The seesaw impacts between reduced emissions and enhanced AOC on O$_3$ during the COVID-19

TL;DR

The study examines how COVID-19 lockdown-induced emission reductions affected ozone levels in China, revealing a shift in formation regimes and highlighting the role of atmospheric oxidant capacity in ozone pollution.

Contribution

It provides a comprehensive analysis of ozone variations during COVID-19 using satellite, ground, and modeling data, emphasizing the importance of AOC in ozone pollution control.

Findings

Ozone formation regime shifted from VOC-limited to NOx-limited during lockdown.

Significant ozone increases in North China Plain and Yangtze River Delta linked to enhanced AOC.

Future policies should consider both ozone formation regimes and AOC effects.

Abstract

Due to the lockdown measures during the 2019 novel coronavirus (COVID-19) pandemic, the economic activities and the associated emissions have significantly declined. This reduction in emissions has created a natural experiment to assess the impact of the emitted precursor control policy on ozone (O$_3$) pollution, which has become a public concern in China during the last decade. In this study, we utilized comprehensive satellite, ground-level observations, and source-oriented chemical transport modeling to investigate the O$_3$ variations during the COVID-19 in China. Here we found that the O$_3$ formation regime shifted from a VOC-limited regime to a NOx-limited regime due to the lower NOx during the COVID-19 lockdown. However, instead of these changes of the O$_3$ formation region, the significant elevated O$_3$ in the North China Plain (40%) and Yangtze River Delta (35%) were mainly attributed to the enhanced atmospheric oxidant capacity (AOC) in these regions, which was different from previous studies. We suggest that future O$_3$ control policies should comprehensively consider the synergistic effects of O$_3$ formation regime and AOC on the O$_3$ elevation.