The two-way feedback mechanism between unfavorable meteorological conditions and cumulative aerosol pollution in various haze regions of China

Abstract. Accompanied by unfavorable meteorological conditions with stable stratification in various haze regions of China, persistent heavy aerosol pollution episodes (HPEs) lasting more than 3 consecutive days frequently occur, particularly in winter. In the North China Plain (NCP), explosive growth of fine particulate matter smaller than 2.5  µ m in diameter (PM 2.5 ), which occurs during some HPE S , is dominated by a two-way feedback mechanism between more unfavorable meteorological conditions and cumulative aerosol pollution. However, the existence of a two-way feedback mechanism such as this in other key haze regions in China is uncertain; these regions include the Guanzhong Plain (GZP), the Yangtze River Delta (YRD) region, the Two Lakes Basin (TLB; a large outflow basin connected to Hubei Province and Hunan Province), the Pearl River Delta (PRD) region, the Sichuan Basin (SB), and the Northeast China Plain (NeCP). In this study, using surface PM 2.5 and radiation observations, radiosonde observations, and reanalysis data, we observed the existence of a two-way feedback mechanism in the six abovementioned regions. In the SB, this two-way feedback mechanism is weak due to the suppression of cloudy mid-upper layers. In the more polluted NCP, the GZP, and the NeCP, the feedback is more striking than that in the YRD, the TLB, and the PRD. In these regions, the feedback of worsened meteorological conditions on PM 2.5 explains 60 %–70 % of the increase in PM 2.5 during the cumulative stages (CSs). For each region, the low-level cooling bias becomes increasingly substantial with increasing aerosol pollution and a closer distance to the ground surface. With PM 2.5 mass concentrations greater than 400  µ g m −3 , the near-ground bias exceeded −4 ∘ C in Beijing and reached up to approximately −4 ∘ C in Xi'an; this result was caused by accumulated aerosol mass to some extent. In addition to the increase in PM 2.5 caused by the two-way feedback, these regions also suffer from the regional transport of pollutants, including inter-regional transport in the GZP, trans-regional transport from the NCP to the YRD and the TLB, and southwesterly transport in the NeCP.