Nitrogen dioxide, averaged yearly from 2005-2011, has decreased across the United States.
Image Credit: NASA Goddard's Scientific Visualization Studio/T. Schindler.

A team of scientists have used the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite to confirm major reductions in the levels of a key trace gas generated by coal power plants in the eastern United States. The trace gas, sulfur dioxide, contributes to the formation of acid rain and can cause serious health problems.

Image Credit: Jesse Allen, NASA Earth Observatory.

In 1973, an astronaut aboard America’s first space station took an historic photograph over the Los Angeles basin. Viewed from the NASA Skylab, the sprawling California metropolis was almost completely obscured by smog from car exhaust and emissions from factories and oil refineries.