Environmental Indicator for COVID-19 Non-Pharmaceutical Interventions

A novel coronavirus (COVID-19) has caused viral pneumonia worldwide, posing a major threat to international health. Our study reports that city lockdown is an effective way to reduce the number of new cases and the nitrogen dioxide (NO₂) concentration can be used as an environmental lockdown indicator to evaluate the effectiveness of lockdown measures. The airborne NO₂ concentration steeply decreased over the vast majority of COVID-19-hit areas since the lockdown. The total number of newly confirmed cases reached an inflection point about two weeks since the lockdown and could be reduced by about 50% within 30 days of the lockdown. The stricter lockdown will help newly confirmed cases to decline earlier and more rapidly, and at the same time, the reduction rate of NO₂ concentration will increase. Our research results show that NO₂ satellite observations can help decision makers effectively monitor and manage non-pharmaceutical interventions in the epidemic.