As streets have emptied of traffic during the coronavirus crisis and airlines have cut flights, the changes have temporarily helped another public health crisis—air pollution. In the Northeastern U.S., nitrogen dioxide pollution (the air pollution caused by internal combustion engines burning fossil fuels) fell 30% in March as lockdowns began. Los Angeles’s usual smog has nearly disappeared . The same pattern happened earlier in China and Italy as mobility slowed, factories shut down, and hazy skies cleared.

Maps from Descartes Labs, a data analytics company, use satellite data to track the steep changes in air quality. In March and the first week of April, NO2 pollution fell around 19% in Seattle compared to the same period last year. In New York, it fell 22%; in Denver, 15%. In Los Angeles, NO2 pollution dropped 33%. As the virus spreads around other parts of the world, some cities are seeing even steeper declines. In India, where 1.3 billion people are now under lockdown, the capital of New Delhi has seen 70% drops in both nitrogen dioxide pollution and PM 2.5, tiny particles of soot. Darker blue on the maps indicates more air pollution.

There’s a direct link between air pollution and the new coronavirus, since polluted air makes people more likely to have illnesses such as asthma and lung disease that make them at greater risk of dying from COVID-19. One recent study from researchers at Harvard’s T.H. Chan School of Public Health suggests that areas that are even slightly more polluted than other areas will have more COVID-19 deaths. Air pollution is also linked to widespread deaths even without the coronavirus: The WHO estimates that around 7 million people die each year, globally, because of exposure to pollution.

The current declines in pollution are temporary; in China, as factories have reopened and people have gone back to work, skies are becoming more polluted again. The same thing will happen in the United States. But the clearer skies are also a reminder of what’s possible.

“It is not surprising that air pollution has been reduced now, because we know why we have bad air normally—we just don’t have the political will to change it,” says Gretchen Goldman, a research director at the Union of Concerned Scientists. “We already have all the tools we need that would allow us to have cleaner air all the time, irrespective of the pandemic and social distancing. We could be switching from coal to renewables. We could be adapting national standards for clean energy. We could get off fossil fuel subsidies. We could be electrifying more vehicles and allowing states to go further with their vehicles standards. We know what the solutions are.”

There’s a chance, Goldman says, that the current respite from pollution might lead to more support for change. “When people see the world that could be, it is harder to take it away,” she says. “When people see how much easier it is to breathe outside, when you see that possibility, I think it will make it harder for decision-makers to avoid taking steps to make this norm, not the exception.”