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Satellites observed the largest ozone hole over Antarctica in 2006. Purple and blue represent areas of low ozone concentrations in the atmosphere; yellow and red are areas of higher concentrations. / NASA

It's not supposed to be up there.

Our atmosphere "contains an unexpectedly large amount of an ozone-depleting compound from an unknown source, decades after the compound was banned worldwide," reports a NASA study out this week.

Before its use was supposedly banned in 1987 by an international treaty, the compound, carbon tetrachloride (CCI4), was produced in large quantities to make refrigerants and propellants for aerosol cans, as a solvent for oils, fats, lacquers, varnishes, rubber waxes, and resins, and as a dry cleaning agent, according to the Environmental Protection Agency.

"We are not supposed to be seeing this at all," said Qing Liang, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., and lead author of the study.

Its use was banned under the Montreal Protocol, along with other chlorofluorocarbons that destroy ozone and contribute to the ozone hole over Antarctica.

Ozone blocks harmful ultraviolet energy from reaching the Earth.

"Carbon tetrachloride is not a naturally occurring compound," said Liang in an e-mail. "But the recent emissions could be from unknown chemical production processes, such as mixing soap and sodium hypochlorite, or soil releases of CCl4 from old contaminated dump sites."

"Based on our estimate, currently, every year about 39 kilotons of CCl4 are emitted into the atmosphere, compared to about 120 kilotons released into the atmosphere every year during its peak emission years," she said.

"These are new annual emissions, not aged emissions accumulated in the atmosphere," she added.

Though this amount is not enough to halt the decreasing trend of ozone-depleting substances, scientists want to know the source of the unexplained emissions, the study notes.

"People believe the emissions of ozone-depleting substances have stopped because of the Montreal Protocol," said Paul Newman, chief scientist for atmospheres at Goddard Space Flight Center, and a co-author of the study. "Unfortunately, there is still a major source of CCl4 out in the world," he said.

The study was published online in the Aug. 18 issue of Geophysical Research Letters, a journal of the American Geophysical Union.



Copyright 2014USAToday

Read the original story: Ozone-depleting compound remains in our atmosphere

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