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DENVER — Scientists have found that oil and gas fields along Colorado's Front Range mountains have been emitting three times more methane and nearly eight times more cancer-causing benzene than previously thought.

A study by the National Oceanic and Atmospheric Administration and partly supported by the Environmental Defense Fund is based on data gathered in 2012 from aircraft flying over drilling zones north of Denver.

For years, health and environmental officials have estimated air pollution primarily by measuring ground-level sources. State agencies didn't begin monitoring methane until 2012, and the new study marks one of the first efforts to investigate pollution in the atmosphere above ground level.

"We're trying to provide independent information on air pollution to help decision-makers and industry minimize their impacts," lead scientist Gabrielle Petron told The Denver Post (http://bit.ly/1qieeMp ). "If the energy industry keeps expanding operations on the Front Range, we need to know we will have a good handling of the emissions."

The oil and gas industry is the main source of methane in the United States, but industrial livestock operations and landfills also emit the gas. Researchers said they accounted for those numbers and subtracted.