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

Junting Zhong,Zhouqing Xie,Yubin Li,Xiaoye Zhang,Tianliang Zhao,Zhiqiu Gao,Linlin Wang,Xiaojing Shen,Tijian Wang,Hengde Zhang,Jizhi Wang,Shaojia Fan,Cheng Liu,Junying Sun,Hongsheng Zhang,Yaqiang Wang

doi:10.5194/acp-19-3287-2019

Abstract

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 µm in diameter (PM2.5), which occurs during some HPES, 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 PM2.5 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 PM2.5 explains 60 %–70 % of the increase in PM2.5 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 PM2.5 mass concentrations greater than 400 µg 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 PM2.5 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.

Highlights

In China, 94 % of the total population is distributed in eastern China (Yang et al, 2016), in which aerosol pollution has drawn wide attention
By comparing the mean PM2.5 mass concentration from 1 December 2016 with that of 10 January 2017 in the five regions that experienced declines in visibility (Fig. 3), we found that the heaviest aerosol pollution occurred in the North China Plain, and it was followed by the Guanzhong Plain
We found that the southern area of the North China Plain experienced a substantial reduction in its PM2.5 mass concentration, whereas an increase occurred in the middle and lower reaches of the Yangtze River, including the Two Lakes Basin and the Yangtze River Delta region; these results indicate the process of regional pollutant transport from northern China to eastern China under strong northwesterly winds

Summary

Introduction

In China, 94 % of the total population is distributed in eastern China (Yang et al, 2016), in which aerosol pollution has drawn wide attention. In the basins and plains in eastern China, aerosol pollution episodes frequently occur in winter, and these episodes cause economic loss and have adverse effects on human health (Bai et al, 2007; Matus et al, 2012; Chen et al, 2013). During the wintertime (i.e., December, January, and February) from 2013 to 2017, more than 28 persistent heavy aerosol pollution episodes (HPEs) that lasted for more than 3 consecutive days occurred in Beijing; the peak value of particulate matter smaller than 2.5 μm in diameter (PM2.5) ranged from ∼ 200 to ∼ 800 μg m−3, with a mean duration longer than 5 days (Zhong et al, 2018a, 2019). Aerosol pollution forms and further accumulates (Zhang et al, 2013; Zhong et al, 2017)

Methods

Results

Conclusion