Lockdowns implemented in response to COVID-19 have caused an unprecedented reduction in global economic and transport activity . In this study, variation in the concentration of health-threatening air pollutants (PM2.5, NO2, and O3) pre- and post-lockdown was investigated at global, continental, and national scales . We analyzed ground-based data from> 10,000 monitoring stations in 380 cities across the globe . Global-scale results during lockdown (March to May 2020) showed that concentrations of PM2.5 and NO2 decreased by 16.1% and 45.8%, respectively, compared to the baseline period (2015–2019). However, O3 concentration increased by 5.4% . At the continental scale, concentrations of PM2.5 and NO2 substantially dropped in 2020 across all continents during lockdown compared to the baseline, with a maximum reduction of 20.4% for PM2.5 in East Asia and 42.5% for NO2 in Europe . The maximum reduction in O3 was observed in North America (7.8 %), followed by Asia (0.7 %), while small increases were found in other continents . At the national scale, PM2.5 and NO2 concentrations decreased significantly during lockdown, but O3 concentration showed varying patterns among countries . We found maximum reductions of 50.8% for PM2.5 in India and 103.5% for NO2 in Spain . The maximum reduction in O3 (22.5 %) was found in India . Improvements in air quality were temporary as pollution levels increased in cities since lockdowns were lifted . We posit that these unprecedented changes in air pollutants were mainly attributable to reductions in traffic and industrial activities . Column reductions could also be explained by meteorological variability and a decline in emissions caused by environmental policy regulations . Our results have implications for the continued implementation of strict air quality policies and emission control strategies to improve environmental and human health.