北方55城遭沙尘侵袭！今日郑州将迎轻中度污染

Group 1 - The core viewpoint of the articles highlights the occurrence of sandstorm weather in northern China, significantly affecting air quality and leading to short-term heavy pollution in over 50 cities [1][4][6] Group 2 - The current air quality situation indicates that from February 20, sandstorm weather has affected most of the northwest and north China, with the dust moving east and south [2][4] - The cause of the sandstorm is attributed to a significant decrease in precipitation in the source areas, with rainfall in southern Mongolia and the China-Mongolia border being over 50% below the historical average [3] - As of February 21, PM10 concentrations in 55 cities reached short-term heavy or severe pollution levels, with peak PM10 levels exceeding 3000 micrograms per cubic meter in some areas [4] Group 3 - The cold air mass contributing to the sandstorm is notably strong, with wind speeds exceeding level 8 in northern regions, and localized areas experiencing winds of level 11 to 12 [6] Group 4 - Future air quality trends suggest that the main body of the sandstorm will continue to move east and south, affecting central and eastern China until the night of February 22, with potential short-term heavy pollution in various regions [7] - In Zhengzhou, air quality is expected to be good or lightly polluted on February 21, transitioning to light or moderate pollution on February 22, primarily due to PM10 [7]