[Analysis of a Pollution Process in the Beijing-Tianjin-Hebei Region Based on Satellite and Surface Observations]

The air pollution control of the Beijing-Tianjin-Hebei region (BTH region) is gradually moving toward regional joint mode. Remote sensing technology can be used to realize real-time dynamic monitoring over a wide range of space and ground-based monitoring can obtain accurate point information. Combining satellite with ground-based data, the formation and dissipation of pollution can be traced in three dimensions. For this paper, we analyzed the formation process, transmission path, coverage area, and the meteorological characteristics of the pollution process over the BTH region during March 8-10, 2018, using satellite remote sensing data, surface PM_2.5 concentration data, meteorological data, and lidar data. The results showed that an area of 200000 km² was affected by this pollution process and that the grade of the pollution reached the fourth level (moderate pollution level). The regional transmission process was very typical in this process. During 8-9 March, the occurrence frequency of the southward wind was about 50% in the Beijing-Baoding region and 100% over the southern part of Hebei. With the help of continuous southward wind, the air quality of the Beijing-Baoding area rises from the first level to the fourth level. The high value area of aerosol optical thickness moved from the western part of the Handan-Xingtai region to the front of Yanshan Mountain. On 10 March, the weak north wind affected the region and the humidity increased obviously. A pollution convergence formed in the southern part of the BTH region. The center of pollution moved southward to the east part of the Handan-Xingtai Region. In the afternoon, with the help of the eastern wind, the air quality of Beijing got better from East to West. The vertical lidar observation results showed the pollution layer above Beijing was mainly below 1000 m. There were two inversion layers below 800 m and 1200-1500 m, respectively. The inversion temperature was as high as 4-7℃, which is unfavorable for vertical diffusion of pollutants. Thus, under the high intensity of regional energy consumption and pollution emissions background, the regional heavy pollution form easily once the weather conditions are bad.