In 2019, the hole that developed in the ozone layer over Antarctica was the smallest on record since 1982, according to the NASA/NOAA press release. In an average spring, the hole expands throughout September and early October to a maximum extent of about 8 million square miles (21 million square kilometers), an area larger than the United States and Canada combined. In 2019, the hole reached 6.3 million square miles (16.4 million square kilometers) on September 8, but then shrank to less than 3.9 million square miles (10 million square kilometers) for the remainder of September and the first half of October.
The ozone hole is a seasonal thin spot that develops in the ozone layer, which, over the South Pole, resides at altitudes from 9-13 miles (14-21 kilometers). It’s observed with both satellites and with weather balloons that NOAA scientists launch at the South Pole. The satellites measure the ozone hole’s area, and the weather balloons measure ozone concentrations as they drift up through a column of the atmosphere. Locations where the total ozone concentration falls below 220 Dobson units are considered part of the ozone hole.
In most years since the hole was discovered, weather balloons rising through the atmospheric column have passed through regions where ozone is completely absent from the middle stratosphere. In 2019, however, they found no segments of the South Pole profile that were completely devoid of ozone.
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Image via NOAA.