Pollution Characteristics Of PM_2.5 And Its Driving Differences In The Beijing-Tianjin-Hebei Region

In recent years,the economic model of“high energy consumption,high pollution&high emission”has caused many environmental problems in various regions of China.The Chinese government attaches great importance to ecological and environmental protection,adheres to the belief that“Lucid waters and lush mountains are invaluable assets”,initiates harmonious coexistence between human and nature,and adheres to the road of green and sustainable development.Air pollution,especially PM_2.5 pollution,has brought huge health risks and economic costs to China,and is an important obstacle to sustainable development of China.The serious PM_2.5 pollution has attracted extensive attention from the public,and the scientific establishment of the relevant understanding of PM_2.5 pollution in cities has become one of the hotspots in the research of urban ecological security and sustainable development.At the same time,the different natural and socioeconomic development of cities in the region has brought the unique background of each city to a large extent,which may make the interpretation of the relationship between urbanization and environmental risk uncertain.In this context,the Beijing-Tianjin-Hebei（BTH）region,one of the most economically developed regions in China,is selected as a typical study area.The following studies are mainly carried out:an index system that may affect PM_2.5 pollution in the BTH region was constructed based on scientific,systematic and feasible principles at the first.Secondly,from the perspectives of temporal variation,spatial dependence and spatial differentiation,hourly PM_2.5 concentration data from national air quality monitoring stations from 2014 to 2018 were used to analyze the spatiotemporal patterns of PM_2.5 pollution in the BTH region by using the Mann-Kendall test,spatial autocorrelation analysis and spatial hot spot analysis.Finally,we use the stepwise regression and the optimal curve fitting method to explore the driving factors affecting PM_2.5pollution in the whole BTH region and various cities,as well as the potential differences of air pollution driving factors among cities.And the research results were discussed in detail,to deepen the understanding of the relationship between natural,socioeconomic factors and air pollution.The results showed that:（1）From 2014 to 2018,PM_2.5 concentration in the BTH region decreased year by year from94.24μg/m³ to 54.94μg/m³,and air pollution improved significantly.And the average annual PM_2.5 concentration decreased in all cities,with the largest decline in Baoding（48.17%）and the smallest decline in Zhangjiakou（10.53%）.The seasonal average PM_2.5 concentration showed a U-shaped trend with the change of seasons.PM_2.5 pollution was the most serious in winter and relatively light in summer.The decrease of PM_2.5 concentration in different seasons was 44.62%in summer,42.83%in autumn,29.10%in spring and 23.09%in winter.（2）The spatial distribution of PM_2.5 pollution in the BTH region showed significant aggregation characteristics and regional differences.The pollution of the southwest cities（Baoding,Shijiazhuang,Xingtai and Hengshui）was serious,and north cities（Zhangjiakou,Chengde and Qinhuangdao）were light.At the same time,the regional pollution showed a strong spatial dependence,with the strongest autocorrelation of PM_2.5 spatial distribution in winter.The interaction between cities in the region is obvious,and the joint prevention and control of regional pollution are of great significance.（3）The socioeconomic factors contributed more to PM_2.5 pollution than natural factors.Among them,green area and population density were the most important negative and positive driving factors of PM_2.5 pollution in the whole region respectively,and the proportion of urban population was the second negative driving factor.Therefore,green urbanization is the primary path of regional sustainable development.In addition,the most important driving factors of PM_2.5pollution in all cities were socioeconomic factors,and the main driving factors of PM_2.5 pollution in different cities in the BTH region were heterogeneous.Urban built-up area,amount of patent application authorization,greening coverage rate of built-up area,the proportion of urban population,proportion of secondary industry in GDP,area of urban construction land,road freight volume,the proportion of urban population,emission of industrial smoke（powder）dust,area of urban construction land,the proportion of primary industry in GDP and per capita disposable income are the key influencing factors of pollution in Beijing,Tianjin,Shijiazhuang,Tangshan,Qinhuangdao,Handan,Xingtai,Baoding,Chengde,Cangzhou,Langfang and Hengshui,respectively.This shows that there are significant differences in the contribution of various factors to pollution in different cities,and specific pollution prevention and control plans should be formulated for different cities.（4）The relationship between air pollution and relative humidity,built-up area,green area,area of city paved roads at year-end,the volume of industrial SO₂ emission,population,population density,the proportion of the primary industry in GDP in the BTH region met the Environmental Kuznets curve（EKC）hypothesis.PM_2.5 pollution has a linear correlation with average wind speed and urban construction land area.And there is a power function relationship between PM_2.5pollution annual public transport passenger volume and housing construction completed area.