The largest ozone hole ever documented above the North Pole has closed almost as quickly as it formed. The hole formed earlier this year and reached its maximum size in March some 11 miles above the surface of the Earth. It was the largest ozone hole ever documented over the Arctic, beating the previous record holder, which was observed during the 2011 winter. Researchers with Copernicus' Atmospheric Monitoring Service believed the hole was caused by an unusually strong polar vortex, which explained its relatively sudden growth, according to a report in CNN. The polar vortex is a high altitude current that circulates in an irregular ring-like pattern around the Arctic and helps keep cold air trapped above the pole. When temperatures drop to a low enough point, polar stratospheric clouds (PCS) can form, which can in turn activate ozone-depleting chemicals like chlorine in the atmosphere. On average, temperatures above the Arctic aren't quite as cold as those above Antarctica, which makes the seasonal appearance of ozone holes in the north rare, while it is a yearly phenomenon in the south. Ozone helps filter ultaviolet light from the atmosphere, and when holes appear it means more harmful solar radiation is penetrating the atmosphere and reaching the Earth's surface. It's been driven by an unusually strong and long-lived polar vortex, and isn't related to air quality changes.
