants, the main varieties of pollutants were SO2 and TSP (fS02 =64.36%>fTsp=26.51%>fNOx=12.64%).