Diverse response of surface ozone to COVID-19 lockdown in China

TL;DR

This study analyzes how surface ozone levels in China responded differently across regions during COVID-19 lockdown, influenced by meteorology and emission changes of NOx and VOCs, revealing complex regional dependencies.

Contribution

It provides a comprehensive analysis of surface ozone variability across China during COVID-19 lockdown, highlighting the combined effects of meteorology and emission reductions on ozone levels.

Findings

Daytime O₃ decreased in the subtropical south but increased in other regions.

Meteorological factors had a larger impact than emission reductions in central China.

Emission reductions of NOₓ and VOCs had region-specific effects on ozone levels.

Abstract

Ozone (O$_{3}$) is a key oxidant and pollutant in the lower atmosphere. Significant increases in surface O$_{3}$ have been reported in many cities during the COVID-19 lockdown. Here we conduct comprehensive observation and modeling analyses of surface O$_{3}$ across China for periods before and during the lockdown. We find that daytime O$_{3}$ decreased in the subtropical south, in contrast to increases in most other regions. Meteorological changes and emission reductions both contributed to the O$_{3}$ changes, with a larger impact from the former especially in central China. The plunge in nitrogen oxide (NO$_{x}$) emission contributed to O$_{3}$ increases in populated regions, whereas the reduction in volatile organic compounds (VOC) contributed to O$_{3}$ decreases across the country. Due to a decreasing level of NO$_{x}$ saturation from north to south, the emission reduction in NO$_{x}$ (46%) and VOC (32%) contributed to net O$_{3}$ increases in north China; the opposite effects of NO$_{x}$ decrease (49%) and VOC decrease (24%) balanced out in central China, whereas the comparable decreases (45-55%) in these two precursors contributed to net O$_{3}$ declines in south China. Our study highlights the complex dependence of O$_{3}$ on its precursors and the importance of meteorology in the short-term O$_{3}$ variability.