Ozone hole modest despite optimum conditions for ozone depletion

The ozone hole that forms in the upper atmosphere over Antarctica each September was slightly above average size in 2018. Colder-than-average temperatures in the Antarctic stratosphere created ideal conditions for destroying ozone this year, but declining levels of ozone-depleting chemicals prevented the hole from as being as large as it would have been 20 years ago. Chlorine levels in the Antarctic stratosphere have fallen about 11 percent from the peak year in 2000. This year's colder temperatures would have given us a much larger ozone hole if chlorine was still at levels. The annual ozone hole reached an average area coverage of 8.83 million square miles (22.9 square kilometers) in 2018, almost three times the size of the contiguous United States. It ranks 13th largest out of 40 years of NASA satellite observations. Nations of the world began phasing out the use of ozone-depleting substances in 1987 under an international treaty known as the Montreal Protocol. The 2018 ozone hole was strongly influenced by a stable and cold Antarctic vortex—the stratospheric low-pressure system that flows clockwise in the atmosphere above Antarctica.