Ozone hole

Houston Chronicle Sunday - - WORLD -

The hole in Earth’s pro­tec­tive strato­spheric ozone layer above Antarc­tica was the small­est since 1988 at the time of year it typ­i­cally reaches its great­est ex­panse.

The hole reached its peak on Sept. 11, cov­er­ing about 7.6 mil­lion square miles be­fore be­gin­ning its an­nual re­treat. The av­er­age peak since 1991 has been about 10 mil­lion square miles.

Re­searchers say the lim­ited size was mainly due to ab­nor­mally un­sta­ble and warmer air swirling high above Antarc­tica in the south­ern po­lar vor­tex.

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