Study On The Air Cleaning Effects Of Urban Green Space System

Urban green space system is an organic whole consisting of various green lands at varieties of scales, which could not only beautify the environment but also function ecologically to absorb air pollutants and fine particles, as well as to abate noises and accommodate local climate. As the process of urbanization gets accelerating and urban environmental problems turn increasingly severe, the ecological effects of urban green space system has widely gained more and more attention, and thus to exploit this function effectively and efficiently would contribute meaningfully to the whole society. At present, given the sound scale and level of urban green space system in Pudong New Area, the experimental conditions required to conduct the researches on this issue are well prepared. Accordingly, regarding the urban green space system of Pudong New Area as research objectives, this paper analyzes the beneficial impact of the urban green space system on local air quantitatively on the basis of studies on several representative green lands with passive samplers. The aim of this paper is to clarify the positive effects that urban green space system exerts on the environment and to provide basic data for evaluating and improving the green lands and thus exploit its ecological benefit to the greatest degree.Considering that there is no complete scientific theory about the approaches to study the ecological benefits of green lands available either home or abroad, this paper constitutes the approach for passive sampling of SO2, NO2 and O3 in the air. And the results of continuously automatic air measurements also prove that, with its justified precision and exactitude, this approach is qualified for indicative measurements.To analyze the distribution characteristics of green biomass of Pudong New Area, this paper constitutes an approach for green biomass estimation which could apply on a city scale. Also, the number and normal green biomass are calculated, and then the green biomass of the whole area is estimated. Base on the foregoing results, the distribution characteristics of the green biomass in this area are discussed and comparisons of the green biomass per capita and the green biomass concentration among the districts are conducted. Through the introduction of the coordinate system into this area, the coordinates of the geometrical centers of parks and districts are fixed and then the coordinates of the centers of green biomass of population in this area are estimated with a bary center approach. Results indicate that the green biomass center overlaps with the geographic center and is to the northeast of the population center.In Pudong New Area, green lands which are sufficiently representative are selected as samples, where the passive sampling approach is used to analyze the green lands' benefits in removing SO₂, NO₂ and O₃ in the air on the basis of a comparison with the results from bare lands without vegetation. And the results show that, all green lands function effectively in removing primary pollutants such as SO₂, NO₂ and O₃, and that in most park green lands and traffic green lands secondary pollutants such as O₃, are also apparently removed, while in some parks the concentration is similar to or even higher than the bare lands, which is probably due to the photochemical reaction produced by hyperactive organic compounds in intense sunlight.To analyze the impact that the green lands' characteristics exerted on the it benefits to the air, this paper selects 6 green belts by Longdong Roads which all measure 15m wide and 20m long, and uses greenbelt porosity, crown closure and green biomass density as the indicators of green lands' characteristics. Results show that higher greenbelt porosity, lower crown closure and higher green biomass density all help to decontaminate the air. And the optimal references of these indicators are: greenbelt porosity 20%, crown closure 0.85, tri-dimensional green biomass density 22.5m³/m², and planar green biomass density 15m²/m².Traffic greenbelts is an important component of urban green space system. To analysis the impact that it's width conducted on the air cleaning effects, this paper, measures the distributing law of air pollutants in the greenbelts. On the basis of wind profile model, constitutes the shifted power-law model-SP model-to describe the distributing behavior of air pollutants in the traffic greenbelts. And the efficiency of this model is justified by existing experimental data.Through analysis for biological and chemical indicators, sulfur contents and nitrogen contents of prevailing vegetations in this area, this paper reveals primarily that the marked correlationship among pH of leaves' cell sap, buffering capacity and sulfur and nitrogen contents, which are also the determinants that affect the plants in absorbing sulfur compounds and nitrogen compounds in the air. And higher pH in leaves and stronger acidic buffering capacity both help to absorb acidic gases in the air such as SO₂ and NOX.