Banned Compound Still Depleting Our Ozone

A compound that was banned worldwide decades ago is still present in the Earth's atmosphere and depleting our ozone, according to new NASA research.

Carbon tetrachloride (CCl₄), the ozone-depleting compound in question, was used in dry cleaning and as a fire-extinguishing agent, but once it was realized that it diminished Earth's ozone, it was banned in the 1987 Montreal Protocol. And from 2007-2012, the Montreal Protocol reported zero new CCl₄ emissions.

However, the new research surprisingly shows worldwide emissions of CCl₄ average 39 kilotons per year, approximately 30 percent of peak emissions prior to the international treaty going into effect.

"We are not supposed to be seeing this at all," Qing Liang, an atmospheric scientist at NASA's Goddard Space Flight Center, said in a news release.

"It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl₄ sources," she added.

As of 2008, CCl₄ accounted for about 11 percent of chlorine available for ozone depletion. This is not enough to significantly add to the already decreasing ozone, but nonetheless scientists are determined to figure out where these emissions are coming from.

Based on the CCl₄ emissions reported between 2007 and 2012, atmospheric concentrations of the compound should have dropped four percent per year; but, for some reason they only declined by one percent per year.