The hole covered almost 800,000 square miles and allowed high levels of harmful ultraviolet radiation to hit large swaths of northern Canada, Europe and Russia this spring, the scientific team said. “The loss in 2011 was twice that in the two previous record-setting Arctic winters, 1996 and 2005,” says Nathaniel Livesey of the Jet Propulsion Laboratory in Pasadena, California.
The study used U.S. and European satellites, along with ground stations and scientific balloons to find and track the hole. The balloons, known as ozone sondes, take hundreds of samples on their way from the ground to 18 miles up in the atmosphere. Those measurements helped confirm that chlorine-based pollutants in the stratosphere, 11 to 12 miles above the ground have triggered a process that converts the chlorine into a chemically active compounds which destroy the ozone molecules.
Extreme and prolonged cold in the stratosphere last winter and spring sped up and enhanced the chemical reactions that destroy the ozone, says co-author Michelle Santee, of the Jet propulsion Laboratory at the California Institute for Technology. Her group was monitoring the hole in the Arctic from space, using satellites.
Ozone-destroying chlorine compounds have been banned internationally, but they are so “long lived” the scientists expect them to stay in the atmosphere for decades.