1. Decades ago the use of carbon tetrachloride (CCl4) became strictly regulated.
This satellite image from 2006 shows the largest the hole in the ozone layer has been. The purple and blue areas are where the ozone concentration is lowest, and red and yellow where it’s higher.
2. CCl4 used to be widely used in refrigerators, dry cleaning, fire extinguishers, and aerosol cans, according to the EPA.
The invisible gas was finally restricted under 1987’s international treaty, called the Montreal Protocol, and globally banned in recent years to protect our fragile ozone layer from further depletion.
4. But NASA says 39,000 metric tons of CCl4 were released every year in that time period.
And it’s still lingering in the atmosphere. The study, published in Geophysical Research Letters, states that UNEP’s estimates “cannot be reconciled with the observed slow decline of atmospheric concentrations.”