Banned chemical still depleting the ozone, says NASA

Carbon tetrachloride, banned under Montreal Protocol, still lingering in atmosphere

By Sonalika Sinha
Published: Friday 22 August 2014

imageSomeone somewhere is wrecking the Earth’s ozone layer. Carbon tetrachloride, or CC14, that was used as dry cleaning and fire-extinguishing agent, was banned worldwide in 1987 under the Montreal Protocol. It destroys the ozone and contributes to the ozone hole over Antarctica. But a NASA research shows that unexpectedly large quantities of CC14 are still lingering in the earth’s atmosphere.

Between 2007 and 2012, parties to the Montreal Protocol had reported zero CC14 emissions. But during its research, NASA found an average of 39 kilotonnes of CCl4 was being emitted worldwide every year. This is about 30 per cent of peak emissions prior to the international treaty going into effect.

With zero CCl4 emissions between 2007 and 2012, atmospheric concentration of the compound should have declined at an expected rate of 4 per cent per year. But CCl4 concentration in the atmosphere is falling by only 1 per cent per year. The study also found that the chemical stays in the atmosphere 40 per cent longer than previously thought.

Pointing to an unidentified ongoing current source of CC14, Qing Liang, lead author of the study, says, “It is apparent that there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources.” Liang is atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The study was published online in the August 18 issue of the journal Geophysical Research Letters.


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