The hole in the ozone layer continues to shrink
In past 10–20 years, when spring arrived in the southern hemisphere, the hole in the ozone layer opened over Antarctica. Between September 7 and October 13 of this year, it reached an area of 23.2 million square kilometers, that is, 1.6 million less than in 2021. According to a statement from NASA and NOAA, the data complies with the positive trend of recent years.
The hole in the ozone layer is not a “hole” in the strict sense, that is, it does not present a total absence of gas molecules. What happens is that, in that area, the ozone concentration only oscillates between 130 and 220 Dobson units, whereas, before the massive use of chlorofluorocarbons (CFCs), it was at least between 260 and 320 Dobson units. At lower latitudes, the values usually fluctuate between 300 and 500.
The impoverishment observed in the southern hemisphere intensifies in spring. In winter, the CFC molecules responsible for the hole accumulate over the South Pole and, when the polar night gives way to solar radiation, the radicals begin to destroy the ozone molecules. Only high stratospheric temperatures put an end to the degradation process.
The size of the hole varies depending on the weather conditions, which is why new records have been set in recent years. “However, over time you are seeing steady progress, and the hole is getting smaller and smaller,” says NASA’s Paul Newman. For two decades, atmospheric scientists have observed a trend that could lead to the disappearance of the hole in the long term.
The phenomenon was first described in the 1980s and attributed to the emission of CFCs. Under the Montreal Protocol, which entered into force in 1989, the international community banned the production and use of these long-lived gases, whose atmospheric concentration is now gradually decreasing. However, illegal emissions are frequently detected.
This year, by contrast, experts feared the hole could grow larger because the Hunga Tonga-Hunga Ha’apai eruption in January reached the stratosphere and thus reached the ozone layer. In 1991, Mount Pinatubo released vast amounts of sulfur dioxide, emissions that exacerbated ozone depletion. However, data for the Antarctic stratosphere in 2022 do not reflect a direct influence from Hunga Tunga.