Americans are breathing less air pollution than before.
Specifically, they're inhaling less nitrogen dioxide, a gas that can cause respiratory problems, according to a new time-lapse released by NASA. New satellite images showing concentrations of the gas, averaged yearly between 2005 and 2011, show a reduction in air pollution across the country, especially in major cities.
Nitrogen dioxide, one of the six common pollutants regulated by the Environmental Protection Agency, serves as a good proxy for air pollution in general. The gas is produced by gasoline-fueled vehicles and coal-powered plants.
The photos, released this week, come from the Ozone Monitoring Instrument, located aboard NASA's Aura satellite, which has been in orbit for 10 years. Blue and green denote lower concentrations of nitrogen dioxide, while orange and red areas indicate higher concentrations of the gas.
In 2005, pollution built up significantly along the East Coast, from Richmond all the way up to Boston. By 2011, there was much less, even though there were more people—and cars—in big cities. From 2005 to 2007, and then again from 2009 to 2011, the level of nitrogen gas decreased by 42 percent in Atlanta, 32 percent in New York City, and 22 percent in Denver.
Experts attribute the reduction in air pollution to federal regulations of emissions, improvements in technology, and other factors. While that's all well and good, the picture is not perfect. According to EPA, about 142 million people still live in areas in the U.S. with unhealthy levels of air pollution.