NASA Probing Why Ozone Hole Is Smaller

The so-called hole in the stratospheric ozone layer above Antarctica this year peaked at about the same size it reached in the past two years, NASA reports. But this year’s hole—an area of depleted ozone that forms each year in August and September—was smaller than the holes that formed from 1998 to 2006, NASA reports. Researchers are working to determine why the ozone hole has been smaller during the past decade, the agency says. Increases in stratospheric temperature over Antarctica could be the reason, NASA says, because ozone depletion occurs more rapidly at colder temperatures. Another possibility is that the concentration of chlorine, which breaks down ozone in the stratosphere, is dropping because of international efforts to curb production and use of chlorofluorocarbons and other chemicals linked to ozone depletion. Ground-based and satellite measurements indicate that chlorine levels are falling, NASA says, but temperature analyses for the stratosphere over Antarctica aren’t reliable enough to determine long-term trends.