Impact of COVID-19 lockdown on ambient levels and sources of volatile organic compounds (VOCs) in Nanjing, China

Ming Wang; Sihua Lu; Min Shao; Limin Zeng; Jun Zheng; Fangjian Xie; Haotian Lin; Kun Hu; Xingdong Lu

doi:10.1016/j.scitotenv.2020.143823

Impact of COVID-19 lockdown on ambient levels and sources of volatile organic compounds (VOCs) in Nanjing, China

Sci Total Environ. 2021 Feb 25:757:143823. doi: 10.1016/j.scitotenv.2020.143823. Epub 2020 Nov 20.

Authors

Ming Wang¹, Sihua Lu², Min Shao³, Limin Zeng², Jun Zheng¹, Fangjian Xie⁴, Haotian Lin¹, Kun Hu¹, Xingdong Lu¹

Affiliations

¹ Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China.
² College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
³ Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China. Electronic address: mshao@pku.edu.cn.
⁴ Nanjing Municipal Academy of Ecological and Environment Protection Science, Nanjing 210093, China.

Abstract

A lot of restrictive measures were implemented in China during January-February 2020 to control rapid spread of COVID-19. Many studies reported impact of COVID-19 lockdown on air quality, but little research focused on ambient volatile organic compounds (VOCs) till now, which play important roles in production of ozone and secondary organic aerosol. In this study, impact of COVID-19 lockdown on VOCs mixing ratios and sources were assessed based on online measurements of VOCs in Nanjing during December 20, 2019-Feburary 15, 2020 (P1-P2) and April 15-May 13, 2020 (P3). Average VOCs levels during COVID-19 lockdown period (P2) was 26.9 ppb, about half of value for pre-lockdown period (P1). Chemical composition of VOCs also showed significant changes. Aromatics contribution during decreased from 13% during P1 to 9% during P2, whereas alkanes contribution increased from 64% to 68%. Positive matrix factorization (PMF) was then applied for non-methane hydrocarbons (NMHCs) sources apportionment. Five sources were identified, including a source related to transport and background air masses, three sources related to petrochemical industry or chemical industry (petrochemical industry#1-propene/ethene, petrochemical industry#2-C7-C9 aromatics, and chemical industry-benzene), and a source attributed to gasoline evaporation and vehicular emission. During P2, NMHCs levels from petrochemical industry#2-C7-C9 aromatics showed the largest relative decline of 94%, followed by petrochemical industry#1-propene/ethene (67%), and gasoline evaporation and vehicular emission (67%). Furthermore, ratios of OH reactivity of NMHCs versus NO₂ level (R_OH,NMHCs/NO₂) and total oxidant production rate (P (O_X)) were calculated to assess potential influences of COVID-19 lockdown on O₃ formation.

Keywords: COVID-19; Industrial emission; Nanjing; Ozone; Source apportionment; VOCs.

MeSH terms

Air Pollutants* / analysis
COVID-19*
China
Communicable Disease Control
Environmental Monitoring
Humans
Ozone* / analysis
SARS-CoV-2
Volatile Organic Compounds* / analysis

Substances

Air Pollutants
Volatile Organic Compounds
Ozone