| With the development of urbanization,the phenomenon of the air pollution is becoming more and more serious,and the fog and haze weather continuously increased not only affects people's travel,but also brings serious harm to people's health.Moreover,the atmospheric particulates has become one of the main air pollution sources.Now,how to reduce atmospheric particulates has become one of the most technical problems in the construction of beautiful towns.Because Forest vegetation plays an important role in reducing atmospheric particulates,Therefore,all walks of government has been paid more and more attention to establishment of forest cities.However,How is the function of the urban forests to suppress dust and smog? What kind of the forest structure is the best? Now,there is no in further study.So,In this paper,we take the 12 kinds of typical structure and configuration of the road forest in Tai'an as the research object,Meanwhile we were synchronously monitored the 4 kinds of particles inside the road forest,it's TSP,PM10,PM2.5 and PM1.Order to explore the trend of changes in different seasons,periods and levels of gradient and analyze the function dust removal of the different configuration patterns of the city road forest,which will provide theoretical basis for the construction of city environmental friendly road forest.The results are as follows:(1)Diurnal variation of atmospheric particulate trend influenced by human activitiesThe TSP,PM10,PM2.5 and PM1 daily variation trend was approximately high in the morning and evening,and it was similar to the “U” shape.The peak value of atmospheric particulate appeared in the morning peak(8:00)and evening peak(18:00)periods of human activities.The concentration of atmospheric particulates was low at 10:00 and 16:00.TSP PM10,most of the time period can reach secondary standard of environmental quality,8:00 two particles in highest concentration were 473.49?g/m~3,214.39?g/m~3 respectively,beyond the environmental quality standards of the two 36.6%,30%;followed by 18:00,which exceeded 7.36%,16.53%.PM2.5 8:00 and 18:00 to achieve air quality two level standard,and the two time periods it's were exceeded ambient air quality level one class standard 29.3% and 13.4%,and the rest of the time period can basically reach the one class level standard.So,It is advisable for the urban residents to avoid outdoor activities as early as possible in the morning and evening.(2)The effect of urban road forest on atmospheric particulates reduction in different seasonsIn different seasons,the variation trend of atmospheric particles is the same,Obviously,the highest seasons is winter,and higher than other seasons,followed by autumn,spring and summer.In the summer,the TSP and PM10 were 156.91?g/m~3,53.73?g/m~3,it's reached to air quality to level standard.In spring,autumn and winter respectively in the mean TSP beyond the air quality level two standard 23.5%,41.65%,86.6%,PM10 concentrations exceed air quality standards of the two 45.05%,68.59%,94.16%,it's indicate the two kinds of particles in winter is most polluted.The PM2.5 concentrations were 28.81?g/m~3,15.62?g/m~3,which reached air quality two level standard in spring and summer,However autumn and winter respectively exceed the standard72.5%,87.6%.The ability of road forest to reduce atmospheric particulates in different seasons is different,that in spring and summer,there is a reduction effect on Atmospheric Particulates,But the effect is not obvious in winter in autumn,and in winter,the concentration of particulate matter in forest is higher than that in forest,The TSP,PM10,PM2.5and PM1 increased by 111.56?g/m~3,116.99?g/m~3,23.88?g/m~3,2.53?g/m~3 in winter.Increase in particle concentration is also the main cause of haze,so,in autumn and winter we should control the number of cars,in order to reduce automobile exhaust emissions.In addition,we also should increase the proportion of conifer species in road forest,Even if the leaves fall in autumn and winter,they can also purify the atmospheric particulates(3)Correlation between atmospheric particulates and meteorological factorsIt is found that the meteorological factors have great influence on the air particulates,and the relative humidity,wind speed and wind direction are the main factors affecting the concentration.The wind speed and the particles are linearly negative,and the wind can effectively diffuse the air particles in the forest belt.Affected by different weather conditions,temperature and air particles are not significant correlation;the relative humidity and air particles are linear positive correlation;the higher the relative humidity,the higher the concentration of air particles.(4)The horizontal spatial variation of atmospheric particulates in urban road forestIn the clear breeze and sunny weather after rain,the atmospheric particulates of each monitoring point inside the road forest was lower than that of the control point,and the decrease was most obvious at 30 m.The maximum decrease of TSP,PM10,PM2.5 and PM1 was 21.7%,15.81%,25.53% and 27.4% respectively.The cloudy and fog and haze weather,road forest of air particulate matter control ability is weak,only at 30 m TSP and PM10 were reduced by 2.77% and 5.64%,but showed a more wide belt,abatement of air particulate matter characteristics of the stronger.Based on this,considering the limitations of the road green belt width in the road and the red line of the road,it is recommended that the width of road forest construction be at least 20 m.(5)Optimal allocation model for urban road forest to reduce atmospheric particulatesThe difference of different configuration mode of road forest dust removal belt of air particulate matter significantly correlated with plant species,vegetation quantity,structure and other factors.The atmospheric particulates dust removal in which the strongest coniferous shrubs and forest structure,single structure of the road effect is the worst.The abundant plant species,complete and abundant volume of green plants can make the community play more dust removal.Through the 12 different configuration mode of road dust retention ability of forest evaluation,we selected 4 kinds of dust removal and ornamental effect good configuration mode,as follows:(1)Coniferous and broad-leaved mixed type,mixed with 4 ~ 6 tree species with Cedrus deodara and Prunus cerasifera and so on.The ratio was 1: 1 and the proportion of native tree species is more than 80%.(2)Needle leaf forest type: Cedrus deodara,Pinus tabulaeformis and other 3 to 4 kinds of coniferous trees as the dominant species mixed,the proportion of native tree species 90%.(3)Natural type: The big trees Platanus orientalis and Sophora japonica,Prunus cerasifera,small trees and other shrubs mixed,the proportion of native trees more than 60%.(4)Egular arrangement: Berberis thunbergii DC.f.atropurpurea Rehd.,Sabina chinensis and other shrubs and lawns accounted for about 50%,large trees,sub-tree species to Koelreuteria paniculata,Lagerstroemia indica,evergreen than deciduous at least 1: 3. |
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