How the pandemic is changing air pollution levels.

With more of us staying inside and off the roads, cities around the globe are reporting less air pollution.
In the United States, Washington, D.C., is experiencing its cleanest spring air in 25 years, while Los Angeles – once ranked as having the worst air quality in the country – is now boasting some of the best in the world.
Los Angeles air quality has improved dramatically with the economic slowdown and stay-at-home orders resulting from the coronavirus pandemic.  
It's likely a response to fewer cars on the road. 
"Nitrogen dioxide is formed from the burning of fossil fuels," Stauffer said. "So, think about the burning of gasoline in your car engine. It also comes from electricity power generation. So, it's emitted in fairly significant quantities, especially around cities and areas with high amounts of traffic."
Lelia Hawkins, a professor at Harvey Mudd College in Claremont, California, who specializes in air pollution and climate change, said, "We see the benefits of better practices right away just like we're seeing now. …
"People are asking, you know, is this a silver lining? And my answer is yes and no. It's great to have the cleaner air, but the devastating economic consequences of this crisis are not something that anyone would choose.
"On the bright side, this is a situation [that] will help air pollution scientists like me understand the role that various activities play in our daily exposure, and that will help us be strategic about policies we put in place."
But in the meantime, Hawkins said, these clearer skies should lead to a clearer understanding of our planet.
"The fact that we are able to see clear skies and a lot of places, some that haven't seen clear skies in a very long time, it shows us two things: One, we really are having an impact on our environment, and small changes that we make – in this case large changes, but even small changes – that are targeted can clean up the atmosphere;  and two, that it can happen really rapidly."