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Responding to the 2020 COVID-19 outbreak, China imposed an unprecedented lockdown producing reductions in air pollutant emissions. However, the lockdown driven air pollution changes have not been fully quantified. We applied machine learning to quantify the effects of meteorology on surface air quality data in 31 major Chinese cities. The meteorologically normalized NO2, O3, and PM2.5 concentrations changed by -29.5%, +31.2%, and -7.0%, respectively, after the lockdown began. However, part of this effect was also associated with emission changes due to the Chinese Spring Festival, which led to ~14.1% decrease in NO2, ~6.6% increase in O3 and a mixed effect on PM2.5 in the studied cities that largely resulted from festival associated fireworks. After decoupling the weather and Spring Festival effects, changes in air quality attributable to the lockdown were much smaller: -15.4%, +24.6%, and -9.7% for NO2, O3, and PM2.5, respectively. Plain Language Summary Strict lockdown measures imposed in most countries to stop the 2020 COVID-19 pandemic spread, led to changes in air pollutant concentrations. The lockdown in China started at the start of the Chinese Spring Festival (CSF), making it difficult to disentangling the lockdown from the CSF effects. We applied a machine learning meteorological normalization technique that considered the effects of lunar holidays that fall on different Gregorian dates in different years and accounted for meteorological effects on surface air quality. We found that the normal CSF in 2015-2019 led to reproducible changes in NO2 (-14.1%) and O3 (+6.6%) concentrations, and a mixed effect on PM2.5 across China. After decoupling the CSF effects, the 2020 lockdown produced limited changes in air quality. Thus, measures similar to the COVID-19 lockdown will suffice to reduce NO2 levels in China to be below WHO guidelines but unlikely to attain the WHO PM2.5 guidelines. This methodology permits estimation of traditional holiday- and event-driven air quality changes, especially when there are recurring cultural events based on non-Gregorian dates that may overlap with intervention. [ABSTRACT FROM AUTHOR]