Is the ozone hole was recovering? Maybe not. The protective atmospheric layer of ozone around our planet has been thinning over Antarctica for many years. New satellite data indicates the 2008 ozone hole is larger both in size and ozone loss than 2007 but is not as large as the record year of 2006. This year the area of the thinned ozone layer over the South Pole reached about 27 million square kilometers, compared to 25 million square kilometers in 2007 and a record ozone hole extension of 29 million square kilometers in 2006, which is about the size of the North American continent. Ozone is a protective atmospheric layer found about 25 kilometers in altitude that acts as a sunlight filter, shielding life on Earth from harmful ultraviolet rays. A thinner ozone layer can increase the risk of skin cancer and cataracts and harm marine life. What causes the ozone layer to change from year to year, and if CFC’s have been banned, why isn’t the ozone recovering?
The depletion of ozone is caused by extreme cold temperatures at high altitude and the presence of ozone-destructing gases in the atmosphere such as chlorine and bromine. Most of these gases originate from man-made products like chlorofluorocarbons (CFCs), which were phased out under the 1987 Montreal Protocol. But they continue to linger in the atmosphere.
Depending on the weather conditions, the size the Antarctic ozone hole varies every year. As the polar spring arrives in September or October, the combination of returning sunlight and the presence of so-called stratospheric clouds (PSCs) over the Antarctic leads to a release of highly ozone-reactive chlorine radicals present in the atmosphere that break ozone down into individual oxygen molecules. A single molecule of chlorine has the potential to break down thousands of molecules of ozone.
Colder temperatures in the stratosphere over Antarctica, combined with a high formation rate of PSCs caused more lingering chlorine radicals to be released, making the current hole one of the largest. 2006 saw the largest hole. A unit of measurement called a Dobson Unit describes the thickness of the ozone layer, and this year (2008) about 120 Dobson Units were observed compared to around 100 Dobson Units in 2006.
The analysis is based upon the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) atmospheric sensor onboard ESA’s Envisat, the Global Ozone Monitoring Experiment (GOME) aboard ESA’s ERS-2 and its follow-on instrument GOME-2 aboard EUMETSAT’s MetOp.