The 2023 Antarctic ozone hole reached its maximum size on September 21, according to annual satellite and balloon measurements by NASA and NOAA. At 26 million square kilometers, the crater is the 16th largest since 1979.
During the peak of the ozone depletion season, from September 7 to October 13, this year’s hole averaged 23.1 million square kilometers, about the size of North America.
“This is a modest ozone hole,” said Paul Newman, head of NASA’s ozone research team and chief scientist for Earth sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Decreasing levels of man-made chlorine compounds, with the help of an active stratospheric climate in Antarctica, slightly improved ozone levels this year.”
The ozone layer acts as the Earth’s natural sunscreen because this part of the stratosphere protects our planet from the harmful ultraviolet radiation of the Sun. The thinning of the ozone layer means less protection from ultraviolet rays, which can cause sunburn, cataracts, and skin cancer in humans.
Every September, the ozone layer thins to form an “ozone hole” over the Antarctic continent. The hole is not completely free of ozone; scientists use the term “ozone hole” as a metaphor for the area where ozone concentrations in Antarctica fall well below the historical threshold of 220 Dobson units. Scientists first reported ozone depletion in 1985 and have tracked ozone levels in Antarctica every year since 1979.
Antarctic ozone depletion occurs when man-made chemicals containing chlorine and bromine first rise into the stratosphere. These chemicals break down and release chlorine and bromine to start chemical reactions that destroy ozone molecules. Ozone-depleting chemicals, including chlorofluorocarbons (CFCs), were once widely used in aerosols, foams, air conditioners, fire extinguishers, and refrigerators. CFCs, the main gases that deplete the ozone layer, have a lifetime in the atmosphere of 50 to over 100 years.
The 1987 Montreal Protocol and its subsequent amendments banned the production of CFCs and other ozone-depleting chemicals worldwide by 2010. The resulting reduction in emissions led to a reduction in chemicals that harm the atmospheric ozone and signs of stratospheric ozone recovery.
NASA and NOAA researchers monitor the ozone layer over the poles and around the world using instruments aboard NASA’s Aura, NOAA-NASA Suomi NPP, and NOAA-20 satellites. Aura’s microwave probe also calculates ozone-depleting chlorine levels.
The scientists also tracked the average rate of decline by measuring the concentration of ozone inside the hole. At NOAA’s South Pole Baseline Atmospheric Observatory, scientists measure the thickness of the layer by launching weather balloons carrying ozonesondes, in addition to making measurements on the ground using a Dobson spectrophotometer.
NOAA measurements showed a low value of 111 Dobson units (DU) over the South Pole on October 3. NASA measurements, averaging over a wider area, recorded a minimum of 99 DU on the same date. In 1979, the average concentration in Antarctica was 225 DU.
“Although total column ozone is never zero, in most years, we usually see zero ozone at some altitude within the stratosphere above the South Pole,” said NOAA research chemist Bryan Johnson, the project leader of the Ozonesondes group from the Global Monitoring Laboratory. “This year, we saw about a 95% reduction, whereas we usually see almost a 100% loss of ozone within the stratosphere.”
The Hunga Tonga-Hunga Ha’apai volcano, which erupted violently in January 2022 and spewed a large amount of water vapor into the stratosphere, may have contributed to this year’s ozone depletion. That water vapor likely increased the ozone depletion reaction in Antarctica earlier in the season.
“If Hunga Tonga hadn’t exploded, the ozone hole might have been smaller this year,” Newman said. “We know that the explosion reached the Antarctic stratosphere, but we cannot yet measure its effect on the ozone hole.”