Intraseasonal variation of the northeast Asian anomalous anticyclone and its impacts on PM2.5 pollution in the North China Plain in early winter

The canonical view of the northeast Asian anomalous anticyclone (NAAA) is a crucial factor for determining poor air quality (i.e., higher particulate matter, PM2.5 concentrations) in the North China Plain (NCP) on the interannual timescale. However, there is considerable intraseasonal variability in the NAAA in early winter (November-January), and the corresponding mechanism of its impacts on PM2.5 pollution in the NCP is not well understood. Here, we find that the intraseasonal NAAA usually establishes quickly on day 3 prior to its peak day with a duration of 8 d, and its evolution is closely tied to the Rossby wave from upstream (i.e., the North Atlantic). Moreover, we find that the NAAA with a westward tilt might be mainly related to the wavenumbers 3-4. Further results reveal that against this background, the probability of regional PM2.5 pollution for at least 3 d in the NCP is as high as 69 % (80 % at least 2 d) in the Nov-Jan (NDJ) period 2000-2021. In particular, air quality in the NCP tends to deteriorate on day 2 prior to the peak day and reaches a peak on the next day with a life cycle of 4 d. In the course of PM2.5 pollution, a shallower atmospheric boundary layer and stronger surface southerly wind anomaly associated with the NAAA in the NCP appear 1 d earlier than poor air quality, which provides dynamic and thermal conditions for the accumulation of pollutants and finally occurrence of the PM2.5 pollution on the following day. Furthermore, we show that the stagnant air leading to poor air quality is determined by the special structure of temperature in the vertical direction of the NAAA, while weak ventilation conditions might be related to a rapid build-up of the NAAA. The present results quantify the impact of the NAAA on PM2.5 pollution in the NCP on the intraseasonal timescale.

Automated summary

The study investigates the impact of the northeast Asian anomalous anticyclone (NAAA) on PM2.5 pollution in the North China Plain (NCP) during early winter. Results show that the NAAA usually forms rapidly three days prior to its peak day with a duration of eight days and its evolution is associated with Rossby waves from the North Atlantic. Moreover, the NAAA with a westward tilt is found to be mainly related to wavenumbers 3-4. Additionally, the study reveals that the probability of PM2.5 pollution lasting for at least three days in the NCP during November-January (NDJ) period is as high as 69% (80% for at least two days) from 2000 to 2021.