Good news for the ozone hole: it didn’t surprise scientists.
Each September, the ozone hole forms over Antarctica. This year, the hole grew to 23 million square kilometres — more than twice the size of Canada — before beginning its recovery, according to the National Oceanic and Atmospheric Administration.
READ MORE: Ozone hole finally beginning to heal, study finds
Ozone is found in small amounts in Earth’s upper atmosphere. The ozone layer — located about 15 to 30 kilometres above Earth — protects us from harmful ultraviolet radiation which has been linked to skin cancer and can suppress human immune systems. It’s also harmful to vegetation.
“This year we saw an ozone hole that was just below average size,” said Paul A. Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “What we’re seeing is consistent with our expectation and our understanding of ozone depletion chemistry and stratospheric weather.”
The average size of the hole since 1991 is 26 million square kilometres. In 2015, the hole grew to 28 million square kilometres, mainly as a result of cooler temperatures in the stratosphere where sunlight reacted with man-made chemicals such as chlorine and bromine.
There was deep concern in the 1980s over the thinning of the ozone layer. The layer is measured in Dobson Units (it’s the measurement unit for the total number of molecules of ozone between the surface and space) and until 1979, had never dipped below 200. However, by 1985 it had plummeted to 124.
The decimation of the layer was believed to be in large part to the amount of chlorofluorocarbons (CFCs) which are found in industrial aerosols. When the CFCs enter the upper atmosphere, they break down into other substances, including chlorine which react with the oxygen molecules and tear apart the ozone molecule.
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