A Hole Lot Smaller

20%—The approximate decline in ozone depletion during recent Antarctic winters compared to 2005, according to new research published in Geophysical Research Letters that also confirms the decrease is the result of declining levels of chlorofluorocarbons (CFCs). Susan Strahan and Anne Douglass of NASA Goddard Space Flight Center are the first to use chemical composition measurements taken directly from inside the ozone hole to confirm the reduction as well as the cause (previous studies focused on changes in the ozone hole’s size). Strahan and Douglass studied daily Southern Hemisphere wintertime (early July to mid-September) measurements for 2005–16 of ozone, hydrochloric acid, and nitrous oxide collected by NASA’s Aura satellite. During the southern winter, “Antarctic temperatures are always very low, so the rate of ozone destruction depends mostly on how much chlorine there is,” Strahan explains. “This is when we want to measure ozone loss.” After determining that loss was declining, they confirmed the cause was a decrease in CFCs by looking at hydrochloric acid and nitrous oxide levels, which are both indicators of chlorine content. Their research showed that chlorine levels decreased by an average of about 0.8% per year. Strahan notes that the decrease in ozone depletion is similar to their model predictions for that amount of chlorine decline, which “gives us confidence that the decrease in ozone depletion through mid-September . . . is due to declining levels of chlorine coming from CFCs. But we’re not yet seeing a clear decrease in the size of the ozone hole because that’s controlled mainly by temperature after mid-September, which varies a lot from year to year.” Douglass notes that because of the long lifespan of CFCs, “we’re looking at 2060 or 2080” before the ozone hole closes completely, “[a]nd even then there might still be a small hole.” [Source: NASA]
 

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