New NASA satellite data has revealed the location of 39 major unreported and human-made sources of toxic sulfur dioxide emissions, a health hazard that is known to contribute to air pollution and play a role in acid rain.
Currently, scientists monitor sulfur dioxide using emission inventories based on ground-measurements and factors such as fuel usage. These inventories form the basis of regulatory policies that aim to improve air quality, although in order to be effective, scientists must also know the locations of the pollution sources.
"We now have an independent measurement of these emission sources that does not rely on what was known or thought known," said Chris McLinden of Environment and Climate Change Canada in Toronto and lead author of the study. "When you look at a satellite picture of sulfur dioxide, you end up with it appearing as hotspots - bull's-eyes, in effect - which makes the estimates of emissions easier."
The current study revealed 39 unreported emissions sources using NASA satellite data from the year 2005 to 2014. These sources include coal-burning power plants, smelters and oil and gas operations - mostly in the Middle East but also in Mexico and Russia.
In addition to the unreported sources, the data reveals that sometimes, emissions from known sources in these regions were actually two to three times lower than estimates taken from satellite images.
The team also discovered 75 natural sources of sulfur dioxide in the form of non-erupting volcanoes that gradually leak toxic gas into the atmosphere each year. Although scientists were previously aware of such volcanoes, many of them are in remote locations, making them difficult to monitor.
"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 Nickolay Krotkov of NASA's Goddard Space Flight Center in Greenbelt, Md., and co-author of the study.
Krotkov and the team were able to pinpoint the undiscovered locations of sulfur dioxide emissions using a new computer program that was able to accurately detect the chemical when it was dispersed and diluted by winds. Using satellite data to estimate wind strength and direction, the team was able to trace the pollutant back to its source location and estimate how much of it was emitted.
"The unique advantage of satellite data is spatial coverage," said Bryan Duncan, who was not involved in the study and also of Goddard. "This paper is the perfect demonstration of how new and improved satellite datasets, coupled with new and improved data analysis techniques, allow us to identify even smaller pollutant sources and to quantify these emissions over the globe."
The findings were published in the May 30 issue of the journal Nature Geoscience.
