| PM2.5 is the primary air pollutant that impacts on human health seriously in Beijing.Plant leaves with special surface structure and properties of the particles that have PM2.5 blockages,adhesion and absorption capacity and plays important role on commanding PM2.5 pollution in the atmosphere.By analyzing the relationship between PM2.5 mass concentration and meteorological factors in different forestry areas,this research determines the urban forest environmental factor's influence pathway,degree and process and dynamic effects of PM2.5;Determined and quantified PM2.5 absorption amount and the microscopic characteristics of the common green tree leaf surface,explanation effect of leaf microscopic characteristics difference and PM2.5 absorption amount;By determining and analyzing variation on leaves' PM2.5 absorption and it's affecting factors in rainfall weather,we find out different tree species' influences that determined by rainfall differences.And we explore plant leaves' PM2.5 was cleaned,which requires rainfall,rainfall intensity and the time required to leaves' PM2.5 absorption quantity arrives saturated;to obtain the PM2.5 adsorption amount of different tree species configuration mode,clarify PM2.5 reduction effect and differences of the different plant configuration mode.The results can provide data support for the city atmospheric PM2.5 deposition process,it has important guiding significance to clarify the urban forest reduce pollution function and urban forest plant control PM2.5.The main conclusions are as follows:From 2016 to 2017,the mean value of PM2.5 mass concentration in vegetation area and non-vegetation area showed that the diurnal variation of PM2.5 mass concentration in vegetation area was bimodal and double-valley type,which was smaller than that in non-vegetation area.Both vegetation and non-vegetation areas showed the same variation pattern.The PM2.5 mass concentrations in both vegetation and non-vegetation areas decreased from 2016 to 2017.In different months,the PM2.5 concentrations in the vegetation and non vegetative areas were larger in January and March.The PM2.5 concentrations in the vegetative and non vegetative areas were smaller in August,and the seasonal variations were winter > spring > autumn > summer.The PM2.5 mass concentration is higher in vegetation area than in non-vegetation area in the process of precipitation,windy,high temperature and high humidity weather,indicating that the air quality in vegetation area is better than that in non-vegetation area,and the forest can pull the pollutants around it.The pollutant is absorbed and accumulated in it,the precipitation and gale are helpful to reduce PM2.5,the change of PM2.5 mass concentration inrain and gale weather has no lag,the change before and in rain is bigger,and the change after rain is small.The PM2.5 mass concentration decreased to the lowest value at 24 hours after rain and one day after wind,and the decrease of PM2.5 concentration was more obvious in forest vegetation area after rain,but the fluctuation of PM2.5 mass concentration was relatively small in windy weather.The PM2.5 adsorption capacity per unit leaf area was as follows: October(0.618±0.16?g·cm-2)>September(0.514±0.14?g·cm-2)>July(0.509±0.14?g·cm-2)>Aug ust(0.487±0.12?g·cm-2)>June(0.464±0.08?g·cm-2)>May(0.359±0.08?g·cm-2)in different month;the annual average of PM2.5 adsorption capacity per hectare was as follows: Pinus tabulaeformis(4.079 ± 0.13 kg·hm-2·a-1)> Platycladus orientalis(3.259 ± 0.14 kg·hm-2·a-1)> Sabina chinensis(3.095±0.15kg·hm-2·a-1)>Picea asperata(2.797±0.13kg·hm-2·a-1)>Robinia pseudoacacia(1.825±0.12kg·hm-2·a-1)>Acer elegantulum(1.805±0.13kg·hm-2·a-1)>Poplus alba(1.695±0.12kg·hm-2·a-1)>Betula platyphylla(1.444±0.16kg·hm-2·a-1)>Padus maackii(1.398±0.13kg·hm-2·a-1)>Quercus mongolica(1.221±0.11kg·hm-2·a-1).The leaves of Pinus tabulaeformis and Platycladus orientalis have folded leaf lamina and are covered by fine hairs.Therefore,their roughness is relatively high,with many protrusions and fillisters on the leaf surface.Roughness is higher on the leaves.Pinus tabulaeformis and Platycladus orientalis PM2.5 absorption capacity is higher than that of Betula platyphylla and Quercus mongolica,which have smooth leaves and mostly oblong stomata.The ranking of average roughness of the leaves was as follows: Pinus tabulaeformis?763.33±131.83nm?>Platycladus orientalis?432.67 ± 53.21nm?> Sabina chinensis?409.33 ± 95.72nm?>Picea asperata?399.67 ± 62.70nm?> Robinia pseudoacacia?378.00 ± 89.54nm?> Acer elegantulum?366.33 ±106.04nm?> Poplus alba?346.33±53.90nm?> Betula platyphylla?340.00±79.64nm?>Padus maackii?271.33±97.56nm?>Quercus mongolica?170.33±68.20nm?.This accorded with PM2.5 adsorption per unit leaf area,and leaf roughness had a significant positive correlation with PM2.5 adsorption capacity per unit leaf area as well?R2=0.706?.To improve the environmental effects of city vegetation air quality,tree species with leaf surface morphology that facilitates absorption of PM2.5 and other particles should be selected.During the daytime period of 7:00-17:00,the diurnal variation of PM2.5 mass concentration was the largest at 7:00 in different plant allocation modes,and the daily mean value of PM2.5 mass concentration in different plant allocation models was the highest in needle mixing,followed by mixed arbor and shrub.The adsorption capacity of PM2.5 per unit leaf area in different plant allocation patterns of broad-leaved pure forest in May and October was as follows: coniferous mixed forest > arbor and shrub mixed > Pure coniferous forest > coniferous and broadleaved mixed forest > broadleaved mixed forest> Pure broadleave forest,and Pure coniferous mixed forest was 1.83 times as high as broad-leaved pure forest.The amount of PM2.5 adsorbed by coniferous mixed with different plant allocation patterns was the largest,and the adsorption amount of PM2.5 by pure forest was smaller,especially inbroad-leaved pure forest.According to different plant allocation models,the corresponding tree species and plant combinations can be planted according to the PM2.5 adsorption amount per unit leaf area in order to effectively reduce air pollutants. |
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