Meteorological factors related to winter severe PM2.5 pollution in China: In perspective of thresholds and relation of occurrence frequency with East Asian trough

Abstract

Meteorological factors have profound effects on the severe PM2.5 pollution in winter. The thresholds of wind speed, humidity, rainfall, and snowfall related to it are individually identified in six regions of China by combining meteorological stations' and air quality stations' data. Five mm is the daily threshold for precipitation, not only for rainfall but also for snowfall because more than 80% of severe PM2.5 pollution cases occurred below this magnitude. However, in the no-precipitation condition the thresholds comprising wind speed and relative humidity varied in regions, indicating wind speed of 2 m s−1 and relative humidity of 60% not quite practical in China. Furthermore, in this condition the frequency of adverse meteorological conditions associating with thresholds of wind speed and relative humidity evolved increasingly with 3–5 percentage points per decade and periodically with 7–16.7 years after taking 11-year moving average in the Fenhe River and Weihe River Plain (FWP), the Northeast China Plain (NEC) and the North China Plain (NCP) from 1960 to 2019. Whereas in the Sichuan Basin similar frequency peaked in the 1990s then decreased till the 2010s. In the NCP, FWP, and the Changjiang River Plain, such frequencies’ variation could be attributed to the East Asian Trough whose intensity is defined as the geopotential height gradient at 500 hPa. In addition, East Asian Trough is periodic with 7.7–20 years after taking 11-year moving average. It would be helpful in planning air quality improvements if these results are taken into consideration.