Research On Remote Sensing Estimation Of PM_2.5 Concentration And Its Interaction With Urbanization In The Yangtze River Delta

Since the 1980s,China has experienced the high speed development of economy and urbanization.However,the rapid development of urbanization has exerted some negative effects on the ecological environment.Especially in recent years,the haze pollution dominated by fine particulate matter(PM_2.5)has posed a threat to the healthy development of cities.The Yangtze River Delta（YRD）,the pioneer area of urbanization and economic development in China,has discharged lots of industrial pollutants and suffered serious haze pollution.Therefore,to coordinate the contradiction between urbanization and PM_2.5 pollution and to promote the transition from rapid development to high-quality development in the YRD,it is necessary to clarify the relationship between PM_2.5 concentration and urbanization.Taking the 41 cities in the YRD as the study area,the thesis starts from PM_2.5concentration estimation.Firstly,based on the merged Moderate Resolution Imaging Spectroradiometer（MODIS）aerosol optical depth（AOD）data,a two-stage model combining the linear mixed effect model（LME）and the geographically weighted regression model（GWR）was developed,which took the temporal heterogeneity and spatial heterogeneity into account and realized the accurate estimation of the historical PM_2.5 concentration.Secondly,mathematical statistics and GIS spatial analysis methods were adopted to clarify the spatio-temporal evolution characteristics of PM_2.5concentration and urbanization in the YRD from 2003 to 2018.Thirdly,taking spillover effect into account,a spatial Durbin（SDM）model was constructed to quantitatively assess the impact of urbanization on PM_2.5 concentration,and then the impact mechanism of urbanization was revealed.Fourthly,a panel vector autoregressive（PVAR）model was established to portray the two-way interactive relationship between PM_2.5 concentration and urbanization,and then the reaction mechanism of PM_2.5concentration to urbanization was explored.The main results and conclusions are as follows:（1）Based on merged MODIS AOD data,a two-stage model combining LME and GWR for daily PM_2.5 concentration estimation was established.After merging the four MODIS AOD datasets using linear regression fusion method,a two-stage model for PM_2.5 concentration estimation was established.In the first stage,a LME model was developed to reflect the temporal change of the relationships between PM_2.5 and merged AOD,meteorological conditions and vegetation.In the second stage,a GWR model was developed to reflect the spatial change of the relationships between PM_2.5 and social economic and topographical factors.The results showed that the CV R² of the two-stage model was 0.82,higher than multiple linear regression model（CV R²=0.41）and geographically weighted regression model（CV R²=0.52）,and the two-stage model can be used to estimate historical PM_2.5 concentration.（2）The spatio-temporal evolution characteristics of PM_2.5 concentration and urbanization were revealed.The results of PM_2.5 concentration time series analysis showed that only 18.83%of the YRD changed significantly at pixel scale,showing a downward trend,while at urban scale and regional scale,PM_2.5 concentration showed a trend of“up-fluctuation change-down”.From the perspective of spatial pattern evolution,PM_2.5concentration was always high in north while low in south.The gravity center of PM_2.5 concentration was located in Nanjing during the past 16 years.The population density,urbanization rate,built-up area ratio and per capita GDP showed steady increasing trends during the 16-year period.The high values of these indicators were similar in spatial distribution,mainly concentrated in Shanghai,Southern Jiangsu and Hangzhou Bay cities in Zhejiang,while the low values were quite different in spatial distribution.Compared with population density,built-up area ratio and per capita GDP,the distance between the gravity center centers of PM_2.5 concentration and urbanization rate was the shortest,indicating that they were most similar in spatial pattern.（3）The impact mechanism of urbanization on PM_2.5 concentration was revealed by constructing the spatial Durbin model.The results showed that there was a significant positive spatial spillover effect of PM_2.5 concentration among cities;the impact of population urbanization on PM_2.5 concentration was greater than that of economic urbanization,while the impact of land urbanization was not significant;the improvement of population urbanization level can not only lead to the increase of PM_2.5concentration in the local city but also in the adjacent cities.Also,the change of economic urbanization level can affect the PM_2.5 concentration of both the local city and adjacent cities.The relationship between economic urbanization and PM_2.5concentration was a significant inverted“U”curve.The impact mechanism of urbanization on PM_2.5 concentration was revealed based on the estimation results.（4）A panel vector autoregressive model was established to explore the reaction mechanism of PM_2.5 concentration on urbanization.The results showed that population urbanization and economic urbanization were the important reasons for the change of PM_2.5 concentration,and PM_2.5 concentration also had a significant reaction on economic urbanization.When the population and economic urbanization levels grew,PM_2.5 concentration increased rapidly.The response intensity of PM_2.5 concentration to population urbanization first increased and then decreased,and the response intensity of it to economic urbanization decreased in general.Regarding to the feedback effect,the increase of PM_2.5 concentration showed an inhibitory effect on the growth of population and economic urbanization,but the effect was lagging.The contribution of population and economic urbanization to the change of PM_2.5 concentration were higher than that of PM_2.5 concentration to population and economic urbanization.Based on the estimated results of panel vector autoregressive model,the reaction mechanism of PM_2.5 concentration to urbanization was revealed.There are 53 figures,34 tables and 311 references in this thesis.