Distribution Characteristics Of Atmospheric Particles From Highways And The Retaining Effect Of Greenbelts

Atmospheric particulates, specially fine particulate, can enter the human's lungs which can cause injury to the health and cause urban atmospheric visibility to go down. So the study included the densities and particle size of atmospheric particulates, temporal and spatial variation and the influence became the hot spots of the study of domestic urban atmospheric environment. Road plants were used to eliminate the pollution of atmospheric particulates, and this way was appreciated more and more. The effect of greenbelts and forest belts to reduce the dust-falling and airborne dust was remarkable. This study mainly tested the densities of atmospheric particulates on the two sides of greenbelts which located on the traffic artery of Zhengzhou city, and analyzed distribution feature of atmospheric particulates and purifying effect of greenbelts, and provide support to pollution abatement of road atmospheric particulates.The densities of atmospheric particles included four kinds of grain diameter(TSP,PM₁₀,PM_2.5å’ŒPM₁) were tested on three main roads in Zhengzhou City, and the densities of atmospheric particles on day, in vertical space, in different weather and seasons and in different sampling areas were analyzed, and the results were that: (1) the variation of particles concentration of four kinds of particle sizes from 8:00 to 18:00 show on"L". Particles concentration is high in the morning, low in the afternoon. The densities of atmospheric particles decreased with the increase of vertical height from 20cm to 400cm. The TSP concentrations showed obvious linearly correlation with PM₁₀ concentration, as for PM_2.5 and PM₁ indicated same tendency. (2) In the four kinds of different weather, the densities of atmospheric particles were highest in the first day after rain; the next was sunny day after wind. The densities of atmospheric particles were highest in winter, and the densities in winter and spring were higher than in summer and autumn. (3) The densities of TSP and PM₁₀ in the sampling points of 20m-width greenbelt and 45m-width greenbelt where was six miles distant from the road reduced obviously. And in the greenbelt, the sampling point was far from the road, in where the TSP density was lower. PM₁₀ density in every sampling point in the greenbelt changed indistinctly, the down trending was not obvious. The densities of PM_2.5 and PM₁ in every sampling points of 20m-width greenbelt and 45m-width greenbelt changed indistinctly, the down trending was not obvious.The purifying abilities of the greenbelts along roads whose widths were equal of different to TSP, PM₁₀, PM_2.5 and PM₁ and dust-falling were tested. The results showed that: (1) The purifying abilities of the three kinds of greenbelts whose widths were equal and layouts were different to TSP,PM₁₀,PM_2.5,PM₁ and dust-falling had no marked qualitative difference. (2) The purifying abilities of the five kinds of greenbelts whose widths were different to PM_2.5, PM₁ and dust-falling had no marked qualitative difference, but the purifying abilities to TSP and PM₁₀ had marked qualitative difference. And that showed the purifying abilities of the 5m-width greenbelt to TSP and PM₁₀ were worst, and the purifying abilities of the 15m-width greenbelt, 25 m-width greenbelt, 35 m-width greenbelt and 45 m-width greenbelt to TSP and PM₁₀ had no marked qualitative difference.The dust-holding capacities of the plants in greenbelts along roads were tested, the results showed that: the dust-holding capacities of different plants were different. And the dust-holding capacities of Jasminum nudiflorum, Forsythia Viridissima, Eriobotrya japonica and Kerria japonica were better, and Fraxinus chinensis and Koelreuteria paniculata were lower. The dust-holding capacities of individual plant of Fraxinus chinensis, Prunus cerasiferacv, Salix babvlonica and Eriobotrya japonica were better, and Kerria japonica and Forsythia Viridissima were worse. The dust-holding capacity of individual plant showed that arbors were higher than shrub. The total dust-holding amount was different for the different layout of greenbelts.The micro-configurations of leaf epidermis are observed through scanning electron microscope(SEM),The results showed that the particle-retaining capacity was related to the micro-configurations of leaf epidermis. The particle-retaining capacities of the micro-configurations of leaf epidermis were decreased in the order of villus>groove>cell>strip protuberance, and the particle-retaining capacity was higher when the micro-configurations were denser and the fall between them was larger. The angle of the leaves affected the particle-retaining capacity.