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NASA scientists report the ozone hole over Antarctica 

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has reached an annual maximum size of 10.9 million square miles

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on October 2nd, 2015. The Antarctic ozone hole 

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is caused by manmade ozone-depleting chemicals and has been a feature of 

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the atmosphere for more than 3 decades. But measurements by NASA's AURA 

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satellite show this is one of the largest and latest forming maximum ozone holes 

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seen in recent years. Scientists say this is due to two

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factors: elevated levels of ozone-depleting chlorine chemicals

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in the atmosphere and a particularly strong polar vortex.

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The polar vortex is a jet of cold air that circles Antarctica. It develops when the 

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sun sets over the South Pole for the entire winter. The cold temperatures 

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within the vortex create polar stratospheric clouds.

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When these clouds come into contact with chlorine-containing chemicals, it can lead to 

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ozone depletion. The mix of the unusually strong vortex along 

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with the elevated levels of ozone-depleting chlorine caused this year's 

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ozone hole to be both unseasonable late and large.

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Despite it's size, scientists expect the hole will disappear by 2070

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as levels of ozone-depleting chemicals in the atmosphere decline.