Ozone measurements reach an all-time low

WASHINGTON (AP) The lowest levels of springtime ozone ever detected over the North Pole have been mapped by instruments on a series of satellites, scientists announced on Tuesday.
Ozone levels in late March and early April over the Arctic were 40 percent lower than the average March measurements made from 1979 to 1982, said Pawan K. Bhartia of NASA’s Goddard Space Flight Center in Greenbelt, Md.
A year ago, measurements detected an ozone hole in the North Atlantic that was about 24 percent less dense than the 1979-82 period, the space agency announced.
Ozone is a natural atmospheric gas that acts as a shield against the ultraviolet radiation of the sun. The gas is eroded away by certain industrial chemicals, principally chlorofluorocarbons that are used as coolants and cleaners.
Under international treaty, the compounds are being phased out of use in most countries of the world, but the effect of chemicals already released into the atmosphere is blamed by most scientists for the current thinning of the ozone layer.
Unshielded ultraviolet radiation can cause skin cancer in humans and can destroy some microscopic sea life that is thought important to the natural food chain.
Although the Arctic ozone has thinned, the loss is not nearly as severe near the North Pole as it is over the South Pole during the Southern Hemisphere spring in September and October.
Chemical reactions that destroy the ozone result from the combination of industrial chemicals, frigid temperatures and sunlight. These conditions usually occur for a brief period as the sun makes its first springtime appearance over the poles after winter’s darkness.
NASA uses instruments aboard U.S. and Japanese satellites to measure the density and distribution of ozone. Measurements also are taken by the National Oceanic and Atmospheric Administration.
One instrument detected an ozone concentration on March 26 of less than one part per million at an altitude of 12.4 miles above the Hudson’s Bay area of northern Canada. Normal ozone concentrations are three to four parts per million.
A weather bureau instrument measured ozone over Barrow, Alaska, on March 17 at less than 300 Dobson units, which is a measure of the gas. The March average for the region has been 413 Dobson units for the last 10 years, according to David Hofmann of the National Oceanic and Atmospheric Administration.
NASA said the area of thinned ozone covered about 2 million square miles of the Arctic region.
Natural atmospheric ozone is found in a thin layer some six to 18 miles above the Earth. There is a global ozone thickness average of 300 Dobson units, which is about an eighth inch, or the thickness of two stacked pennies.
At its worst, the Antarctic ozone hole amounts to about 100 Dobson units, or about one-twenty-fifth of an inch.