Study finds reduction in chemicals that created hole in Earth's ozone layer
Lower levels of atmospheric chlorine over Antarctic show international ban on CFCs is working.

Laurel Kornfeld | Apr 19, 2018

A first-of-its-kind study of satellite data collected between 2005 and 2016 shows a reduction in the amount of chlorine, the chemical responsible for atmospheric ozone depletion, in the atmosphere over Antarctica.

First detected in the mid-1980s, the ozone hole over Antarctica was found to be caused by man-made chlorofluorocarbons (CFCs), specifically produced by their main byproduct, chlorine.

Earth's ozone layer protects the planet from the Sun's ultraviolet rays, which can damage plant life and cause both cancer and cataracts in humans.

Satellites have observed the Antarctic ozone hole grow and shrink over many years, but this study used data collected on ozone over Antarctica by the Earth observation Aura satellite's Microwave Limb Sounder (MLS) instrument to detect hydrochloric acid, which is produced when chlorine atoms react with methane and then bond with hydrogen.

During Antarctic summers, CFCs break down into chlorine, which in turn break down ozone atoms. In the colder winter months, the chlorine, having broken down all the atmospheric ozone, reacts with methane to form hydrochloric acid, which MLS is capable of measuring.

"During this period, Antarctic temperatures are always very low, so the rate of ozone destruction depends mostly on how much chlorine there is. This is when we want to measure ozone loss," explainedatmospheric scientist Susan Strahan of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"By mid-October (Antarctic spring), all the chlorine compounds are conveniently converted into one gas, so by measuring hydrochloric acid, we have a good measurement of the total chlorine," Strahan said.

Discovery of the ozone hole led to an international ban on CFCs. According to this latest study, whose findings have been published in the journal Geophysical Research Letters, ozone depletion decreased by 20 percent between 2005 and 2016, a level that matched computer model predictions.

Chlorine levels declined approximately 0.8 percent per year during the study's 11 years.

While the ozone hole is gradually healing, complete recovery will not occur until sometime between 2060 and 2080 because CFCs remain in the atmosphere between 50 and 100 years, noted fellow Goddard atmospheric scientist Anne Douglass, who took part in the study.

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