The size of the hole in the ozone layer over the Antarctic is the largest ever seen, U.S. scientists reported.

The average area of the hole was more than 17.4 million square kilometres between Sept. 21 and 30, researchers at NASA and the U.S. National Oceanic and Atmospheric Administration (NOAA) said.

Under normal atmospheric conditions, the hole would be about the size of North America, or between 14 million and 15 million square kilometres.

The ozone layer blocks harmful ultraviolet light produced by the sun from reaching the Earth’s surface. The hole is created by the release of chlorine and bromine gas-related pollutants produced through human activity, which react with ozone.

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