The increase of surface
ozone during the Corona
Virus Disease 2019 (COVID-19) lockdown in China has aroused great concern. In this study, we combine 1.5 years of measurements for
ozone,
volatile organic compounds (VOCs), and
nitrogen oxide (NOX) at four sites to investigate the effect of
COVID-19 lockdown on surface
ozone in Dongguan, an industrial city in southern China. We show that the average concentrations of NOX and VOCs decreased by 70%-77% and 54%-68% during the lockdown compared to pre-lockdown, respectively. Based on the source apportionment of VOCs, the contribution of industrial
solvent use reduced significantly (86%-94%) during the lockdown, and climbed back slowly along with the re-opening of the industry after lockdown. A slight increase in mean
ozone concentration (3%-14%) was observed during the lockdown. The rise of
ozone was the combined effect of substantial increase at night (58%-91%) and small reduction in the daytime (1%-17%). These conflicting observations in
ozone response between day and night to emission change call for a more detailed approach to diagnostic
ozone production response with precursor changes, rather than directly comparing absolute concentrations. We propose that the ratio of daily Ox (i.e. ozone + NO2) enhancement to solar radiation can provide a diagnostic parameter for
ozone production response during the lockdown period. Smaller ratio of daily OX (ozone + NO2) enhancement to solar radiation during the lockdown were observed from the long-term measurements in Dongguan, suggesting significantly weakened photochemistry during the lockdown successfully reduces local
ozone production. Our proposed approach can provide an evaluation of
ozone production response to precursor changes from restrictions of social activities during
COVID-19 epidemic and also other regional air quality abatement measures (e.g. public mega-events) around the globe.