Joint Occurrence of Heavy PM2.5 Pollution Episodes and Persistent Foggy Days in Central East China

Caixia Yu,Dong Liu,Yuanjian Yang

doi:10.3389/fenvs.2021.821648

Abstract

Although many severe pollution events in Central and East China have been analyzed in recent years, the heavy PM2.5 pollution episode happened on persistent foggy days from January 13 to 18, 2018 was unique, characterized by explosive increase and sharp decrease in PM2.5 (particles with kinetic equivalent diameter less than or equal to 2.5 microns) concentration. Based on hourly data of ground level meteorological parameters, PM2.5 data and CALIPSO-based (the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) aerosol data, combined with ECMWF (European Centre for Medium-Range Weather Forecasts) reanalysis data and radiosonde temperature profile, a comprehensive analysis was conducted to reveal the meteorological reasons for the evolution of the episode at horizontal and vertical scales. The PM2.5 concentration experienced four stages: a slow-increase phase, rapid-increase phase, rapid-decrease phase, and rebound phase. Results show that because Central and East China (CEC) were located at the back of a high-pressure system, humid southerly winds and near surface inversion (NSI) were responsible for the slow accumulation of pollutants. The rapid-increase phase was attributed to pollution transport at both ground level and in the lower troposphere because of weak cold air invasion. The significant subsidence at 500 hPa and 700 hPa intensified the NSI and led to dense fog. In that case, corresponding to the supersaturated atmosphere, the particles entered the fog droplets and were scavenged partly by deposition at night and were resuspended on the next day when the atmosphere was unsaturated. Our findings provide convincing evidence that surface PM2.5 rapid-decrease phase and the rebound phase were closely associated with dense fog process.

Highlights

In recent years, severe air pollution events have received media and public coverage as common phenomena in China (Guo et al, 2011; Ding and Liu, 2014; Wang et al, 2019)
In the Beijing-Tianjin-Hebei region (BTH) and Yangtze River Delta region (YRD), large amounts of data indicate that air pollution has been very serious as a consequence of the phenomenal economic growth (Zhang et al, 2012; Wang et al, 2015; Zhang et al, 2015; Zheng et al, 2018)
The heavy air pollution episode accompanied by dense fog in Central and East China (CEC) was taken as an example to comprehensively analyze the driving meteorological conditions for slow-increase, rapidincrease and short-term dissipation of PM2.5 pollution by using meteorological data; real-time pollutant concentration monitoring data; and vertical aerosol extinction coefficient data that were monitored by CALIPSO

Summary

Introduction

Severe air pollution events have received media and public coverage as common phenomena in China (Guo et al, 2011; Ding and Liu, 2014; Wang et al, 2019). The heavy air pollution episode accompanied by dense fog in CEC was taken as an example to comprehensively analyze the driving meteorological conditions for slow-increase, rapidincrease and short-term dissipation of PM2.5 pollution by using meteorological data (including high-resolution sounding data, surface observation data, and reanalysis data); real-time pollutant concentration monitoring data; and vertical aerosol extinction coefficient data that were monitored by CALIPSO.

Results

Conclusion