Spatiotemporal Patterns Of PM_2.5 Concentration In Air Pollution Transmission Channel Of Beijing-Tianjin-Hebei From 2000 To 2015

It is of great significance for preventing and controlling regional air pollution to understand spatiotemporal patterns of PM2.5 pollution in air pollution transmission channel(also known as "2+26"cities)of the Beijing-Tianj in-Hebei area.We analyzed the temporal and spatial evolution characteristics of PM2.5 concentration of air pollution transmission channel of Beijing-Tianjin-Hebei with trend analysis and gravity center analysis,based on the PM2 5 concentration products obtained from the combination of satellite remote sensing data,model simulation and site monitoring data from 2000 to 2015.The land use change,meteorological conditions and industrial structure in the study area were analyzed,and the relationship between them and PM2.5 concentration was discussed.This study could provide reference and support for policy formulation and implementation of air pollution control measures in Beijing-Tianjin-Hebei regions.(1)From 2000 to 2015,The PM2.5 concentration was lower in the west and higher in the east with the Taihang Mountain as the demarcation.And that in the center of the city was higher than that in surrounding regions.The area where PM2 5 concentration was in 50?80 ?g/m3 was the largest,accounting for more than 37%of the total area.Shanxi Province has the best air quality,followed by Beijing and Henan Province,and Hebei provinces,Tianjin and Shandong provinces have the worse air pollution.(2)The concentration of PM2.5 generally showed an increasing trend from 2000 to 2015,especially during 2000?2007.The area with significant increasing trend during 2000?2007 accounted for 88.48%of the total area.In 2015,the monthly variation trend of PM2.5 concentration in the whole region and cities presented a "U" type as a whole.PM2 5 concentration was higher in winter and spring and lower in summer and autumn.(3)The gravity center of PM2 5 pollution was located at the junction of Hengshui,Xingtai and Dezhou.The gravity center of high concentration of PM2 5 was distributed in Baoding City,Cangzhou City,Hengshui City,Xingtai City and Dezhou City.The gravity center of low PM2 5 concentration is located in the Taihang Mountains as a whole,at the junction of Shijiazhuang City,Yangquan City and Jinzhong City.During the study period,the migration trajectory of PM2 5 concentration gravity centers have changed significantly.(4)From 2000 to 2015,PM2.5 concentration increased in all land use types.The area of construction land and water increased,while other land use/cover types decreased.Wind speed in the region showed a significant downward trend.The northwest airflow is dominant over the surface during winter,which forms the atmospheric transmission channel from northwest to southeast.In addition,PM2.5concentration was easily to increase with special topographic conditions and the economic structure dominated by the secondary industry.(5)Exposure level of PM2.5 polluted population in "2+26"cities increased gradually.Beijing,Tianjin and Baoding City had high levels of pollution exposure,more than 90%of the total population were exposed.Taiyuan City,Changzhi City,Yangquan City and Jincheng City of Shanxi Province were not polluted during the study period.The joint prevention and control of PM2.5 pollution in Beijing,Tianjin,Hebei and its surrounding areas can be carried out from three aspects:controlling pollution sources,strengthening legal supervision and optimizing industrial structure.