WASHINGTON (AP) — NASA says the ozone hole over Antarctica shrank to its smallest peak since 1988.

The huge hole in Earth’s protective ozone layer reached its maximum in September, and this year NASA says it was 7.6 million square miles wide (19.6 million square kilometers).

NASA scientist Paul Newman says stormy conditions in the upper atmosphere warmed the air and kept chemicals chlorine and bromine from eating ozone.

Newman says this is good news. He says this year’s drop is mostly natural but is on top of a trend of smaller steady improvements likely from the banning of ozone-eating chemicals in a 1987 international treaty.

Ozone is a combination of three oxygen atoms. High in the atmosphere, ozone shields Earth from ultraviolet rays that cause skin cancer, crop damage and other problems.