| In this study,367 cities were taken as research objects,and cluster analysis was used to divide the urban agglomeration.The spatial and temporal distribution characteristics of air pollution were explored from the perspective of urban agglomeration.The correlation between atmospheric particulate matter and gaseous pollutants in different urban agglomeration was analyzed to clarify the air pollution characteristics of different urban agglomeration.The regional transport characteristics were analyzed to compare the regional transport characteristics of different urban agglomerations,and the blocking adsorption capacity and mechanism of plants on PM2.5 were quantitatively studied to explore effective air pollution treatment methods for different urban agglomerations.The conclusions are as follows:(1)In terms of inter-annual changes,the concentrations of PM2.5,PM10,SO2 and NO2 decreased in 2016,while the concentrations of O3 and CO increased.PM2.5,SO2 and NO2 concentration values have the highest reduction rate in northeast city clusters,while PM10 has the highest reduction rate in northern coastal city clusters.In terms of seasonal distribution,the overall seasonal characteristics of atmospheric pollutant concentration are winter>autumn>spring>summer.In terms of monthly variation,PM2.5 and PM10 show "u-shaped" monthly variation characteristics;CO and SO2 show "deep U" monthly variation trend in heating season in city clusters with central heating.The highest O3 values usually occur in June and July.In terms of daily variation,the daily variation of PM2.5 and PM 10 concentrations reaches the highest value at 10-14 points and the lowest value at 16-20 points.The diurnal variation characteristics of SO2,NO2 and CO are similar,showing "bimodal and double valley"variation characteristics,while O3 shows "single peak and double valley" characteristics.(2)In the spatial distribution,the concentration of SO2 and NO2 in the provincial capital cities is relatively high in the urban agglomeration in northeast China.The concentrations of SO2,NO2 and CO were higher in the northern coastal city clusters,southern Hebei province and Shandong province.Among the city clusters on the east coast,the pollution of atmospheric particulate matter and SO2 in Jiangsu province is serious,and the pollution of NO2 in Shanghai is serious.In the southern coastal urban agglomeration,controlling air pollution in guangdong-hongkong-macao greater bay area and Henan province is the key to controlling air pollution in the regional urban agglomeration.In city clusters in the middle reaches of the Yellow River,reducing coal burning in Shanxi to reduce SO2 and CO emissions is the key to improving regional air pollution.Cities in the middle reaches of the Yangtze River,centered on Wuhan,yichang and Hefei,are the most polluted.In the urban agglomeration of southwest China,the emission control of atmospheric particulate matter and NO2 in the Sichuan basin is particularly important for the improvement of air pollution.In the urban agglomeration of northwest China,the control of air pollution should strengthen the control of land desertification and reduce the pollution of sand and dust.There is a strong correlation between pollutants in urban agglomerations,and SO2 plays a more obvious role in regional transmission and exchange between urban coastal urban agglomerations.(3)The northern coastal city clusters and the eastern coastal city clusters are the most seriously affected by regional transmission.From the perspective of urban types,island cities are the most seriously affected by regional transmission.Airflow from the south of Beijing is the main transmission channel of PM2.5;airflow from the west and northwest is the main transmission channel of PM10;airflow from the northwest has the highest concentration of SO2 and NO2;airflow from the northeast is conducive to the production of CO;airflow from the south of hebei and shandong causes the rise of O3 concentration.Southern Hebei province and Shandong province are the most important potential sources of PM2.5 in Beijing.Potential sources of PM10 include southern Hebei province,southwest Shandong province and Shanxi Province.Southern Hebei,Shandong,Henan and Shaanxi provinces are potential sources of SO2.Potential sources of NO2 include southern Hebei province,Shandong province and Shanxi Province.The CO region transfers less.Potential sources of O3 are located in southern Hebei,Shandong and Shanxi provinces.Over the past decade,PM10 contributions in Shandong,Tianjin and Henan provinces have increased,while those in Inner Mongolia and Mongolia have declined.(4)Cunninghamia lanceolata has the strongest ability to absorb PM2.5 per unit leaf area of tested tree species.And the weakest adsorption capacity is Ginkgo biloba.Due to the large difference in leaf area between tree species,the total amount of PM2.5 adsorbed by tree species also varies greatly.Among them,Cunninghamia lanceolata is the tree species with the strongest ability to block and adsorb PM2.5.The species with an adsorption capacity of more than 100mg are Litsea elongata,Pinus massoniana,Pinus armandii Franch,Broussonetia papyrifera,Erythrina variegata,Koelreuteria bipinnate and Ficus microcarpa.Overall,the adsorption capacity of conifer species was stronger than broadleaf species.There was a significant positive correlation between the unit leaf area blocking the adsorption of PM2.5 and the ratio of grooves and the number of leaf hairs.There was a significant correlation between stomatal size and the amount of PM2.5 blocked by adsorption.The correlation coefficient of smaller stomata was larger than that of the group with larger stomata.The larger stomatal size was,the smaller the inhibitory effect on the ability of blocking adsorption of PM2.5 was.The ability of tree species in Beijing to block the absorption of PM2.5 is stronger than that in Chongqing,which may be because the same tree species has more leaf hairs,larger ratio of grooves,and stomatal size and stomatal density in Beijing than in Chongqing. |
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