Decrease of NO2 between 2005 and 2011 in the Northeast of the United States (photos: NASA’s Aura Satellite)

This set of pictures shows the fallback in nitrogen dioxide (NO2) between 2005 and 2011. NO2 is a yellow-brown gas that is often used as an indicator for air pollution in general. It is produced during the combustion of fossil fuels in vehicle engines and coal power plants. Thanks to new regulation, air pollution in the US has decreased significantly.  These images represent the improvement seen in the northeast corridor of the U.S., from Boston to Richmond, where some of the largest absolute changes in NO2 have occurred.