A NASA satellite discovered 39 major — and unreported — man-made sources of toxic sulfur dioxide emissions.

Sulfur dioxide (SO2), which is a recognized health threat, plays a contributing role in the development of acid rain. SO2 is also one of the six pollutants that the U.S. Environmental Protection Agency (EPA) regulates.

A new satellite-based method allowed a team of scientists across various affiliations to locate new sources of man-made SO2 emissions.

Lead author and atmospheric scientist Chris McLinden said that satellite images of sulfur dioxide activities appear as "hotspots." McLinden, who is from the Climate Change Canada in Toronto, added that these make estimating emissions easier.

The findings provided new independent SO2 emission sources that do not rely on current monitoring techniques. At present, monitoring SO2 activities include analysis of emission records. These data are taken from ground measurements as well as other factors including fuel usage.

However, in order to create a complete and precise SO2 emissions records, governments and industries must first determine their exact locations.

Teams from the University of Maryland and NASA in the United States and Dalhousie University and the Climate Change in Canada analyzed satellite data taken from 2005 to 2014.

The satellite's spatial coverage coupled with new data analysis methods allowed the teams to zone in even on the smaller sources of pollutants.

Among the 39 unreported SO2 emissions they found included groups of power plants using coal as well as gas and oil operations. The areas included Mexico, Middle East and several areas in Russia.

Some of the reported SO2 emission activities in these regions were actually two to three times lesser than the estimates taken by satellite.

But the total amount of underreported and unreported SO2 sources make up 12 percent of all man-made SO2 emissions.

"Quantifying the sulfur dioxide bull's-eyes is a two-step process that would not have been possible without two innovations in working with the satellite data," said study co-author and atmospheric scientist Nickolay Krotkov from NASA's Goddard Space Flight Center.

The new research was published in the journal Nature Geoscience on May 30.

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