城市道路绿化带"微峡谷效应"及其对非机动车道污染物浓度的影响

研究不同绿化带结构对非机动车道污染物浓度的影响,将为城市道路绿化带格局提供依据。利用遮荫网模拟10、20、30 m隔离的道路绿化带,并模拟了3种不同结构的绿化带,分别对各类道路微气候条件(风)及SO₂、NO_x、NH₃、总悬浮颗粒物(TSP)和可吸入颗粒物(PM10)等5种主要污染物浓度进行了观测。结果表明:风速小于2 m/s时,10 m和20 m间隔的道路绿化带会产生"微峡谷效应",使绿化带间隔内风速增加。10 m间隔的绿化带较其它两种绿化带对各种污染物的净化百分率更明显,且污染物净化百分率与风速大多正相关显著。12.5 m的模拟绿化带与10 m的间隔交替的绿化带可以更有效地降低非机动车道的污染物浓度,污染物净化百分率与风速也大多正相关显著。不同结构道路绿化带会影响道路微气候条件,从而影响非机动车道污染物浓度。城市道路绿带存在合理的绿带结构,可以通过设计更合理的城市道路绿带模式有效改善城市非机动车道空气质量。

"Micro-canyon effect" of city road green belt and its effect on the pollutant concentration above roads for non-motorized vehicles

The present experiment investigates the effect of the green belt structure on the pollutant concentration above roads for non-motorized vehicles and provides a basis for designing a road green belt pattern. We simulated green belts separated by 10, 20, and 30 m intervals with shade cloth. The three simulations were of 10 m roads alternating with 10 m green belts, 10 m roads alternating with 12.5 m green belts, and no roads in an 80 m green belt. Microclimate (wind) conditions and the concentrations of five major pollutants, namely SO₂, NO_x, NH₃, total suspended particles (TSP) and respirable particulate matter (PM10), were observed for all types of road. The observation periods were from 7 to 8 am, from 9 to 10 am, from 11 am to 12 pm, from 1 to 2 pm, and from 3 to 4 pm on the same day. The results show that when the wind speed was less than 2 m/s, the green belts separated by 10 m and 20 m intervals had a "micro-canyon effect", and the wind speed above the green belt interval increased by 23.33% and 20.22%, respectively, whereas the wind speed above green belts separated by 30 m reduced by 3.33%. When the wind speed exceeded 2 m/s, none of the green belts displayed a micro-canyon effect. There was a nonlinear relationship between increasing the interval width and the percentage removal of pollutants, with the green belts at 10 m intervals having the greatest effect. When the wind speed dropped below 2 m/s, for the 10 m interval, the daily average percentage removals of the five pollutants SO₂, NO_x, NH₃, TSP and PM10 were 32.01%, 29.43%, 7.66%, 54.27% and 53.90%, respectively. When the wind speed exceeded 2 m/s, for the 10 m interval, the daily average percentage removals of the pollutants were 16.50%, 16.90%, 12.02%, 32.86% and 25.14%, respectively. It was also found that the percentage removal of the five pollutants had positive correlation with the wind speed for the 10 m interval but not for the 20 m and 30 m intervals.The structure of 12.5 m green belts at 10 m intervals can more effectively reduce the pollutant concentration of roads for non-motorized vehicles; the daily average percentage removals of the pollutants were 8.74%, 9.13%, 7.63%, 13.01% and 15.56% when the wind speed was less than 2 m/s and 7.03%, 3.51%, 10.4%, 24.35% and -14.28% when the wind speed exceeded 2 m/s, respectively. The positive correlations between the removal percentages of the pollutants and the wind speed were the most significant for this green belt mode. The removal percentages of pollutants were small or negative for other green belt modes. The green belt structure affects the micro-climatic conditions of the road and thus the pollutant concentration over roads for non-motorized vehicles. Applying a reasonable structure for the urban road green belt, we can improve air quality over roads for non-motorized vehicles.