Good news–there is much less nitrogen dioxide in the air over the United States than there was a decade ago, as can be seen in this remarkable animated satellite image. The images were produced by data collected by the Ozone Monitoring Instrument on NASA’s Aura satellite and you can clearly see how much the levels of this pollutant have decline from 2005 to 2011.

Nitrogen dioxide can cause respiratory problems by itself, besides also reacting with “ammonia, moisture, and other compounds to form small particles,” or particulates, that can worsen emphysema and other lung ailments, the EPA noted. The gas also contributes to the formation of ozone, which is an irritant and pollutant at ground level. NASA credits the improvement in air quality to improved fuel efficiency in cars and “technology to reduce emissions of nitrogen dioxide and sulfur dioxide from coal-fired power plants.” Generally, levels of nitrogen (and sulfur) dioxide began declining soon after enactment of the 1990 Clean Air Act Amendments, and have continued to fall. Overall, levels of nitrogen dioxide have declined by more than 50 percent since 2000, according to the EPA.

Of course, air quality isn’t perfect, and could get better. “While our air quality has certainly improved over the last few decades, there is still work to do–ozone and particulate matter are still problems,” NASA atmospheric scientist Bryan Duncan said. And about 142 million people still live in areas in the United States with unhealthy levels of air pollution, NASA noted.

New York air pollution

There has been a 32 percent decrease in nitrogen dioxide in New York City between the 2005-2007 (left) and 2009-2011 (right) periods.