Puzzling Haze Events in China During the Coronavirus (COVID-19) Shutdown

Yunhua Chang; Ru-Jin Huang; Xinlei Ge; Xiangpeng Huang; Jianlin Hu; Yusen Duan; Zhong Zou; Xuejun Liu; Moritz F Lehmann

doi:10.1029/2020GL088533

Puzzling Haze Events in China During the Coronavirus (COVID-19) Shutdown

Geophys Res Lett. 2020 Jun 28;47(12):e2020GL088533. doi: 10.1029/2020GL088533. Epub 2020 Jun 24.

Authors

Yunhua Chang¹, Ru-Jin Huang², Xinlei Ge³, Xiangpeng Huang³, Jianlin Hu³, Yusen Duan⁴, Zhong Zou⁵, Xuejun Liu⁶, Moritz F Lehmann⁷

Affiliations

¹ KLME & CIC-FEMD, Yale-NUIST Center on Atmospheric Environment Nanjing University of Information Science and Technology Nanjing China.
² State Key Laboratory of Loess and Quaternary Geology, Center for Excellence in Quaternary Science and Global Change, and Key Laboratory of Aerosol Chemistry and Physics Institute of Earth and Environment, Chinese Academy of Sciences Xi'an China.
³ Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering Nanjing University of Information Science and Technology Nanjing China.
⁴ Shanghai Environmental Monitoring Center Shanghai China.
⁵ Department of Environmental Science and Engineering Fudan University Shanghai China.
⁶ College of Resources and Environmental Sciences China Agricultural University Beijing China.
⁷ Department of Environmental Sciences University of Basel Basel Switzerland.

Abstract

It is a puzzle as to why more severe haze formed during the New Year Holiday in 2020 (NYH-20), when China was in an unprecedented state of shutdown to contain the coronavirus (COVID-19) outbreak, than in 2019 (NYH-19). We performed a comprehensive measurement and modeling analysis of the aerosol chemistry and physics at multiple sites in China (mainly in Shanghai) before, during, and after NYH-19 and NYH-20. Much higher secondary aerosol fraction in PM_2.5 were observed during NYH-20 (73%) than during NYH-19 (59%). During NYH-20, PM_2.5 levels correlated significantly with the oxidation ratio of nitrogen (r ² = 0.77, p < 0.01), and aged particles from northern China were found to impede atmospheric new particle formation and growth in Shanghai. A markedly enhanced efficiency of nitrate aerosol formation was observed along the transport pathways during NYH-20, despite the overall low atmospheric NO₂ levels.

Keywords: COVID‐19; emission reduction; fine particle; haze; novel coronavirus.