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WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Journal of Food, Agriculture & Environment Vol.11 (2): 1247-1254. 2013 www.world-food.net Helsinki, Finland e-mail: [email protected] Research on the eco-purification function of urban forests in Beijing Shaoning Li 1, Shaowei Lu 1, Qinghua Pan 1, Yuping Zhang 1, Bo Chen 2 and Xinbing Yang 2 1 Forestry and Pomology Institute, Beijing Academy of Agriculture and Forestry Sciences, 100093, Beijing, China. 2 College of Forest, Agricultural University of Hebei, 071000, Baoding, Hebei, China. *e-mail:[email protected] Received 10 February 2013, accepted 22 April 2013. Abstract 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./cm3), the Beijing Botanical Garden (502.49 pc./cm3), the Summer Palace (414.68 pc./cm3), clearings (170.50 pc./cm3) and downtown (45.08 pc./cm3). 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. Key words: Urban forest, eco-purification function, negative air ion, absorb and sequester pollutants, reduce noise, sequester dust. Introduction Urban air pollution is one of the most important and urgent many domestic scholars, including Ye et al. 11, Wu et al. 12, Liu et environmental crises for human beings. Urban forests play the al. 13, Wang 14, Shao et al. 15, Wu et al. 16, etc., has shown that crucial role of an ecological purifier. Overseas and Chinese reports factors such as the vegetation, the climate, the presence of water mainly focus on the single ecological function of some tree species bodies, the altitude, human activities and pollution have an impact instead of a systematic and integrated study. on the concentration of negative air ions. The forest has the function of environmental purification by Lipophilic organic pollutants, such as polychlorinated biphenyl absorption, filtration, barrier and decomposition and degrades (PCBs), can be eliminated by vegetation 17, 18. He et al. 19, Sun et and purifies the hazardous substances in the atmosphere (such al.20, Luo et al. 21, Han 22, Zhang et al. 23, Lu et al. 24, etc. proved 25 as SO2, chloride, fluoride and NOx) as well as provides negative that greening trees can absorb atmospheric SO2. Shang et al. , air ions and terpenes (such as phytoncid). In addition, forests can Chen et al. 26 and Lu et al. 27 found that forests are strongly block, filter and absorb dust; thus, the forest belt can effectively capable of absorbing and accumulating heavy metals, such as ease the environmental pollution resulting from industry, Cu, Cr, Pb, Zn, etc. transportation, construction and social life 1. Overseas research on the dust absorption capability of forests Aschkinass confirmed the biological significance of negative has mainly focused on the absorption of radioactive particles and air ions in 1902. Overseas studies on negative air ions, such as traces of metal particles 28. Domestic researchers such as Xiong Vartiainen et al. 6, Tammet et al. 7, Venzac et al. 8, Daniell et al. 9 and Qing 29 have noted that the dust absorption capability of and Reiter 10, mainly focus on the mechanism of production and coniferous forests is 33.2 t/hm2 and that of broad-leaved forest is its application in biomedicine 1-6 but ignore the existence of 10.11 t/hm2 in Xinjiang. Yang et al. 30, Sun and Zhu 31, Tao et al. 32, negative ions in forest environments. In recent years, research by Liu and Sun 33, Cheng et al. 34 and Hu et al. 35 also performed Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 1247 relevant research on the dust absorption capability of the main average temperature is 13°C. The coldest days occur in January greening tree species in cities and regions, such as Zhangjiajie, with an average temperature of -3.7°C, and the hottest days occur Harbin, Lanzhou, Jilin, Yueyang and the Pearl River Delta. in July with an average temperature of 25.2°C. The annual average Li and Tao 36 found that the traffic noise on the two sides of a rainfall is 507.7 mm, and rainfall is mainly concentrated in July and road basically generates a normal distribution in time when the August. The frost-free period lasts for 189 days. traffic volume is large. Liu and Chen 37 indicated that noise can be All necessary permits were obtained for the described field decreased by 8~10 dB on roads with greening trees compared to studies. The field was located in Xiangshan Park, Summer Palace, roads without greening trees and that plains of forests in parks Beijing Botanical Garden, Repository of Institute of Forestry and can decrease noise by 26~43 dB. Zhu 38 discovered that the noise Pomology, Shijingshan Pine Park, Outside of Zizhu Yuan, Shuiguan decreases by 12.5 dB after the car noise passes through 12 m tall Great Wall. Our study was obtained their permits. We are sure that poplar leaves and reaches windows on the third floor. no specific permissions were required for these locations/activities. The reports mentioned are mainly studies on a single region or We confirm that the location is not privately-owned or protected in a single factor, although the comparison and measurement of any way. We confirm that the field studies did not involve multiple places and multiple factors possess great value. endangered or protected species. In our study there are a lot of Representative forests in downtown Beijing and the suburbs as typical tree species, they are not endangered and protected species, well as the typical green areas of parks are studied in this research, they are widely planted in Beijing, Hebei, and Neimenggu of China. and the methods of natural monitoring and indoor analysis are used to measure the eco-purification function of forests in Beijing, Measuring contents and methods: such as increasing negative air ions, absorbing pollutants, (1) Negative air ion measurements: The concentrations of decreasing noise and absorbing dust. This study provides basic negative air ions in typical sites with garden flora of Beijing such reference data for selecting forest species with eco-purification as Xiangshan Park, the Summer Palace, the Beijing Botanical capability and furthering the development of city forests. Garden and the downtown area were tested by using the ITC- 201A intelligent portable negative air ion detector. The results Materials and Methods were compared with the results found in clearings without plants. General situation of experimental areas: The observation points The testing was conducted on sunny days in which the airflow and study areas for negative air ions are in the typical green areas was relatively stable and the wind direction and the wind speed of Xiangshan Park, the Summer Palace and the botanical garden had less variation. The measurements were conducted on the 5th, in Beijing; the clearings near the west of the fifth ring road and the 15th and 25th of each month, and the time for the measurements roads near Zhongguancun were selected as contrast observation was set from 9:00 to 12:00 to ensure comparability between each areas along with the downtown observation point. The places measurement point. In July, August and September, the 7:00 to studied in terms of absorbing pollutants were in the Repository of 19:00 period was chosen to measure the daily variation of the Institute of Forestry and Pomology, Shijingshan Pine Park and whole day, and the observations were made once every two hours. the Shuiguan Great Wall. The places studied in terms of noise Three vertical observation gradients (10 cm, 50 cm, and 100 cm decrease are near the main transportation lines, such as the Zizhu from the ground) at the observation points were set for Bridge in the third ring road, the Sihai Bridge in the 4th ring road synchronous measurements.

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