Spatial-temporal Evolution Characteristics And Influencing Factors Of Urban Air Quality In North China

With the rapid development of China’s economy and the acceleration of the urbanization process,the problem of air pollution is becoming more and more serious,especially in recent years,the smog weather represented by the Beijing-Tianjin-Hebei region has occurred frequently.The situation of air pollution in the Beijing-Tianjin-Hebei region is not optimistic due to the high concentration and high emission of atmospheric pollutants,coupled with unfavorable natural conditions such as topography and meteorology,and external factors such as regional pollution transmission.The Beijing-Tianjin-Hebei region is the major urban agglomeration in North China,which is a national strategy to drive the development of North China,Based on the background of reducing the harm caused by air pollution to human health and the environment and the coordinated development of air,it is particularly important to provide data basis for pollution prevention and control measures and to study the spatio-temporal evolution characteristics of air quality and air pollutants in the Beijing-Tianjin-Hebei region of North China,and analyze the influencing factors of air pollution.Based on the air quality monitoring data of 13 cities at the prefecture level and above in the Beijing-Tianjin-Hebei region from 2018 to 2020,and with the help of the air quality index evaluation system and spatial interpolation,the spatial and temporal variation characteristics of AQI and the mass concentrations of CO,NO2,O3,PM10,PM2.5 and SO2 are studied,and the influencing factors of air pollution are discussed.The main findings of the study are as follows:（1）Based on numerical statistical analysis,the air quality compliance rates in the Beijing-Tianjin-Hebei region from 2018 to 2020 were 69.87%,70.69% and 81.04%,respectively,and the overall compliance rate increased by 11.17 percentage points,and the air quality showed a good development trend;The concentrations of six major pollutants showed a downward trend,with the largest declines of CO,NO2,O3,PM10,PM2.5 and SO2 were Langfang,Beijing,Baoding,Zhangjiakou,Baoding and Tangshan,respectively,with 35.82%,25.94%,12.19%,38.78%,24.49% and 44.08%,respectively.（2）The air quality index and the six major pollutants showed obvious seasonal variation,and the seasonal variation of air quality were stepped,namely winter > spring> autumn > summer,The concentration of major pollutants（expect O3）and AQI also showed consistent seasonal variation characteristics of "summer superiority and winter inferiority".The seasonal characteristics of O3 were just the opposite,which was characterized by "winter superiority and summer inferiority".Based on spatial interpolation method,AQI and the mass concentration of six major pollutants was exhibited consistent spatial heterogeneity with " low in the north high in the south".（3）The AQI of Beijing-Tianjin-Hebei region had obvious spatial autocorrelation,the Moran Index（Moran’s I）fluctuated around 0.4,the determination coefficient of particle mass concentration was 0.75,and the correlation coefficient was 0.87,which was obviously positive correlation;the correlation coefficients between PM2.5 and CO,NO2 and SO2 ranged from 0.71 to 0.92,0.26 to 0.78,and 0.31 to 0.67,respectively,and the difference was obviously related to seasonal variation.（4）The six major pollutants in the Beijing-Tianjin-Hebei region are greatly affected by temperature and barometric pressure.The strongest correlation coefficients between temperature and CO,NO2,O3,PM10,PM2.5 and SO2 in the Beijing-Tianjin-Hebei region were-0.883,-0.828,0.888,-0.876 and-0.837,respectively.The strongest correlation coefficients of barometric pressure and CO,NO2,O3,PM10,PM2.5 and SO2 in the Beijing-Tianjin-Hebei region were 0.82,0.87,-0.94,0.82,0.79 and 0.80,respectively.Wind speed,relative humidity and precipitation and its correlation is weak.（5）The air pollution in the Beijing-Tianjin-Hebei region is mainly affected by heavy industry.According to the grey correlation model,the total amount of energy and the added value of the secondary industry rank the top two in the overall correlation degree.The trajectory and cluster analysis of the Beijing found that it was mainly affected by the Siberian air flow,the Mongolian air flow and the air flow in liaoning,Henan and Shandong Bohai sea areas.Using PSCF analysis of pollution source,the pollutants source were seriously polluted by the surrounding heavy industrial cities,mainly came from Liaoning in the northeast,Shandong in the east and Hebei and Henan in the southwest.