Nasa confirms ozone hole shrinking due to CFCs ban

Nasa confirms ozone hole shrinking due to CFCs ban

The chlorofluorocarbons (CFCs) Strahan referred to are ozone-depleting chemicals that were once used in aerosol sprays, blowing agents for foams and packing materials, and refrigerants. When they rise to the stratosphere, they are broken down by ultraviolet solar radiation, releasing chlorine, which eats away at the ozone layer. Hydrochloric acid is a chemical that forms once chlorine has destroyed the ozone itself.

The ozone hole spurred countries and companies into action and the Montreal Protocol codified an agreement to slow down use of CFCs which appears to be working, reported.Hints of a recovery have often been followed by years in which ozone levels drop again.

The ozone layer acts as a protective shield around the Earth, absorbing the Sun's harmful ultraviolet radiation which can cause cancers, suppress the immune system in humans and damage plant life.

However, while past studies based on statistical analysis of the ozone hole's size have argued that the hole is recovering, the new study is the first to directly measure the chemical composition inside the ozone layer, confirming that the decline of CFCs is responsible for this.

The study, published Thursday in Geophysical Research Letters, reveals that a decline in ozone-depleting chemicals has resulted in 20 percent less depletion since 2005. Later amendments to the Montreal Protocol completely phased out production of CFCs.

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"During this period, Antarctic temperatures are always very low, so the rate of ozone destruction depends mostly on how much chlorine there is", Strahan said.

The study was published January 4 in the journal Geophysical Research Letters. Unlike other satellite instruments that rely on sunlight that bounces off molecules to measure atmospheric trace gases, MLS employs microwaves emissions that can identify and count trace gases even during the dark southern winter. Comparing hydrochloric acid levels with nitrous oxide levels-another gas that remains in the atmosphere-they determined chlorine's decline of 0.8 percent per year. By measuring hydrochloric acid levels each fall, scientists were able to gauge the amounts of chlorine in the ozone hole. Now, Strahan and colleagues report not only the first direct measurements that prove ozone depletion is decreasing but also that the decrease is caused by fewer CFCs in the atmosphere.

"This is very close to what our model predicts we should see for this amount of chlorine decline", Strahan said. The research spawned the idea that the hole was forming in the ozone layer, and inspired worldwide action.

"As far as the ozone hole being gone, we're looking at 2060 or 2080", Douglass said in a statement.

The hole in the ozone layer is getting smaller and smaller.