Air quality dramatically improved in nine major cities across the globe as people shelter in their homes to help curb the spread of the novel coronavirus, a new report finds. The report, produced by Swiss company IQAir, pulls together government data from Delhi, London, Los Angeles, Milan, Mumbai, New York City, São Paulo, Seoul, Wuhan, and Rome.

Places typically choked with worse air pollution saw the most extreme drops

Places typically choked with worse air pollution saw the most extreme drops in fine particulate matter, or soot. Delhi saw a 60 percent reduction in pollution over a three-week period while its stay-at-home order took effect, compared to the same period last year. Seoul, South Korea, saw a 54 percent decrease. Soot in Wuhan, China, dropped by 44 percent.

IQAir manufactures air purifiers and pollution monitors but also maintains online air quality maps. An interactive real-time map — a collaboration between IQAir and United Nations environmental and sustainability programs — provides information about the air quality index across major cities, along with a ranking of where air pollution is worst.

The data backs up previous observations of how the air has cleared up during the pandemic as nonessential businesses shut down and planes, trains, and cars emptied. NASA shared maps in early March depicting a dramatic drop in China of another pollutant pumped out by tailpipes that inflames airways, nitrogen dioxide. NASA similarly saw a 30 percent reduction in nitrogen dioxide emissions over the Northeast United States in March.

Rome was the only one of the 10 cities that actually saw an increase in soot over the three-week period. More people using their heating systems at home could be one culprit for poorer air quality, according to the report.

Cleaner air is a welcome reprieve during a pandemic caused by a virus that affects the lungs, but it’s not forecast to last. Air pollution is expected to rebound after restrictions set during the pandemic loosen. Similar rebounds have been observed with air quality and greenhouse gas emissions after other economic shocks like the 2008 recession.