| Summary: | Persistent pollution often occurs in North China in winter. The study of the sub-seasonal evolution characteristics of fine particles (PM<sub>2.5</sub>) can provide a theoretical basis for the prediction and prevention of persistent pollution. Based on the high-resolution gridded data of PM<sub>2.5</sub> and NCEP/NCAR reanalysis, the sub-seasonal variation in PM<sub>2.5</sub> in North China in winter and its dominant circulation patterns from 1960/61 to 2019/20 were analyzed. The results show that, in winter, PM<sub>2.5</sub> in North China shows a dominant period of 10–20 days, and persistent heavy pollution occurs at the active phase of oscillation. Based on the PM<sub>2.5</sub> quasi-biweekly oscillation (QBWO) events, the 850 hPa wave train can be classified into four categories. It was found that, during the active phase of PM<sub>2.5</sub> QBWO, the wind speed is weak and humidity is high in the low-troposphere for all of the four event types, while the quasi-biweekly 850 hPa wave train and the track of geopotential height anomaly are significantly different. Based on the characteristics of circulation evolution, these four types of events can be named as eastward, split southward, southeastward, and merged event. The energy conversion between the basic flow and the quasi-biweekly disturbance, and the mean flow difference are responsible for the circulation diversity for different PM<sub>2.5</sub> QBWO events. The above research results can provide a theoretical basis for pollutant prediction.
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