Arctic ozone loss at record levels: northern 'hole' comparable to early losses over Antarctica.
The Arctic observation raises concerns that parts of the Northern Hemisphere might periodically begin experiencing harmful levels of ultraviolet radiation in early spring, an international team reports October 27 in Nature.
"It was significantly worse than anything we have ever seen," says atmospheric chemist Geir Braathen of the World Meteorological Organization in Geneva, who was not involved in the new work. Typically, spring Arctic ozone depletion has maxed out at a drop of between 20 and 30 percent, he says. "But in 2011, we had a loss of around 40 percent."
In Antarctica, 70 percent of the ozone can disappear in springtime, Braathen says. In a 5- to 7-kilometer-thick band of the stratosphere, he says, ozone concentrations plummet to zero.
Arctic conditions have not gotten that bad, says Michelle Santee of NASA's Jet Propulsion Laboratory in Pasadena, Calif., one of 29 authors of the Nature paper.
Most Arctic ozone accumulates between 14 and 21 kilometers up, where concentrations hover around 4.5 parts per million much of the year. But in late March, "there was an approximately 2-kilometer altitude region where ozone fell to around 0.7 ppm," Santee says--"meaning the ozone was pretty much gone."
It takes four things to destroy much of the stratosphere's ozone: sunlight, very prolonged cold temperatures, a stable vortex of winds and the presence of special clouds that foster the transformation of benign chlorine molecules into ozone-vanquishing types. For the first time in the Arctic, all of these conditions aligned for months, says JPL atmospheric scientist and study coauthor Nathaniel Livesey.
Although prolonged cold spells in the stratosphere hit only every few years, those in recent winters have been increasingly extreme, says Ross Salawitch of the University of Maryland in College Park, and there's some concern that a progressive warming at Earth's surface is responsible.
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|Article Type:||Brief article|
|Date:||Nov 19, 2011|
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