As the world went into lockdown a year ago, air pollution plummeted. But the cleaner air didn’t last. For one, in places like California, Oregon, and Washington, record-breaking wildfires meant that at least temporarily, 77 of the world’s most polluted cities were in the United States.

And despite the fact that the pandemic canceled flights and shrank traffic on roads, only around a fifth of the world’s cities ended up meeting the World Health Organization’s annual guidelines for air quality.

A new report from IQAir, a Switzerland-based air quality technology company, maps how air pollution changed around the world in 2020, using data from tens of thousands of air quality sensors in 106 countries. The pandemic initially caused a major shift; air quality improved in 84% of all the countries that were monitored. “In 2020, we were part of this unexpected scientific experiment in which we were able to determine that with a change in behavior, we can stop the vicious cycle of having really elevated levels of pollution,” says Glory Dolphin Hammes, CEO of the company’s North American branch.

MORE