Analysis on the causes of PM2.5 pollution in Nanning City in February 2020

ABSTRACT

During the novel coronavirus (COVID-19) lock down from 31st January to 2nd February, a regional atmospheric PM2.5 pollution episode had arosed concerns of society in Guangxi. Based on Nanning as an sampling site, Monitor for Aerosols and Gases in Ambient Air (MARGA), particulate LiDAR, surface meteorological and environmental data, satellite remote sensing data and modeled HYSPLIT4 trajectory were used to analyze the cause of PM2.5 pollution. According to the air quality sub-index, the observation durations were classified as the superior period, the fine period and the polluted period. The results indicated that K+ and Cl- concentrations closely related to biomass burning (BB) increased significantly during the polluted period. The average concentrations of K+ and Cl- in polluted period were 3.6 and 17.0 times higher than those corresponding figures of the superior period. The total concentration of eight water-soluble ions accounted for about 30% of PM2.5 in all three periods. The total concentration of three secondary water-soluble ions accounted for 83.33%~89.18% of the total concentration of eight ions. The high proportion of secondary inorganic components was related to the secondary transformation promoted by BB. The variation trends of proportion and levels of secondary water-soluble ions were not consistent, which was not only attributed to the emission characteristics of straw combustion, but also related to the formation mechanism and main influencing factors of different secondary inorganic ions. Straw burning spots were centralized around Nanning city during the fine period. The accumulation of direct emissions of particulate and gaseous pollutants caused by open burning of straw during the fine period under decreased boundary layer height, increased humidity and low wind speed were the main causes for atmospheric PM2.5 pollution in Nanning. During the polluted period, there was no obvious vertical transmission process of particulate matter in Nanning. The near ground was mainly affected by the southward airflow from the Beibu Gulf of Guangxi and Guangdong coastal, which indicated the regional pollution transmissions were insignificant. © 2021, Science Press. All right reserved.