| As the smaller size particles, PM25 is difficult on its own gravitational sedimentation, which represents a serious threat to human health as well as environment quality, while vegetation has positive effect on regulating and retaining atmospheric particulates such as PM2.5. Based on Beijing air monitoring site data, this paper analyzed spatial distribution and temporal variation of Beijing PM2.5 concentration, and compared the distribution of PM2.5 in different periods with different vegetation coverage. At individual tree and foliage scale, the reduction and retention effect of common tree species in Beijing and Chongqing municipality were measured. This study attempted to quantify the PM2.5 retention effect of plant, and to provide a reference for the city from the perspective of plant measures to reduce the particle pollution.(1) Choosing Beijing as the typical study area, PM2.5 spatial distribution during vegetation growth and non-growth period of Beijing area was obtained by interpolation method. The average concentrations of PM2.5 during vegetation non-growth period were significantly higher than vegetation growth period, and PM2.5 concentration was much higher in districts with low vegetation coverage in the same period. Spatial variability analysis of the particle distribution showed that the presence and growth of vegetation will disturb the distribution of PM2.5 to some extent, consequently reduce spatial correlation of particulate matters. Based on model estimation, the annual average reduction of PM2.5 varied among the city from 50 to 180mg/m2 of canopy cover in different districts of Beijing. Differences between districts were significant and districts with higher reduction usually linked with a relatively high particle pollution levels.(2) At individual tree scale,20 common species of street trees and greening trees in Beijing and Chongqing were chosen, retention of PM2.5 per unit leaf area in each kind of species were obtained through simulated experiment with an air chamber and retention of PM25 in different species individual tree were estimated combined with empirical equation. In terms of PM25 retention per unit leaf area, differences between species were significant, and it was generally varied from 1.5 to 2.5mg/m2. Cunninghamia lanceolata and Grevillea robusta showed higher retention of the tested tree species, while Ginkgo biloba, Cinnamomum japonicum and Magnolia soulangeana were relatively low. In terms of PM2.5 retention of individual tree, it was obviously that Cunninghamia lanceolata was higher than the other kind of species and the average PM2.5 retention was up to (485.71±45.06) mg. Pinus armandii, Grevillea robutstaalso had a relatively better retention capability compared with Ginkgo biloba, Cinnamomum japonicum, Platanus occidentalis.(3)At foliage scale, combining with SEM analysis, four indicators which were the groove ratio, total number of leaf hair per unit area, stomata density and stomata size (the long axis of the stoma radius) were chosen and classified to quantify the leaf surface microstructure of different species and focused on studies that the influence of different leaf surface microstructures on retention of PM25 per unit leaf area-PMk2.5 retention per unit leaf area of different species had significant positive correlations with groove ratio and total number of leaf hair separately, but relationships with stomata density and stomata size were not significant. Linear fitting analysis showed that fitting relationship between the retention of broadleaved species and the microstructureswas obviously better than that of coniferous species, manifesting that leaf surface microstructure had greater impact on PM2.5 retention in attachment. Result of relationships between microstructural level characteristics and PM25 retention indicated that the level which groove ratio greater than 20%, total leaf hair greater than 50per unit area, stomata size larger than 20μm and stomata density greater than 100mm-2 could retain highest PM2.5. |
PDF Full Text Request