Impact of quarantine measures on chemical compositions of PM2.5 during the COVID-19 epidemic in Shanghai, China

Hui Chen,Juntao Huo,Qingyan Fu,Yusen Duan,Hang Xiao,Jianmin Chen

doi:10.1016/j.scitotenv.2020.140758

Abstract

The COVID-19 epidemic broke out in Wuhan, Hubei in December 2019 and in January 2020 and was later transmitted to the entire country. Quarantine measures during Chinese New Year effectively alleviated the spread of the epidemic, but they simultaneously resulted in a decline in anthropogenic emissions from industry, transportation, and import and export of goods. Herein, we present the major chemical composition of non-refractory PM2.5 (NR-PM2.5) and the concentrations of gaseous pollutants in an urban site in Shanghai before and during the quarantine period of the COVID-19 epidemic, which was Jan. 8―23 and Jan. 24―Feb. 8, respectively. The observed results show that the reduction in PM2.5 can be mainly attributed to decreasing concentrations of nitrate and primary aerosols. Nitrate accounted for 37% of NR-PM2.5 before the quarantine period when there was no emission reduction. During the quarantine period, the nitrate concentration decreased by approximately 60%, which is attributed to a reduction in the NOx concentration. Ammonium, as the main balancing cation, showed an approximately 45% simultaneous decrease in concentration. The concentrations of chloride and hydrocarbon-like organic aerosols from primary emissions also declined due to limited human activities. By contrast, sulphate and oxygenated organic aerosols showed a slight decrease in concentration, with their contributions increasing to 27% and 18%, respectively, during the quarantine period, which resulted in two pollution episodes with PM2.5 exceeding 100 μg/m3. This study provides a better understanding of the impact of quarantine measures on variations of the PM2.5 concentration and chemical compositions. Atmospheric oxidation capacities based on the oxidant (Ox = O3 + NO2) and oxidation ratios have been discussed for elucidating the source and formation of haze in an environment with lower anthropogenic emissions. With increasing contribution of secondary aerosols, lower NOx and nitrate concentrations did not completely avoid haze in Shanghai during the epidemic.

Highlights

In December 2019 and in January 2020, a cluster of COVID-19 cases was reported in Wuhan, Hubei, China (Li et al, 2020)
We investigate variations in the PM2.5 chemical composition before, during and after the CNY holiday, which can help to elucidate the impact of quarantine measures on air quality
The PM2.5 concentration decreased by 33% and 44% during Phase 2 (P2) and Phase 3 (P3), respectively

Summary

Introduction

In December 2019 and in January 2020, a cluster of COVID-19 cases was reported in Wuhan, Hubei, China (Li et al, 2020). To slow down the spread of COVID19, the Chinese government issued strict quarantine measures (lockdown) in Wuhan on Jan. 23, 2020 and enacted corresponding restrictive measures in different regions according to the level of the epidemic. These measures included reducing public transportation and closing schools and business centers. These quarantine measures effectively alleviated the spread of the COVID-19 epidemic in China (Zhang et al, 2020a) and greatly suppressed anthropogenic emissions (Wang et al, 2020a; Zhang et al, 2020b). Emission reduction did not prevent the occurrence of severe haze in China, and a plausible explanation for this is derived from a model study that showed a large emission reduction in transportation and a slight reduction in industrial production are insufficient to prevent haze in China in the winter (Wang et al, 2020a)

Methods

Results

Conclusion