NASA satellite data shows that the New York City area has seen a 32 percent decrease in nitrogen dioxide between 2005 and 2007 (left) and 2009 and 2011 (right). Anyone living in a major U.S. city for the past decade may have noticed a change in the air. People in major urban areas are breathing less nitrogen dioxide, a yellow-brown gas that can cause respiratory problems. The improvement is apparent in new images that demonstrate the reduction of air pollution across the country. After ten years in orbit, the satellite has been gathering data sufficiently long to show that nitrogen dioxide pollution, averaged yearly from 2005 to 2011, has decreased across the United States.