Analyzing nine years' worth of data collected by NASA’s satellite Aura, U.S. and Canadian scientists have discovered 39 unreported major sources of sulfur dioxide.
Clusters of coal-burning power plants, smelters, and other oil and gas installations were located mostly in Middle Eastern countries but also in Mexico and Russia.
The scientists also said that reported emissions from known sources were sometimes much lower than estimates based on satellite-gathered data.
Environment and Climate Change Canada, a part of the Canadian government, said that as much as 12 percent of all human-made air pollutants are unreported or underreported.
In addition to that, scientists pinpointed 75 previously unknown natural sources of sulfur dioxide, mostly dormant volcanoes.
According to NASA scientist Nick Krotkov, discoveries were facilitated by improvements in computer processing of data collected by the Aura satellite.
Results of the study were published in the online science magazine nature.com.