Research On The Relationship Between Regional Urbanization And PM_2.5 Spatiotemporal Evolution Based On Nighttime Light Data

China's economic construction and urban progress apace,the carry forward of urbanization has brought us abundant material and diversified cultural conditions,affecting multiaspects of life,improve people's yearning for a better life.However,there is a time gap between the changes in various aspects and the development of environmental protection awareness.Air pollution contributes most immediately to environmental pollution,among which PM_2.5pollution is the typical one,which interferes with people's production and life and endangers their health.In the process of PM_2.5formation,urbanization can be regarded as an inductive factor,stimulating the formation of positive pollution indicators.Therefore,it is not necessary to explore the relationship between PM_2.5pollutant concentration and regional urbanization.Located in southwest China,Sichuan and Chongqing include two new first-tier cities--Chengdu and Chongqing.As the economic center of southwest China,the economic development radiates and drives five provinces and cities in southwest China.The"Chengdu-Chongqing City Group"contained in the region is also a focal point investment region of the state.In the process of urbanization development,Cheng-Chongqing area is gradually affected by PM_2.5pollution,which has seriously reduced people's happiness index.Clarifying the spatial characteristics of pollution and the influence of regional urbanization on pollution is vital to the realization of the dual objectives of economic growth and preservation of environment in Sichuan and Chongqing area.Beginning with the spatial and time dimensions,this paper first introduces the idea of"entropy"to establish the relationship between multi-dimensional urbanization statistics panel data and spatial DMSP/OLS luminous image data.Then,the methods of urban expansion thought and cold-hot spot analysis,standard deviation ellipse analysis and regression model analysis are introduced to analyze the space-time relationship between the luminous image data set and PM_2.5average concentration raster data,and indirectly establish connection between regional urbanization and PM_2.5concentration division.Finally,the methods of geo-detector analysis and landscape pattern analysis are introduced to further identify the urbanization factors and the degree of influence on PM_2.5.Studying the relevance between PM_2.5concentration and urbanization can provide reference for regional air pollution control and protection,and also promote people's understanding and concern about the relationship between environment and city.The main results of the study are as follows:(1)Adjusted DMSP/OLS night light image data is suitable for the urban development of Sichuan and Chongqing,and the average night light index evaluates and reflect the urbanization level better.The extraction results of urban built-up areas are consistent with the actual distribution,which can visualize the distribution of urban space-time.(2)PM_2.5concentration in the central,eastern and southern regions of Sichuan and Chongqing concentrated,and the peak area was located in the main city of Chengdu-Chongqing,and the Chengdu-Chongqing urban agglomeration had high concentration.The western and northeastern parts of Sichuan are less affected by PM_2.5pollution,while the Aba Tibetan Autonomous Prefecture is basically unaffected by the pollution.The pollution center is stable in Ziyang City and Suining City,and the pollution scope shows a fluctuating trend,but the overall trend of expansion.(3)The multi-scale nighttime light data was used to explore the relationship between regional urbanization and PM_2.5pollution.An in-depth analysis of the impact of urban development on PM_2.5pollution in Sichuan and Chongqing showed that there was a significant correlation between the two at the municipal level and a high goodness of fit at pixel level,county level and urban agglomeration level.The geographically weighted regression model(GWR)has higher fitting degree than the least square regression model(OLS),and both of them have spatial nonstationarity.Areas with high fitting degree tend to be those with both high urbanization level and high PM_2.5concentration.(4)Geodetector analysis and landscape pattern analysis further explore what regional urbanization factors affect PM_2.5concentration distribution and how?It was found that nighttime light and per capita gross domestic product(GDP)had strong explanatory power for PM_2.5concentration.The rapid growth of urban population causes the fluctuation of PM_2.5concentration;The vigorous development of secondary and tertiary industries may pay more attention to environmental protection and have a inhibiting effect on PM_2.5pollution.Extensive urban expansion continues,and green coverage in built-up areas has a continuing impact on PM_2.5pollution concentration.The greater the type of urban construction land,the more serious the PM_2.5pollution will be.As cities become more fragmented and complex,PM_2.5concentrations also increase.