Zongbo Shi, University of Birmingham and William Bloss, University of Birmingham

The pandemic caused governments around the world to introduce lockdowns in early 2020, temporarily closing workplaces and emptying roads and public spaces. As economic activity slowed, so did emissions of air pollutants. Almost a year later, the effect that all this had on the air we breathe is becoming clear.

The most straightforward way to determine the effects of lockdown on air quality is to compare measurements before and after the date that the lockdown began. Earlier studies used this approach and reported big reductions in some pollutants, such as nitrogen dioxide (NO?). One study claimed that NO? emissions fell by up to 90% in Wuhan (the Chinese city where COVID-19 is believed to have emerged) at the…