Chemistry of Atmospheric Fine Particles During the COVID-19 Pandemic in a Megacity of Eastern China.

Lei Liu,Qi Yuan,Congbo Song,Chuanhua Ren,Rongguang Du,Xin Huang,Bowen Liu,Shanshan Tang,Xiaomi Teng,Liang Xu,Gongda Lu,Rui Hu,Xiaoye Zhang,Zongbo Shi,Weijun Li,Yinxiao Zhang,Jian Zhang

doi:10.1029/2020gl091611

Abstract

Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID‐19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas‐phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3 − and SO4 2− formation was observed during the COVID‐19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3 − decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID‐19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities.

Highlights

Atmospheric particulate matter (PM) exerts significant impacts on air quality, climate change, and public health (IPCC, 2013; West et al, 2016)
Based on the time nodes of notifications and responses on COVID-19 epidemic prevention and control released by Zhejiang Province (Table S2), the whole observation period is divided into four stages: pre-COVID (1–23 January), Spring Festival (24 January to 3 February), COVID lockdown (4–19 February), and post-COVID (20 February to 31 March)
The Spring Festival and COVID lockdown were covered by the COVID-19 pandemic period when similar strictest controls were imposed by local governments

Summary

Introduction

Atmospheric particulate matter (PM) exerts significant impacts on air quality, climate change, and public health (IPCC, 2013; West et al, 2016). The megacities in developing countries, such as China and India, are facing severe air pollution, especially the fine particle (PM2.5) problem because of their fast-growing economy and urbanization in past decades (Fu & Chen, 2017; Gurjar et al, 2016). The Chinese State Council implemented the “Air Pollution Prevention and Control Action Plan” in 2013 (Chinese State Council, 2013). Anthropogenic emissions of major air pollutants decreased largely (e.g., 59% for SO2, 21% for NOx, and 33% for primary PM2.5) in China during 2013–2017 Despite large reductions in primary emissions, heavy haze episodes still occur in LIU ET AL

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