SEE ALSO A IR P OLLUTION ; A STHMA ; CFCs (C HLOROFLUOROCARBONS) ; E LECTRIC P OWER ; H ALON ; M ONTRÉAL P ROTOCOL ; NO x (N ITROGEN O XIDES) ; S MOG ; V EHICULAR P OLLUTION ; U LTRAVIOLET R ADIATION ; VOCs (V OLATILE O RGANIC C OMPOUNDS) .
The Arctic region is typically spared the worst of the ozone destruction because
its vortex normally breaks down several weeks before the sun returns, dissipating
the ice clouds. The larger percentage of land masses in the northern latitudes,
particularly mountains, prevents an excessive build-up of ice clouds. Geography
isn't always enough to dissipate the vortex, however. The North Pole's vortex
was unusually strong and long-lived during the winter of 1992-1993, for example.
When sunlight appeared, it drove down Arctic ozone levels well into March. Because
there is more ozone over the North Pole to begin with, this decline didn't create
a hole. However, it did send ozone-depleted air over populated areas of the
Northern Hemisphere when the vortex broke up.
The loss of ozone over populous regions underscores the importance of following up on the 1987 Montreal Protocol. This agreement, now signed by more than 70 countries, set goals of reducing CFC production by 20% (relative to 1986 levels) by 1993 and by 50% by 1998. These targets have since been strengthened to call for the elimination of the most dangerous CFCs by 1996 and for regulation of other ozone-depleting chemicals. The United States and other nations are well on their way to meeting these goals. In 1993, global CFC production was already down 40% compared to 1986 levels. That's fortunate, since the CFCs already in circulation will continue to pose a threat to the earth's ozone layer for another hundred years. There is good news to this story. The graph below shows the skyrocketing path of CFC-11 from the 1950s until the mid-1990s. Recent measurements have shown a clear decline in CFC-11.