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CC14 still eating up our ozone nearly 30 years after it was banned

Rocket carries NASA's Aura satellite into Polar orbit to study the Earth's ozone, air quality and climate in 2004.
Rocket carries NASA's Aura satellite into Polar orbit to study the Earth's ozone, air quality and climate in 2004.
Photo by U.S. Air Force/Getty Images

Although the chemical compound Carbon tetrachloride (CCl4), (once used in applications such as dry cleaning and as a fire-extinguishing agent, etc) other chlorofluorocarbons were banned under the 1987 Montreal Protocol, new research has found emissions of CC14 ranged approximately 39 kilotons per year between 2007-2012. This is nearly 30% of the peak emissions before the international treaty went into effect. As of 2008, CCl4 accounted for about 11% of chlorine available for ozone depletion. While experts report that this is “not enough to alter the decreasing trend of ozone-depleting substances,” they want to know the source of these mysterious emissions.

“People believe the emissions of ozone-depleting substances have stopped because of the Montreal Protocol," commented, chief scientist for atmospheres at NASA's Goddard Space Flight Center, Paul Newman, who co-authored the study. "Unfortunately, there is still a major source of CCl4 out in the world."

"We are not supposed to be seeing this at all," added Qing Liang, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study. "It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources. The big question is whether there is a physical CCl4 loss process we don't understand, or are there emission sources that go unreported or are not identified?"

Liang also went on to state that “atmospheric concentrations of the compound should have declined at an expected rate of 4% per year. Yet ground observations showed only a 1% decline per annum.”

In order to learn more about the discrepancy, Liang and scientists at the National Oceanic and Atmospheric Administration’s Earth System Research Lab and NOAA’s Copperative Institute for Research in Environmental Studies at the University of Colorado in Boulder, used NASA's 3-D GEOS Chemistry Climate Model and data from global networks of ground-based observations to measure CC14 levels. The model results also revealed that the chemical stays in the atmosphere 40% longer than previously believed.

The research was published online in the Aug. 18 issue of Geophysical Research Letters.

Note: While many people know about NASA’s projects regarding space exploration, it is important to point out that the Space Agency is constantly monitoring the Earth's “vital signs” from the ground, as well as air and space via satellites as a means of studying our planet’s interconnected and ever changing natural systems.

For more information about the hole in the ozone layer above Antarctica visit

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