Changes in contents of PM2.5 components over Jinan city before and after implementation of epidemic control measures during the 2020 Spring Festival

ABSTRACT

To understand the influence of coronavirus disease control policies on changes in characteristics of particulate matter smaller than 2.5 μm (PM2.5), concentrations of various PM2.5 components in Jinan city before and after implementation of the epidemic control measures during the 2020 Spring Festival were studied using online monitoring data. Standardized multiple linear regression was used to analyze the contribution of meteorological factors to the variations in concentrations of PM2.5 components. After the epidemic control measures were implemented, the concentrations of PM2.5 components in the area decreased significantly, and the rate at which the daily average concentration was exceeded decreased by 24.8%. The concentrations of all PM2.5 components decreased to various degrees, with those of trace elements (TE), elemental carbon (EC), and nitrate (NO3−) having decreased significantly by 50.3%, 46.8%, and 31.5%, respectively. In terms of component proportions, those of TE and EC decreased after the epidemic control measures were initiated whereas those of ammonium (NH4+), organic matter (OM), sulfate (SO4 2− ), and mineral dust increased;the proportion of NO3 − changed slightly, and the total proportion of secondary ions SO4 2−, NO3−, and NH4 + increased by 14.3%. Comparison of the proportions of PM2.5 components showed that after the epidemic control measures were implemented, the proportions of NO3 − and EC in PM2.5 that cause a light pollution level decreased whereas those of OM, SO4 2−, and NH4 + increased. This indicated that people traveled less, motor vehicle emissions decreased, work at construction sites stopped, and NO3 − proportion was greatly reduced while epidemic control measures were in place. However, afterward, decrease in concentrations of PM2.5 components and increase in secondary transformation of volatile organic compounds led to an increase in OM concentration. Compared with those before the epidemic control measures were implemented, the NO2/SO2 and NO3– /SO4 2− ratios fell significantly, and their average values decreased by 30.0% and 14.0%, respectively, indicating that the contribution of mobile sources (e.g., automobile exhaust) to pollution had decreased during the epidemic control period. Under the influence of the control measures, the OC concentration also decreased for excellent, good, and mild pollution levels;however, the secondary organic carbon concentration increased, indicating that secondary conversions did not decrease under the epidemic control conditions. Standardized multiple linear regression analyses of meteorological factors showed that changes in the height of the boundary layer contributed the most (46.5%) to changes in concentrations of PM2.5 components before the epidemic control measures were implemented;afterward, humidity was the primary factor governing the increase in these concentrations. © 2022, The Science Press. All rights reserved.