Opposite impact of emission reduction during the COVID-19 lockdown period on the surface concentrations of PM2.5 and O3 in Wuhan, China

Hao Yin; Cheng Liu; Qihou Hu; Ting Liu; Shuntian Wang; Meng Gao; Shiqi Xu; Chengxin Zhang; Wenjing Su

doi:10.1016/j.envpol.2021.117899

Opposite impact of emission reduction during the COVID-19 lockdown period on the surface concentrations of PM_2.5 and O₃ in Wuhan, China

Environ Pollut. 2021 Nov 15:289:117899. doi: 10.1016/j.envpol.2021.117899. Epub 2021 Aug 2.

Authors

Hao Yin¹, Cheng Liu², Qihou Hu³, Ting Liu⁴, Shuntian Wang¹, Meng Gao⁵, Shiqi Xu⁴, Chengxin Zhang⁶, Wenjing Su⁴

Affiliations

¹ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei, 230031, China; Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026, China.
² Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei, 230031, China; Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China; Key Laboratory of Precision Scientific Instrumentation of Anhui Higher Education Institutes, University of Science and Technology of China, Hefei, 230026, China; Anhui Province Key Laboratory of Polar Environment and Global Change, University of Science and Technology of China, Hefei, 230026, China. Electronic address: chliu81@ustc.edu.cn.
³ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, HFIPS, Chinese Academy of Sciences, Hefei, 230031, China.
⁴ School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China.
⁵ Department of Geography, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China.
⁶ Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026, China.

Abstract

To prevent the spread of the COVID-19 epidemic, the Chinese megacity Wuhan has taken emergent lockdown measures starting on January 23, 2020. This provided a natural experiment to investigate the response of air quality to such emission reductions. Here, we decoupled the influence of meteorological and non-meteorological factors on main air pollutants using generalized additive models (GAMs), driven by data from the China National Environmental Monitoring Center (CNEMC) network. During the lockdown period (Jan. 23 - Apr. 8, 2020), PM_2.5, PM₁₀, NO₂, SO₂, and CO concentrations decreased significantly by 45 %, 49 %, 56 %, 39 %, and 18 % compared with the corresponding period in 2015-2019, with contributions by S(meteos) of 15 %, 17 %, 13 %, 10 %, and 6 %. This indicates an emission reduction of NO_x at least 43 %. However, O₃ increased by 43 % with a contribution by S(meteos) of 6 %. In spite of the reduced volatile organic compound (VOC) emissions by 30 % during the strict lockdown period (Jan. 23 - Feb. 14, 2020), which likely reduced the production of O₃, O₃ concentrations increased due to a weakening of the titration effect of NO. Our results suggest that conventional emission reduction (NO_x reduction only) measures may not be sufficient to reduce (or even lead to an increase of) surface O₃ concentrations, even if reaching the limit, and VOC-specific measures should also be taken.

Keywords: Atmospheric pollution; Generalized additive models; Meteorological factors influence; Titration effect; VOC reduction.

MeSH terms

Air Pollutants* / analysis
Air Pollution* / analysis
Air Pollution* / prevention & control
COVID-19*
China
Communicable Disease Control
Environmental Monitoring
Humans
Particulate Matter / analysis
SARS-CoV-2

Substances

Air Pollutants
Particulate Matter