On March 2, European Society of Cardiology researchers published a study on how dirty air shortens more lives than wars, smoking, parasitic disease and HIV. They said they’re findings suggest that the world faces an air pollution “pandemic.”

Barely two weeks have passed and we’re in the midst of a very different pandemic.

Although pollution still poses an existential threat for millions of people each year, the pandemic we’re reckoning with on a global scale through unprecedented isolation measures has had a measurable effect on air quality in some places.

Satellite imagery of three coronavirus hotspots shows a dramatic decline in air pollution in just the past couple weeks as China, Iran and Italy brought their economies to an abrupt halt. One Stanford University scientist estimated that China’s sweeping lockdown has saved 77,000 lives—about seven times the COVID-19 death rate so far—by curbing emissions from cars and factories.

Amid a statewide stay-at-home mandate to curb the spread of the novel coronavirus, the Bay Area has seen vehicle traffic plummet. Rush hour to and from S.F. is moving 22 percent faster, by some metrics. The air really does feel much cleaner.

But how much these blue skies and crisp air owe to our regional lockdown remains to be seen, according to Kristine Roselius, a spokeswoman for the Bay Area Air Quality Management District (BAAQMD).

“We’ve gotten this question a lot from other reporters and members of the public,” she said. “And the answer right now, at least, is that it’s really hard to tell.”

Rain, winds and unsettled weather of the sort we’ve had lately has improved the air quality lately, so it’s hard to say how much of this owes to the reduction in traffic and urban emissions. The district would need months of data and draw comparisons to prior years to come up with a reliable comparison.

“Now that said, if you take out the largest sources of pollution in the Bay Area—and that would be cars—then there will be reduced pollution levels,” Roselius said. “We did do a back-of-the-envelope calculation and we have some reduction in numbers, but it’s hard to say by exactly how much.”

The other factor in play is that the district would be measuring different types of pollution. That is, fine particulates produced by cars known as PM2.5, carbon dioxide greenhouse gas emissions and nitrogen oxide, which creates smog.

“Let’s say there’s a reduction in traffic by 70 percent,” she said. “Then, we would see a likely drop in pollution—and these are estimates—of 20 percent for PM2.5, about a 38 percent drop for NOx and about 26 percent for Co2.”

With the air district under the same stay-at-home order that’s shut down the entire region, Roselius said they’re running an operation stripped down to just essential functions. Crunching the numbers to measure the slowdown’s impact on air quality would require the kind of resources that BAAQMD simply doesn’t have right now.