NASA - National Aeronautics and Space Administration

Each year, the depleted region in Earth's protective ozone layer over the Antarctic, or "ozone hole," reaches its largest size during a period in September. Data from a NASA satellite are now in, and images created from the data reveal the extent of the hole in 2007 was about average when compared to measurements from the last few decades.

Image right: The area of the Antarctic atmosphere called the "ozone hole" opens up each year in mid-August and peaks in September. This year the ozone hole reached its peak on Sept. 13, appearing blue and purple in this image created with data collected from the Ozone Monitoring Instrument (OMI) aboard the NASA Aura satellite. NASA atmospheric scientist Paul Newman describes this year's hole as average, peaking at 9.7 million square miles, roughly the size of North America. + Click for larger image Credit: NASA

Data from NASA's Earth-observing Aura satellite show that the ozone hole peaked in size on Sept. 13, reaching a maximum area extent of 9.7 million square miles ­ just larger than the size of North America. That's "pretty average," says Paul Newman, an atmospheric scientist at NASA Goddard Space Fight Center, when compared to the area of ozone holes measured over the last 15 years. Still, the extent this year was "very big," he says, compared to 1970s when the hole did not yet exist.

In comparison, 2002 and 2004 turned up weak ozone holes with maximum areas of about 8.3 million and 8.7 million square miles, respectively. The hole in 2006, however, reached a record-breaking maximum area of 11.4 million square miles.

The ozone hole reaches its maximum area in September when cold temperatures and sunlight beginning to appear over the Antarctic horizon and start to drive chemical reactions that destroy ozone. The chlorine in these reactions comes from manmade chlorofluorocarbons (CFCs). By October, the ozone-destroying chemical reactions stop, and the hole shrinks in area and depth. During the period from October to December, the ozone depleted region is "stirred up like a can of paint" into the mid-latitudes, depleting atmosphere ozone there.

Despite successful measures that have stopped production of CFCs, scientists don¹t expect to see the hole significantly reduce in size for about another decade, Newman says. This is due to the long lifetimes of CFCs already in the atmosphere, ranging from 40 to 100 years. Full recovery is expected in about 2070. But even that prediction is tentative, he says, because scientists remain uncertain about how a changing climate will come into play, as warming temperatures could act to speed up recovery of the ozone hole.

 

 

Kathryn Hansen
Goddard Space Flight Center