Li, S; Lu, S; Pan, Q; Zhang, Y; Chen, Bo; Yang, X
The eco-purification functions of urban forests, such as increasing negative air ions, absorbing and sequestering pollutants, reducing noise and sequestering dust, were measured by methods of nature monitoring and laboratory analysis in Beijing. The result showed the following: The presence of garden flora can significantly increase the concentration of negative air ions, and the annual average concentration of air ions can be sorted in descending order as Xiangshan Park (630.25 pc./cm(3)), the Beijing Botanical Garden (502.49 pc./cm(3)), the Summer Palace (414.68 pc./cm(3)), clearings (170.50 pc./cm(3)) and downtown (45.08 pc./cm(3)). The temporal and spatial variation in the concentration of negative air ions was quite obvious in different habitats in the order of autumn, summer, spring and winter from the most to the least variation. However, it showed a single peak curve monthly. The maximum value appeared in September. The larger values appeared at 9: 00 and 15: 00 in the daytime, and the emergence of the minimum varied but was generally approximately 19: 00. With the increase of the vertical observation gradient, a single-peak variation trend emerged. Among the environmental impact factors, the relative humidity and the temperature were dominant, and the wind speed and the canopy density were relatively minor. In this paper, we assessed the air quality of each observation area according to the concentration distribution of negative air ions. 1) The ability to absorb pollutants varies greatly by tree species. The content of pollution elements in different tree leaves can be generally sorted in descending order as S, Cl, Zn, Cu, Cr, Pb, As, Hg and Cd.2) The ability of different tree species to absorb dust (based on the dry weight of dust in their leaves) can be sorted in descending order as purple leaf barberry, Chinese scholartree, euonymus fortunei, buxus microphylla, euonymus, Chinese red pine, oriental arborvitae, poplar, pear, peach, apricot, apple and cherry. 3) For the forest belt of the 3rd, 4th and 5th ring roads, the effect of noise reduction is best at the points that are 10 m, 150 m and 50 m from the road, with noise reduction rates of 8.39%, 5.81% and 6.91%, respectively. There is a significant cubic function regression relationship between the noise reduction capacity of the forest belt of the ring roads and the distance.