Earth's atmosphere contains an unexpectedly large amount of an ozone-depleting compound from an unknown source decades after the compound was banned worldwide.
The compound, carbon tetrachloride, was used in applications such as dry cleaning and as a fire-extinguishing agent, until its regulation in 1987 under the Montreal Protocol along with other chlorofluorocarbons that destroy ozone and contribute to the ozone hole over Antarctica. Parties to the Montreal Protocol reported zero new emissions between 2007-2012.
However, new research led by Qing Liang at NASA's Goddard Space Flight Center in Greenbelt, Maryland, shows that worldwide emissions of carbon tetrachloride average 39 kilotons per year – approximately 30 percent of peak emissions prior to the international treaty going into effect. Now that scientists have quantified the emissions they can begin investigating where they are coming from. Are there industrial leakages, large emissions from contaminated sites, or some other unknown source?
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 18.104.22.168.0