WASHINGTON (AP) — The Antarctic ozone hole is back to an average size, shrinking about 16 percent from last year's record high, NASA said Friday. But it's still the size of North America.

The ozone hole in mid-September reached a maximum size of 9.7 million square miles, down from its peak of 11.5 million square miles last year, said NASA atmospheric scientist Paul Newman.

Human-produced gases, containing chlorine and bromine, damage the Earth's protective ozone layer, forming a hole over the South Pole and into the Southern Hemisphere. Because the ozone layer protects life on Earth by blocking ultraviolet rays, countries across the world 20 years ago agreed to ban many compounds such as spray-can propellants.

The ozone hole was first discovered in 1985, is not natural and at the current rate should be closed up by 2070, Newman said.