[Analysis of Typical Weather Circulation Patterns of Heavy PM Pollution and the Transport Pattern in the Yangtze River Middle Basin].

The dominant transportation and accumulation patterns of heavy PM pollution events over the Yangtze River middle basin were identified based on the obliquely rotated T-mode principal component analysis (PCT) method and the daily mean surface pressure. The heavy PM pollution events over the Yangtze River middle basin during 2015-2019 were divided into four patterns, namely, PCT1:high-pressure bottom transport pattern (number of days:41 d, accounting for 55.4% of the total heavy PM pollution days), PCT2:low-pressure convergence accumulation pattern (12 d, 16.

[Characteristics of Atmospheric Particulate Matter Pollution and the Unique Wind and Underlying Surface Impact in the Twain-Hu Basin in Winter].

To understand the recent characteristics of atmospheric environmental changes in the Twain-Hu(Hunan-Hubei) Basin, including the middle reaches of the Yangtze River, this paper uses near-surface PM and PM observational data for the Twain-Hu Basin in the winters of 2015 to 2019, combined with wind-speed, topography, the normalized difference vegetation index(NDVI), and other datasets. The results show that:① PM pollution occurred frequently in the winters of 2015-2019 in the Twain-Hu Basin, and Xiangyang and Jingmen in the western part of the basin, experience PM pollution on an average of 62 and 61 days in winter(PM>75 μg·m). And the heavy pollution days in Xiangyang reached 19 more days(PM>150 μg·m), indicating that the Twain-Hu Basin is an air pollution center in the middle reaches of the Yangtze River Basin; ② Spatially, pollution in the Twain-Hu Basin is heavier in the northwest than in the southeast, and in the urban agglomeration, which is mainly related to the regional transport of air pollutants by the winter monsoon and the high levels of emissions from urban areas; ③ A "U-shaped" nonlinear relationship was observed between near-surface wind speeds and PM and PM concentrations.