Changes in air pollution due to COVID-19 lockdowns in 2020: Limited effect on NO, PM, and PM annual means compared to the new WHO Air Quality Guidelines.

Background: Lockdowns have been fundamental to decreasing disease transmission during the COVID-19 pandemic even after vaccines were available. We aimed to evaluate and compare changes in air quality during the first year of the pandemic in different cities around the world, investigate how these changes correlate with changes in mobility, and analyse how lockdowns affected air pollutants' annual means.

Methods: We compared the concentrations of NO, PM, and PM in 42 cities around the world in the first months of the pandemic in 2020 to data from 2016-2019 and correlated them with changes in mobility using Human Development Indexes (HDIs).