Study On The Impact Of Urban Waterfront Green Space On Atmospheric Particulate Pollution And Microclimate

Air particle pollution and the"heat island effect"in some cities of China are serious,and urban waterfront green spaces have turned out to be ecological beneficial and have important practicability.In order to explore the differences in the impact of different models of waterfront green space on mitigating air pollution and improving the microclimate,we compared the ability of purifying air and regulating the microclimate produced by different average tree height?high?>9m?,medium?5-9m??,Low?<5m?)and different canopy-closures?high?>0.7?,medium?0.4-0.7?,low?0.2-0.4??.PM_2.5and PM₁₀concentration,temperature,relative humidity,wind velocity were monitored simultaneously during daytime?7:00-19:00?for three days in January,April,July and October of 2019,and temperature-humidity index was used to evaluate human comfort degree so as to select waterfront greenbelt models with better ecological benefits.The main findings are as follows:?1?In terms of PM_2.5concentration daily change,the trend in spring and autumn were similar with rapid decline-basic stability-slow rise and wavelike rise-decline-rise in summer and winter.The reduction effect of green spaces with high average tree height and high canopy density and high average tree height and medium canopy density was better.The average rates were 26.59%and 26.24%,respectively.The daily concentration in summer reached the lowestand met the first standard while in three other seasons met the second standard.On the contrary,the reduction effect of green space with low tree average height and medium-canopy was the worst and reached thein summer,which still met the first standard.The annual PM_2.5concentration of all sites did not reach the second standard.The daily variation of PM₁₀concentration in four seasons were similar,showing a trend of decline-basic stability-rapid rise.In terms of reduction effect,the plots with high average tree height and high canopy density and high average tree height and medium canopy density were still the most significant,with average reduction rates of24.93%and 26.43%.In summer the concentration was the,which meet the first standard.The site with low-average tree height and low-canopy still had the worst reduction effect,but met the first standard in summer with.Only the annual PM₁₀concentration in four sites with higher average tree height and canopy density met the second standard.?2?As for the four microclimatic elements in the four seasons:temperature rose first and then decreased;relative humidity decreased first and then rebounded,the change in winter was the smallest.There was no obvious peak in daily wind speed except spring,but there were many small fluctuations.In terms of adjusting microclimate,the green space with high average tree height and medium-canopy got the most remarkable effect,it's average cooling efficiency was 22.63%;average humidification efficiency was 23.96%;average reduction rate of wind velocity was 23.96%;the grades of human comfort degree were“cold”,“comfortable”,“hot”and“very cold”in spring,summer,autumn and winter respectively.In contrast,the green space with low average tree height and low-canopy had significant effect,the significance was the lowest,and the grades of human comfort degree were“comfortable”,“sultry”,“hot”and“very cold”.?3?All the waterfront spaces with arbor-shrub-grass mode could significantly reduce the air particulate concentration and improve the microclimate to a certain degree in the four season.The green spaces in structure of arbor-shrub-herb type with average tree height?>9.7m?and canopy density?>0.61?have the highest efficiency in reducing PM_2.5and PM₁₀concentration,improving the microclimate and benefiting people's outdoor recreation.