Atmospheric Circulation Anomalies Related to the Winter PM2.5 Mass Concentration Rapid Decline Cases in Beijing

In this study, we investigate the atmospheric circulation anomalies related to the PM_2.5 mass concentration rapid decline cases in Beijing during winter when the PM_2.5 concentration is the greatest. During 2013 to 2021, 66 PM_2.5 concentration rapid decline days (RDDs) are identified by considering the 90 % thresholds of the difference of PM_2.5 mass concentration between two adjacent days. The composite evolution of PM_2.5 mass concentration for rapid decline cases features with a slow increase on the accumulation phase but a rapid decrease on RDDs. The composite evolution of atmospheric circulation anomalies in the lower-troposphere related to these PM_2.5 concentration rapid decline cases exhibits a southerly-to-northerly reverse of wind anomalies induced by the eastward shift of cyclonic/anticyclonic geopotential height anomalies from Kara Sea/East Asia to the Japan Sea/western Pacific. The mid-tropospheric circulation anomalies are characterized by an eastward propagation of the wave-train-like “+-+” pattern, corresponding to the lower-troposphere systems, which together promote the southerly-to-northerly reverse process. Meteorological factors in the planetary boundary layer including temperature, humidity and boundary layer height also show anomalous warm-to-cold, wet-to-dry and low-to-high reverse around RDDs, respectively. The results imply that the atmospheric circulation patterns above could be a precursor to the PM_2.5 mass concentration rapid decline cases in Beijing.