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OUT OF THIS WORLD | Earth, Space and Everything In-Between - a daily journey through weather, space and science with meteorologist/science writer Scott Sutherland

NASA finds first direct evidence the Ozone Hole is healing

Scott Sutherland
Meteorologist/Science Writer

Saturday, January 6, 2018, 16:27 - The 2017 Antarctic ozone hole was the smallest seen in nearly 30 years, and NASA scientists now have direct evidence that the Montreal Protocol, enacted to protect the ozone layer, is actually succeeding!

In September of 2017, the Antarctic ozone hole reached its smallest maximum area since 1988, dropping below 20 million square kilometres (7.7 million square miles) for the first time in 29 years. While this partly due to warmer temperatures measured over the Antarctic, according to NASA, based on a new study published on January 4, we can say, with confidence, that it's not just the unusually warm weather producing this effect.

Reaching a maximum area of 19.6 million km2 (7.6 million square miles), on September 11, 2017, the Antarctic ozone hole was 10 million km2 (3.9 million square miles) smaller than the largest ozone hole ever seen, on September 24, 2006.

Antarctic ozone hole maxima, from 2017 (left) and 2006 (right). The abrupt discontinuity in the 2017 plot is due to the orientation of the ozone hole rotating as the satellite gathered its data over the full 24 hour period. Credit: NASA Ozone Watch/Scott Sutherland

According to the authors of this study, Susan Strahan and Anne Douglass, who are both atmospheric scientists at NASA's Goddard Space Flight Center, in Greenbelt, Maryland, measurements taken over the Antarctic by NASA's Aqua satellite - of ozone, nitrous oxide and hydrochloric acid - show that ozone depletion is definitely in decline.

Direct ozone measurements, taken by Aqua from 2005-2016, show that there is less ozone disappearing over the southern winter. It's not a case of each annual ozone hole being smaller than the last, since there can be fluctuations from year to year, but the trend definitely reveals the decline.

Since temperature has a large influence over ozone depletion (colder = more depletion, warmer = less depletion), a way was needed to separate out the cause of this decline. For this, Strahan and Douglass turned to Aqua's measurements of two chemicals that are found in the stratosphere. The first was hydrochloric acid (HCl), which is one of the end products of CFCs destroying ozone, and thus would be found in abundance inside each annual ozone hole and would be an indicator of exactly how much chlorine was present to cause ozone depletion. The second was nitrous oxide (N2O), another long-lived chemical that is capable of reaching the stratosphere, which acts as an excellent baseline for comparison to CFCs because its concentration is not declining, and it is affected by the same atmospheric motions that would impact measurements of hydrochloric acid.

If CFC concentrations in the stratosphere were not declining, and thus the smaller ozone holes were only due to temperature fluctuations, Strahan and Douglass would have found that the concentrations of HCl and N2O were relatively stable compared to one another. However, their study found that hydrochloric acid concentrations in the ozone hole were declining by comparison, by an average of 0.8 per cent per year.

"We see very clearly that chlorine from CFCs is going down in the ozone hole, and that less ozone depletion is occurring because of it," Strahan said in a NASA statement.

Strahan discusses the study and its findings in the video below.

It was over 30 years ago that the United Nations met to sign the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. This agreement, which went into effect in 1989, phased out the production of chlorofluorocarbons, in favour of chemicals that would perform the same function, but not have as large an impact on stratospheric ozone. Although there have been definite signs of recovery for the ozone hole over the years, it had still been difficult to show that this recovery was a direct result of CFC regulations.

With this study, though, we have the first direct evidence of the success of the Montreal Protocol.

Source: NASA

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