Ozone Hole is Back and Big

Sept. 7 -- Remember the ozone hole? Last year it closed by November but scientists report it's back and for the second year in a row, it appears to be reaching record size.

Cold weather, giant areas of low and high pressure, high levels of human-made gases and approaching spring in the Antarctic have again provided the right mix of conditions to broaden a yawning gap of the protective layer of ozone in the stratosphere.

Scientists report the hole has cracked open to more than 15 million square miles or about the size of the entire continent of North America. That's only two to three million square miles short of the hole's record size last year, and it's expected to keep on growing.

The stratosphere is a layer of atmosphere about 6 to 30 miles above the surface that contains the chemical compound known as ozone. While at ground level ozone is an unhealthy pollutant, in the stratosphere it plays a vital role in absorbing harmful ultraviolet radiation from the sun.

Over the past 20 years, concentrations of this ozone layer have thinned due in part to human-made gases released into the atmosphere including those known as chlorofluorocarbons or CFCs.

Could Open Over Chile

It was about this time last year that locals in southern Chile were warned to don wide-brimmed hats and sunglasses to shield themselves from radiation beaming through a widening ozone hole that had stretched over southern portions of the country. This year scientists say Chileans might again need to seek cover.

"Conditions are ripe for a large hole," says Paul Newman, an atmospheric scientist at NASA Goddard Space Center in Maryland. "There's a good chance one lobe could pass over the southern coast of Chile this year."

Since the 1970s, scientists have observed the ozone hole begin to open by late August and then close by November or December. Its annual reappearance is due to a combination of cold air and sunlight that are both present in the Antarctic during that window.

Cold weather in the Antarctic triggers ice clouds to form in the stratosphere. The clouds provide a surface layer that converts CFCs, accumulated after decades of widespread use of items like aerosol spray cans and CFC-containing air conditioners and refrigerators, into new forms. Add sunlight and these forms become chlorine atoms which then break down the ozone layer.