Characteristics of the factors influencing transportation and accumulation processes during a persistent pollution event in the middle reaches of the Yangtze River, China

Abstract

Extreme pollution event is a major environmental concern in the middle reaches of the Yangtze River, which located at the position of a transportation hub connecting the four major air pollution areas in China. In this study, we focused on a continuous heavy air pollution event that affected Hubei from 12 to 24 January 2018, and examined the meteorological conditions, regional transport features, boundary-layer characteristics, and the evolution of PM and gaseous pollutants in Xiangyang (XY), Jingmen (JM), Jingzhou (JZ), Yichang (YC), Xiaogan (XG), and Wuhan (WH). The results showed that this pollution event was the result of joint action of fog, haze, and fog-haze transformation weather. The pure haze was mainly concentrated at the pollution-transport channel (XY and JM) of Hubei. The explosive growth of PM concentrations was more obvious in XY, JM, and JZ than that in YC, XG, and WH, with the growth and reduction rates of PM2.5 at XY station, at 20.11 and 19.50 μg/(m3·h), respectively. During the explosive growth period, northerly winds were dominant at XY, JM, JZ, XG, and WH stations, with large and weak wind speed (WS) resulted in significantly increased PM2.5 concentrations in XY and JM (transport), and in JM, JZ, and YC (accumulation), respectively. The height of northward airflow reached 2000 m in the main pollutant transport channel of Hubei. The upper and lower inversion layers would be enhanced before the explosive growth of PM concentration significantly, then be weakened by continuous transport of the northerly airflow. The concentrations of SO2, NO2, and CO decreased with the increase in WS during the explosive growth period, and O3 concentration reached maximum value at a WS of 3.5–5 m/s. The correlation analysis indicated significant differences in the effects of transport and accumulation.