A NASA satellite confirmed a sharp decline in pollution from coal power plants in the eastern United States.

Using the Ozone Monitoring Instrument (OMI) on the satellite, a group of scientists at NASA found a 40 percent decline in sulfur dioxide levels since 2005, consistent with the 46 percent reduction observed by ground-based instruments inside power plant smokestacks, according to a statement on NASA's website Thursday.

Sulfur dioxide is considered by scientists a key air pollutant that contributes to the formation of acid rain and poses serious health problems.

"This is the first time scientists have observed such subtle details over the United States, a region of the world that in comparison to fast-growing parts of Asia now has relatively modest sulfur dioxide emissions," NASA said in a statement.

The agency noted that sulfur dioxide pollution was quite severe in the U.S. just a few decades ago but that levels have dropped by about 75 percent since the 1980s.

NASA's scientists attribute the decline in sulfur dioxide to the Clean Air Interstate Rule, a rule passed by the EPA in 2005 that put a limit on sulfur dioxide emissions for utility companies.

Many power plants in the United States have installed desulfurization devices and taken other steps like trading pollution credits to adjust to the Federal Government's rules.

"What we’re seeing in these satellite observations represents a major environmental accomplishment," said Bryan Bloomer, an Environmental Protection Agency (EPA) scientist familiar with the new satellite observations.

NASA plans to use its satellite to monitor levels of this and other important pollutants that coal power plants release in other parts of the world.

Vitali Fioletov, a scientist based in Toronto at Environment Canada, and his colleagues developed a new mathematical approach that made the satellite measurements a reality. The approach centers on averaging measurements within a 30 miles radius (50 km) of a sulfur dioxide source over several years, according to NASA.

The technique allowed them to pinpoint the sulfur dioxide signals from the 40 largest sulfur dioxide sources in the United States - generally coal power plants that emit more than 70 kilotons of sulfur dioxide per year.

The scientists observed major declines in sulfur dioxide emissions from power plants in Alabama, Georgia, Indiana, Kentucky, North Carolina, Ohio, Pennsylvania and West Virginia by comparing levels of the pollutant for an average of the period 2005 to 2007 with another average from 2008 to 2010, NASA informs.

OMI, a Dutch and Finnish built instrument, was launched in 2004, as one of four instruments on the NASA Aura satellite, and can measure sulfur dioxide more accurately than any satellite instrument flown to date.