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

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, . 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 (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. After the testing instruments were and the Yufeng Bridge in the in Beijing. The places sufficiently stable for measurement, 8-12 peak values were studied in terms of dust absorption are near the roads where the measured, and for the areas where the data changed drastically at traffic volume is large and dust is plentiful, such as Minzhuang every gradient, the average value was calculated as the value of Road and Xiangshan Road near the west 5th ring road in Beijing. the negative air ion concentrations at the observation point. The observation spots listed above are in the northwest of Beijing (N39°56’ and E116°20’) in a temperature zone influenced by (2) Pollutant absorption ability measurement: More than ten Mongolian high pressures and subject to the continental tree species with 10 to 20 growing years at medium vigor were monsoon climate. They have four distinct seasons, and the annual chosen for the study on the pollutant absorption ability of trees

Table 1. General description of each experimental spot. S/N Sampling Spots General Situation and Habitat Description of Sampling Spots It is located in the forest park of West Mountain in Beijing, subject to mountain and forest areas with 1 Xiangshan Park little pollution, plenty of Chinese red pines, platycladus and maple trees, canopy density of 98% It is located in an artificial garden of the northwest suburb of Beijing, beautiful environment, little 2 Summer Palace pollution, with over 1600 ancient and famous tress and 3/4 water surface area It is located near Xiangquanhuan Island outside of the fifth ring road in the northwest of Beijing. 3 Beijing Botanical Garden Typical garden plant species are preserved in the garden with little pollution, canopy density of 75% Repository of Institute It is located in the fifth ring road in northwest Beijing; numerous of germplasm resources of fruit trees 4 of Forestry and Pomology are preserved with little pollution, and it is far from the road It is located in the industrial area near Shijingshan Bajiao with a large traffic volume and serious 5 Shijingshan Pine Park industrial pollution, plenty of Chinese red pines and platycladus, canopy density of 90% It is located near the road in the urban area of the western third ring road with a large traffic volume 6 Outside of Zizhu Yuan and severe pollution due to vehicle exhaust, and the trees near the road are gingko and sophora japonica It is located in the mountain and forest of Shifo Temple in Yan Qing, with little manmade and 7 Shuiguan Great Wall industrial pollution, plenty of Chinese red pines, platycladus, apricot tree sand peach trees, canopy density of 95%

1248 Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 according to the statistical data and the wild survey of common country have also proposed some evaluation indexes, such as tree species of Beijing. Pinus tabulaeformis, Platycladus the monopole coefficient (q), the ampere air quality evaluation orientalis, and Sabina chinensis were chosen in Xiangshan Park coefficient (CI), air ions in the forest evaluation coefficient (FCI), and at the Beijing Botanical Garden. Sophora japonica Linn and the ratio between heavy ions and light ions, the relative intensity Ginkgo biloba were chosen downtown (outside the Black Bamboo of air ions and the negative air ion coefficient, among others 40-42. Garden). Pinus tabulaeformis, Platycladus orientalis, Berberis Among these choices, the monopole coefficient and the ampere thumbergii ‘atropurpurea’ and Buxus microphylla were chosen air quality evaluation coefficient were the most widely applied. at the Pinery Forest Garden in the Shijingshan District. Pinus The variables q and CI were used in this study. The formula was tabulaeformis, Platycladus orientalis, Sabina chinensis, Pinus q=n+/n-, CI= (n-/1000)q-1, in which n+ and n- represent the armandii Franch, Pinus bungeana, Armeniaca sibirica and concentration of the positive and negative air ions, q represents Prunus davidiana were chosen at Badaling Great Wall. Fruit tree the monopole coefficient and CI represents the air quality species with a wide planting area and excellent growing tendency evaluation index. in Beijing, such as Malus domestica Borkh ‘Red Jiangjun’, Pyrus The air quality evaluation coefficient (CI) refers to the degree spp. ‘XG Fengshui’, Amygdalus persica Linn ‘Wanmi’, Armeniaca that the ion concentration in the air approaches the level of the air vulgaris ‘Chuanzhihong’, Sabina chinensis, Platycladus ion in the nature. It can be divided into five grades (Table 2). orientalis, etc., were chosen at the Resource Garden of Beijing Table 2. Air quality grading. Institute of Forestry and Fruit. Grade Air quality Air anion assessment index (CI) The leaves of different tree species at the experimental areas A Clearest ˚1 were collected in spring, summer, autumn and winter. Three backups B Average 1̚0.7 were prepared for each tree species. That is, soil samples in the C Moderate 0.69̚0.50 soil sections of 0 – 5 cm, 5 – 20 cm, and 20 – 40 cm near the tree D Allowable 0.49̚0.30 were taken with an earth-boring auger. Because the dynamic E Critical 0.29 variation of the heavy metal content in the soils was not obvious, the soil samples were only taken once in September, and the value (2) Anti-matter ability per net mass=anti-matter ability of the found was assumed to be the heavy metal content in the soil year- leaf/net mass of the leaf: Anti-matter ability per m2 = (anti-matter round. The collected leaves and soil samples were taken to the ability of the leaf*mass of the punching part of 20 leaves)/ (area of laboratory for relevant treatment to measure their pollutant the punching part*total mass of 20 leaves) contents. Data processing: The drawing and the data analysis was (3) Noise reduction measurements: According to the actual performed with Excel 2003, and the analysis of variance and situation, the observation points were set at the noise source and significance was completed with SPSS 11.5. 5, 10, 20, 30, 40 and 50 m above the noise source. The observations were conducted at 1.2 meters in daytime when it was sunny and Results with relatively low wind speed. The exact time in one day was Studies on the distribution characteristics of negative air ions from 9:00 to 12:00. The same observation method was applied to in the green areas of typical parks: the comparison places using a CEL-320 personal noise dosimeter, (1) Temporal and spatial variation characteristics of negative 5 min of measuring time, 3 repeated measurements for each air ion concentrations in the green areas of different parks: The observation point, 1 h for each interval and 100 types of data temporal and spatial distribution of negative air ions varied greatly chosen for each observation point for analysis and comparison. without uniform or consistent laws. However, the distribution was affected by the place, grass and meteorological factors, etc. (4) Anti-matter ability measurements: Platycladus orientalis, According to previous studies by Liu et al. 13, Shao et al. 15 and Pinus tabulaeformis, Buxus microphylla, Berberis thunbergii Wu et al. 16, the average concentrations of negative air ions at ‘atropurpurea’, Sophora japonica Linn., Euonymus alatus, different observation points year-round can be sorted in Populus canadensis Moench, Euonymus fortunei (Turcz.) Hand.- descending order in this study as Xiangshan Park (630.25 ions/ Mazz., P. persica, P. armeniaca, Pyrus pyrifolia, Malus pumila cm3), the Beijing Botanical Garden (502.49 pc./cm3), the Summer Mill, Cerasum and Cerasus, etc. were chosen to measure their Palace (414.68 ions/cm3), clearings (170.50 ions/cm3) and anti-matter ability. downtown (45.08 ions/cm3). In particular, the concentration at The samples were collected from the experimental areas one Xiangshan Park (the highest) was 14 times greater than that of week after raining. Three samples that comprehensively integrated downtown (the lowest) due to the presence of more plants in different positions of the tree, such as around, above, in the middle Xiangshan Park and the Beijing Botanical Garden than at the of, and under the tree crown, were collected for each type of tree Summer Palace. Although there was less grass in the clearings species as representative samples and were taken to the laboratory and there were many people, cars and pollution downtown, the to measure their anti-matter ability. The leaf area was measured amount of negative air ions was less, and the their persistence through the punching and weighing method. was very short, which resulted in the lower concentration of negative air ions than the concentrations at the other three Calculating and assessing methods: botanical areas. (1) Air quality evaluation method: Huang et al. 39 found that the The negative air ion concentrations at different observation air would be cleaner and people would feel more comfortable if the areas presented the same trend with height (from the ground). negative air ion concentration was higher. Scholars outside the The negative air ion concentration decreased when the height

Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 1249 increased. As shown in Fig. 1, the negative air ion concentration

had a large variation at different heights in the Botanical Garden -3 cm but was relatively steady downtown. ·

-3 cm · Negative air ion

Month

Negative air ion Figure 3. Daily mean variation in the concentration of negative air ions.

relatively high value of the negative air ion concentrations in the Grads/cm Beijing Botanical Garden, the Summer Palace, clearings and Figure 1. Spatial gradient curve of the negative air ion concentrations at downtown appeared at 9:00 and 15:00, and the largest value different observation areas. appeared at 15:00. While the time when the lowest value of negative air ion concentration of different areas varied greatly, it appeared According to Fig. 2, with the increase in altitude, the negative at 19:00 in the Beijing Botanical Garden and the Summer Palace air ion concentration in Xiangshan Park presented a single-peak and at 7:00 in the clearings and downtown. The negative air ion curve with a maximum value at 400 m because the negative air ions concentration variation of Xiangshan Park was very different than cannot be maintained due to the lower grass coverage on the top those of the other observation areas. Its largest value appeared at of the mountain and the high wind speed. However, in the maple 7:00 and then began to decrease until another peak value occurred tree region (the middle part (400 m) of the mountain), there was at 17:00, with the lowest value at 15:00. sufficient sunshine, and the air was fresher than that at the Wu et al. 12, Wang 14, etc. noted that the spatial and temporal mountain bottom, which was conducive to photosynthesis to distributions of negative air ions did not have obvious and produce more negative air ions that persisted for a longer period consistent rules. However, this study discovered that there are of time. obvious rules at the experimental points selected, and the differences between them were very significant. The annual variation curves for the negative air ion concentrations of different

-3 observation areas were almost the same, that is, they had a single cm · peak (Fig. 4). The largest values of the negative air ion concentrations in Xiangshan Park, the Beijing Botanical Garden, the Summer Palace, clearings and downtown occurred in September, and the lowest values occurred in February, with annual Negative air ion variations of 1714 pcs./cm3, 744 pcs./cm3, 524 pcs./cm3, 290 pcs./ cm3 and 65 pcs./cm3, respectively, which indicated that the negative

Altitude/m air ion concentration was greatly affected by many factors Figure 2. Vertical change in the negative air ion concentration at Xiangshan including the green coverage, the temperature, the humidity, etc. Park.

The regression relationship between the negative air ions and the altitude is: -3 cm ·

Y = -0.01X2 + 8.58X -847.31(R2 = 0.8197)

In this Equation, Y represents the negative air ion concentration (unit: pcs/ cm3), and X is the altitude (unit: m). The regression of Negative air ion the Equation is significant and shows that the negative air ion concentration and the altitude fit the equation above well; thus, Time this equation can be used to calculate the negative air ion Figure 4. Annual mean variation in the concentration of negative air ions. concentration of Xiangshan Park at different altitudes. Fig. 3 shows that the negative air ion concentration of Xiangshan (2) Relationship between the negative air ion concentration Park varied greatly in the daytime, while that of the other four and the environmental factors in different garden flora areas: areas had a smooth variation. The great difference between the The variation of the negative air ion concentrations and concentration in Xiangshan Park and in the other observation environmental factors of different observation areas were almost areas was mainly because the negative air ion concentration varied the same and were positively correlated to each other (Figs 4- 6). greatly in the daytime due to different altitudes. The daily variation The negative air ion concentrations of different observation areas of the negative air ion concentration in forests has been studied always increased with an increase in the temperature and the by Wu et al. 12, Shao et al. 15, etc. This study showed that the humidity. The temperature and the humidity presented a single

1250 Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 The absorption and purification ability of different tree species varied. Berberis thunbergii ‘atropurpurea’ has the strongest

ability to absorb Cu and the weakest ability to absorb Cd. Pinus C ° tabulaeformis has the strongest ability to absorb Hg and the weakest ability to absorb Cl. The absorption ability of Platycladus orientalis for As and Pb was strongest. The absorption ability of Buxus microphylla for Cr and Cl was strongest. The absorption ability of Salix babylonica for Zn and Pb was strongest.

Average temperature/ Average Table 4 shows that cypress has the strongest absorbent power for As, Pb, Cr and Cl; bungeana has the strongest absorbent Month Figure 5. Annual mean curve of the average temperature. power for Zn, Hg and S; oriental arborvitae has the strongest absorbent power for Cd; and davidiana has the strongest absorbent power for Cu. It is obvious that different tree species have different absorbent powers for different pollutants. Both 90.00 80.00 cypress and bungeana have strong absorbent power; oriental 70.00 arborvitae and davidiana also have strong absorbent power for 60.00 some heavy metals. Thus, the proper tree species can be chosen 50.00 40.00 to purify the environment according to the practical situations of 30.00 20.00 different pollution zones. 10.00 Relative humidity/% 00.00 1 2 3 4 5 6 7 8 9 10 11 12 2) Analysis of ability of the main fruit tree species to absorb and Month sequester pollutants: Table 5 shows that apricot - Chuanzhihong Figure 6. Annual mean curve of the relative humidity. has the strongest absorbent power for S, and apricot - Longwangmao has the strongest absorbent power for Cu and Cd. peak shape year-round, with peak values in July to August, and Peach - Wanmi has the strongest absorbent power for Zn and Cl, the peak value of the negative air ion concentration occurred in and apple - Hongjiangjun has the strongest absorbent power for September. The higher negative air ion concentration in summer As and Pb. Pear - XG Fengshui has the strongest absorbent power was because the humidity in autumn was relatively low and the for Hg and Cr. strong photosynthesis of green plants directly promoted the The Hg content in the leaves of the fruit tree species studied, production of negative air ions. However, many conditions in the except that in Amygdalus persica Linn ‘Wanmi’, presented a winter were not as conducive to the production and existence of gradually increasing trend with seasonal change, which was negative air ions, and thus, the concentration was relatively low. significantly higher in the autumn than in the spring (ρ = 0.023<0.05). The variation of the negative air ion concentration was the result The Pb content in leaves of fruit tree species was significantly lower of the interaction between many factors, particularly the in the spring than that in the summer and autumn (ρ<0.01). The Pb temperature and the humidity. content in leaves of Pyrus spp. ‘XG Fengshui’ was significantly lower than that in other fruit tree species (ρ<0.05). There existed a Study on absorbing and sequestering pollutants with different significant difference in the seasonal Pb content in leaves, with the tree species: most remarkable difference occurring in the leaves of Malus domestica 1) Study on the pollutant purification function of different tree Borkh ‘Red Jiangjun’ and Amygdalus persica Linn. ‘Wanmi’. The species at the same place: The seasonal pollutant concentration seasonal change in the pollutant content in the leaves of Armeniaca in leaves of different tree species at Pine Park is shown in Table 3. vulgaris ‘Chuanzhihong’ was relatively steady; however, it was much

Table 3. Pollutant contents of the leaves of different tree species in Pine Forest Park (mg/kg). Pollutants Content Tree species Cu Zn As Hg Pb Cd Cr S Cl Salix babylonica 6.99 50.30 0.14 0.04 2.13 0.87 3.18 8916.07 1113.31 Berberis thumbergii ‘atropurpurea’ 9.32 29.26 0.26 0.06 4.85 0.07 7.47 2563.77 2724.59 Buxus microphylla 6.66 21.66 0.26 0.06 2.91 0.08 9.84 2245.14 4678.39 Platycladus orientalis 4.37 19.19 0.36 0.06 4.97 0.13 4.52 1614.39 1309.35 Pinus tabulaeformis 6.46 22.17 0.33 0.07 4.19 0.10 6.20 2033.30 559.80

Table 4. Pollutant Contents of Leaves of Different Tree Species at the Shuiguan Great Wall (mg/kg). Pollutants Content Tree species Cu Zn As Hg Pb Cd Cr S Cl Pinus tabulaeformis 4.68 20.06 0.07 0.05 1.69 0.09 2.76 1766.08 446.34 Platycladus orientalis 2.90 19.99 0.23 0.04 2.34 0.29 2.08 1351.30 551.79 Sabina chinensis 3.89 27.99 0.53 0.05 3.72 0.23 8.18 1590.11 578.02 Armeniaca sibirica 3.79 18.32 0.22 0.06 3.28 0.06 5.36 1537.05 482.82 Prunus davidiana 5.19 26.21 0.40 0.09 3.20 0.07 2.86 1830.31 510.04 Pinus bungeana 4.96 51.46 0.23 0.10 3.37 0.03 1.53 2163.56 459.51

Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 1251 Table 5. Pollutant contents of leaves of different fruit trees (mg/kg). Pollutants Content Tree species Cu Zn As Hg Pb Cd Cr S Cl Armeniaca vulgaris ‘Chuanzhihong’ 6.05 21.46 0.29 0.07 3.33 0.07 3.59 1971.69 419.15 apricot – Longwangmao 7.48 22.09 0.28 0.06 2.54 0.10 3.78 1804.98 589.40 Armeniaca sibirica 5.44 23.58 0.32 0.06 3.23 0.05 2.74 1593.25 630.02 Prunus davidiana 4.60 21.33 0.31 0.07 2.91 0.07 6.29 1657.74 317.85 Amygdalus persica Linn ‘Wanmi’ 5.24 25.91 0.30 0.07 2.34 0.06 4.15 1917.15 1010.08 Malus domestica Borkh ‘Red Jiangjun’ 5.72 16.57 0.57 0.08 7.46 0.06 3.37 1720.20 957.64 Pyrus spp ‘XG Fengshui’ 5.61 21.54 0.45 0.15 2.46 0.07 6.50 1626.70 723.02 higher in summer than in spring and autumn in the leaves of The pear tree has the best unit area dust sequestration ability and Armeniaca vulgaris ‘Longwangmao’. the peach tree the worst. Thus, it is clear that pear has a stronger Due to the combination of the physiological characteristics of ability to sequester dust among the economic tree species. the tree species and environmental pollution levels studied, the pollutants could be absorbed and purified by major fruit tree Study of the noise reduction function of trees: The average traffic species. The order of absorption ability to pollutants was as flow of the was 7928 vehicles/h during the observation follows: S> Cl > Zn > Cu > Cr > Pb > As > Hg > Cd. The highest and period, among which larger vehicle accounted for 5.78%. The lowest pollutant contents in the leaves of the fruit tree species magnitude of the noise was closely related to the presence of studied differed by approximately 1 to 3 times. larger vehicles, which could result in an instantaneous, significant increase in the noise level. The noise reduction value at the 50-m Study on the function of trees for sequestering dust: Table 6 point of the forest belt from the 3rd ring road was measured to be shows that the purple leaf barberry has the strongest capacity to 17.9 dB, and the noise reduction rate was 20.86%. The noise sequester dust based on the dry-weight of dust on the leaves in a reduction effect was most significant at the 10-m point from the single week, which was 5.9 times that of poplar. The dry-weight of forest belt from the 3rd ring road among different distances of the dust on leaves in a single week is largest for the purple leaf barberry, forest belt, with a net attenuation value of 7.2dB and a noise and the others in descending order are Sophora japonica, reduction of 8.39%. The noise reduction effect was weakest at the Euonymus fortunei, pear, Buxus microphylla, euonymus, peach, 40-m point, with 3.2dB of net attenuation and only 3.73% of the apricot, apple, cherry, pine, oriental arborvitae, and poplar. Among noise reduction rate. The average traffic flow of the 4th ring road these trees, Sophora japonica has the highest dust sequestering was 6764 vehicles/h during the observation period, among which ability per area, which is 11.9 times of that of Buxus microphylla. larger vehicles accounted for 4.17%. The noise reduction level at The ability to sequester dust by unit area can be sorted in the 150-m point of the forest belt from the 4th ring road was 16.4dB, descending order as Sophora japonica, Euonymus fortunei, with a noise reduction rate of 19.85%. The noise reduction ability purple leaf barberry, Euonymus, poplar, pear, apple, cherry, apricot, at the 150-m point from the 4th ring road was strongest, with a net peach, and Buxus microphylla (excluding coniferous species). attenuation value of 4.8dB and a noise reduction rate of 5.81%. In terms of different arbuscles, the purple leaf barberry The belt at the 5-m point had the weakest noise reduction ability, sequesters the highest dry-weight of dust, which is more than with only 2.4dB of net attenuation and a 2.91% noise reduction double that of the euonymus. It is followed by Euonymus fortunei, rate. which sequesters 1.7 times the dust dry-weight of the euonymus. The average traffic flow of the 5th ring road was 5895 vehicles/h Euonymus fortunei and the purple leaf barberry are dominant in during the observation period, among which larger vehicles dust sequestration in terms of the unit area, which shows that accounted for 3.53%. The noise reduction level at the forest belt Euonymus fortunei and the purple leaf barberry have a stronger 100 m from the 5th ring road was 18.6dB, with a noise reduction rate ability to sequester dust. Thus, cultivation can be appropriately of 22.17%. Among the different distances into the forest belt, the added in road greening to enhance the dust sequestration effect. belt at the 50-m point had the strongest noise reduction ability, Among the various economic trees, the pear tree leaves have the with 5.8dB of net attenuation and a 6.91% noise reduction rate. highest dry-weight level of dust, and the cherry tree has the lowest. The belt at the 5-m point had the weakest noise reduction ability,

Table 6. The ability to sequester dust for different tree species in a single week. Dry-weight of Leaf area Dust sequestration Ability to sequester Plants sequestered dust (g/g) (cm2) ability per area (g) unit-area dust (g/m2) Sophora japonica Linn. 0.1767 0.4976 0.0082 164.1796 Populus canadensis Moench 0.0315 4.7514 0.0357 75.2192 Euonymus fortunei (Turcz.) Hand.-Mazz. 0.1566 0.4389 0.0053 121.6602 Euonymus alatus 0.0903 0.8462 0.0086 101.3905 Buxus microphylla 0.1014 0.1161 0.0002 13.7812 Berberis thumbergii ‘atropurpurea’ 0.1852 0.1532 0.0017 107.8822 Malus pumila Mill. 0.0722 3.0166 0.0136 45.2164 Pyrus pyrifolia 0.1028 5.2140 0.0254 48.7418 P. persica 0.0837 2.5652 0.0100 38.8655 P.armeniaca 0.0744 4.3404 0.0188 43.4190 Cerasum and cerasus. 0.0512 3.5857 0.0161 44.9224 Platycladus orientalis 0.0404 — — — Pinus tabulaeformis 0.0464 — — —

1252 Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 10.0 3rd ring road directly influences the generation and existence 4th ring road 9.0 of negative air ions. It is obvious that the main 5th ring road 8.0 meteorological factors influencing the negative air 7.0 ions are temperature and humidity. The wind speed 6.0 will greatly impact the evenness of the distribution 5.0 of anions but not the total level of anions. The 4.0 canopy density also has an impact on the anion 3.0 density, but the impact is slighter. Net attenuation/dB 2.0 Previous studies on the function of plants in 1.0 absorbing and sequestering pollutants have not 0.0 5 10 20 30 40 50 Distance/m often discussed fruit trees. The significance of this study lies in its comprehensive analysis of the Figure 7. Comparison of the noise reduction ability at different distances from each absorption and sequestration of pollutants in the ring road. leaves of different fruit tree species. For example, Table 7. The relationship between the net attenuation value of noise and the Pb level in the leaves of apple trees – the distance of each ring road. Hongjiangjun and peach trees – Wanmi in autumn Points Function formula R Sig. is 27.5 and 16.9 times greater than that in spring, The 3rd ring road Y=-0.0007x3+0.0559x2-1.5080x+84.9977 0.969 0.009 respectively. Such a sharp difference shows that The 4th ring road Y=-0.00002x3+0.0049x2-0.4245x+79.4055 0.875 0.011 the apple – Hongjiangjun and the peach – Wanmi The 5th ring road Y=-0.00007x3+0.0119x2-0.6863x+82.2453 0.949 0.005 trees are sensitive to the change in the Pb level In the formula, Y represents the net attenuation value of the noise (unit: dB) and x represents the distance of forest belt from the noise source (unit: m). and can serve as the plant indicator of Pb pollutants. with only 1.5dB of net attenuation and a 1.79% noise reduction This study has proven that economic tree species have rate. significant dust sequestration effects but that this sequestration Fig. 7 shows that the noise reduction effect of the forest belt ability is associated with a variety of factors. Having a wrinkled, around the 3rd ring road was clearly better than that around the 4th rough, hairy or fatty leaf surface is the key influence factor because ring road and the 5th ring road. The greatest noise reduction was these characteristics beneficially hinder, absorb and adsorb the typically at the 10-m point from the 4th ring road or the 5th ring road, atmospheric particles. Meanwhile, the dust sticking level has a where the noise reduction ability was a factor of 2.67 and 3.79, relationship, to some extent, with the canopy structure, the foliage respectively. The measurement of the noise was greatly influenced density and the leaf inclination; it is also bound by such by the random role of the traffic environment, which had an impact meteorological factors as wind and rain. Additionally, the actual on the measurement results to some extent, which is associated situation of the test sample plot (including civil engineering and not only with the distance of the noise source but also with the construction and transportation) will also have a certain impact vegetation configuration. Fig, 7 indicates that the noise reduction on the experimental results. capability of the forest belt of each ring road exhibited a cubic This study has found that the noise reduction capability of the functional relation with the distance and that there is an obvious forest belt of the ring roads exhibits a cubic functional relation regression relationship. with distance. This study also found that there is an obvious regression relationship, which is very different than the normal Discussion distribution in the study by Li and Tao 36 because the noise As reported by Reiter 10, Shao et al. 15 and Ye et al. 11, the reduction effect is not only associated with the traffic conditions concentration of negative air ions is closely related to but also with the characteristics of the green belt. Therefore, apart meteorological elements due to sharp differences in the regions, from measures such as reducing traffic flow, more forest belts the vegetation and the meteorological phenomena studied. They should be planted along both sides of the roads to reduce noise all agreed that environmental factors such as the air temperature, and improve the urban environment. the relative humidity, wind, rain, fog and the solar radiation 15-18 were important influencing factors, but their conclusions were Acknowledgements different. According to full-year data, the difference in the average This work was financially supported by the Special Fund for temperature at every observation point was not large, and the Forestry Scientific Research in the Public Interest (No.201204108) temperature fluctuation at Xiangshan, which had more trees, was and the CFERN & GENE Award Funds for Ecological Papers. smaller. The experimental results showed that the air temperature and the humidity at each observation point are positively correlated with the concentration of negative air ions. Throughout References 1 the year, the temperature and humidity change in a single-peak Wang, B.,Yang, F.,Guo, H., Li, S., Wang,Y., Ma,X.,Yu, X., Lu,S., Wang,H. and Wei,W. 2008. Assessment Program of Forest Ecosystem Services trend, and the peak value is generally in July and August. The Value. LY/T 1721-2008. China Standards Press, Beijing. peak value of the concentration of negative air ion emerges in 2Phillips, G., Harris, G.J. and Jones, M.W.1964. Effect of air ions on September, mainly because the air is fresher and the humidity is bacterial aerosols. International Journal of Biometeorology 8(1):27- lower in autumn. Moreover, the slightly higher negative air ions in 37. autumn are mainly because the air is fresher and the humidity is 3Krueger, A. P. and Reed, E. J. 1976. Biological impact of small air ions. lower in autumn, and the strong photosynthesis of green plants Science 193:1209-1213.

Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013 1253 4Krueger, A. P. 1985. The biological effects of air ions. Biometeorology pollutants by tree species. Urban Environment & Urban Ecology 29(3):205. 15(2):7-9. 5Nakane, H., Asami, O., Yamada, Y. and Ohira, H. 2002. Effect of negative 25Shang, D., Li, Z. and Li, C. 1991. Poplar,Beijing peach, lilac leaves of air ions on computer operation anxiety and salivary chromogranin A- heavy metal pollutants in the atmosphere, Cu, Cr, Pb, Zn purification like immunoreactivity. Int. J. Psychophysiology 46:85-89. potential to explore. Environmental Protection Science 17(3):71-75,57. 6Vartiainen, E., Kulmala, M., Ehn, M., Hirsikko, A., Junninen, H.,Petäjä, 26Chen, X.,Xie,Y. and Peng, Z. 1997. Relationship between air pollution T., Sogacheva, L., Kuokka, S., Hillam, O ., Skopokhod, A., Belikov I., and contents of metal elements in leaves of urban plants. Urban Elansky, N. and Kerminen, V. 2007. Ion and particle number Environment & Urban Ecology 10(1):45-47. concentrations and size distributions along the trans-Siberian railroad. 27Lu, M., Li, Y. and Qi, X. 2003. Comparison of ability of plant Boreal Environment Research12:375-396. remediation for air pollution. Journal of Shandong Institute of 7Tammet, H., Horrak, U. and Laakso, L. 2006. Factors of air ion balance Architecture and Engineering 18(4):44-46. in a coniferous forest according to measurements in Hyytiälä, Finland. 28Fang, Y. 2006. Functional Studies of The Ecological Environment of Atmospheric Chemistry and Physics 6:3377-3390. The Urban Forest Green. PhD dissertation,Nanjing Forestry 8Venzac, H., Sellegri, K. and Laj, P. 2007. Nucleation events detected at University, pp. 43-48. the high altitude site of the Puy de Dome Research Station, France. 29Xiong, H. and Qin, S. 2006. Estimating the economic values of the Boreal Environment Research 12:345-359. forest ecosystem service function in XinJiang. Journal of Arid Land 9Daniell, W., Camp, J. and Horstman, S. 1991. Trial of a negative ion Resources and Environment 20(6):146-151. generator device in remediating problems related to indoor air quality. 30Yang, B.S., Zhao, T.Q., Yin, G. Q., Zheng, H., Ouyang, Z.Y. and He, P. Journal of Occupational Medicine and Environmental Medicine 12:256- 2006. The research of Zhangjiajie scenic ecosystem services change 269. in1990-2000. Forest Research 19(4):517-522. 10Reiter, R. 1985. Frequency distribution of positive and negative small 31Sun, H. and Zhu, N. 2008. Ecological functions of tree species used in ions concentrations, based on many years recording at two mountain urban afforestation in Harbin City. Journal of Chinese Urban Forestry stations located at 740 and 1 780 m asl. Int. J. Biometeor 29(3):223- 6(5):54-57. 225. 32Tao, L., Ren, J., Du, Z. and Hou, P. 2008. Dust-holding effects of major 11Ye, C., Wang, X. and Guo, W. 2000. Air concentration of negative ions landscaping tree species in Lanzhou city. Journal of Chinese Urban in the relationship between meteorological exploration. Meteorological Forestry 6(4):55-57. Science and Technology 4:51-52. 33Liu, Y. and Sun, Z. 2008. The dust removal measurement of part of tree 12Wu, C., Zheng, Q. and Zhong, L. 2001. A study of the aero-anion species in Jilin City. Journal of Jilin Agricultural Science and Technology concentration in forest recreation area. Scientia Silvae Sinicae 37(5):75- College 17(2):4-5. 81. 34Cheng, Z., Wu, J., Liu, Y., Li, H., Xiong,Y., Li, H. and Li, L. 2004. 13Liu, K., Su, S., Jiang, J. and Xu, W. 2002. Investigation of anion content Effects of main afforestation tree species on dust blocking in Yueyang of environment on some types of vegetation. Forestry Science and City. Journal of Chinese Urban Dorestry 2(2):37-40. Technology 18(2):37-39. 35Hu, X., Yin, A., Wu, X. and Lu, Y. 2007. The selecting of superior dust 14Wang, C. 2003. The Huangshan Scenic Anion Tourism Resources detention tree species in modern urban forestry of Pearl River Delta. Distribution Causes and The Development and Utilization of Research. Guangdong Landscape Architecture 3:44-46. MSc thesis, Anhui Agriculture University, pp. 35-38. 36Li, B. and Tao, S. 2000. Surveying and analysis of traffic noise from 15Shao, H., He, Q., Yan, H., Hou, Z. and Li, T. 2005. Spatio-temporal main urban roads of Beijing. Urban Environment & Urban Ecology changes of negative air ion concentrations in Beijing. Journal of Beijing 13(2):11-13. Forestry University 27(3):35-39. 37Liu, Z. and Chen, G. 2002. Turfgrass Varieties Guide. China Industry 16Wu, Z., Wang, C. and Xu, J. 2007. Air-borne anions and particulate Press, Beijing, 7 p. matter in six urban green spaces during the summer. Journal of Tsinghua 38Zhu, Z. 1992. Environment and Ecological Protection Science. China University (Science and Technology) 47(12):2153-2157. Forestry Publishing House, Beijing, 8 p. 17Meredith, M. L. and Hites, A. 1987. Polychlorinated biphenyl 39Huang, Y., Chen, D., Lu, D. and Lu, Y. 2004. Air negative ion and city accumulation in tree bark and wood growth rings. Environ. Sci. Techno1. environment. Arid Environmental Monitoring 18(4):208-211. 21:709-712. 40Shi, Q., Zhong, L. and Wu, C. 2002. Grades standard of aeroanion 18Trapp, S., Miglioranza, K.S. and Mosbaek, H.2001. Sorption of concentration in forest surroundings. China Environmental Science lipophilic organic compounds to wood and implication for their 22(4):320-323. environmental fate. Environ. Sci. Techno1. 35:1561-1566. 41Zeng, S., Sun, Z. and Chen, B. 2006. Review on forest negative air ions 19He, Y., Zhang, D., Zheng, W., Gao, Y. and Xu, I. 1997. Effects of air in China. Journal of Nanjing Forestry University (Natural Sciences

pollution from industrial waste gas-Cl2 and SO2 on chlorophyll content Edition) 30(5):107-111. on leaves of Northeast ordinary trees. Journal of Qiqihar Teachers’ 42Liao, Z. 2007. Air negative ion and air quality. Chemistry Teaching College (Natural Science) 17(1):56-58. 11:56-58. 20Sun, Z., Bai, Y. and Wang, P. 1998. Study on the plant based fluoride monitoring of polluted atmosphere. Environmental Monitoring In China 14(2):11-14. 21 Luo, H., Li, J. and Liu, Z. 2000. Effect of purifying SO2 in atmosphere by greening tree species. Journal of BeiJin Forestry University 22(1):45-50. 22 Han, S. 2001. Studies on potentials of purifying SO2 by main trees in areas. Journal of Liao Ning University (Natural Sciences Edition) 28(2):174-179. 23Zhang, C., Qi, Q., Ji, H. and Li, W. 2001. Dertermination of heavy metals and sulfur in poplar leaves of the main traffic road and study on atmosphere pollution state in BeiJing. Journal of Beijing Normal University (Natural Science) 37(5):795-799. 24Lu, M., Li, Y. and Lu, J. 2002. Absorption and purification to main air

1254 Journal of Food, Agriculture & Environment, Vol.11 (2), April 2013