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Ozone hole has been slowly shrinking over two decades

The ozone hole is an area in the stratosphere over the North Pole, where the thickness of the ozone layer is reduced for part of each year due to the presence of ozone-depleting substances. Since this layer effectively protects life on Earth from excessive exposure to harmful UV-B radiation from the sun, it is important to keep track of the size of the hole on a regular basis. It is monitored by satellites and scientists from NASA in Maryland, as well as from NOAA, the United States’ National Oceanic and Atmospheric Administration. In the latest report from NASA’s Goddard Space Flight Centre, statistics indicate that this hole has continued on its overall path to becoming smaller during 2022.

Ozone is a colorless gas with the molecular formula O3. It is very active chemically and forms bonds with many other substances. Near the Earth’s surface, those reactions cause rubber to crack, hurt plant life, and damage people’s lung tissues. However, ozone in the stratosphere absorbs UV-B radiation, thus protecting the living things below from its harmful effects. 

Each year, active forms of chlorine and bromine from man-made chemical compounds accumulate and attach to the high-altitude polar clouds during the southern Hemisphere winter. As soon as the sun rises at the start of Antarctica’s spring, the chlorine and bromine undergo chemical reactions that break down ozone. Thus, satellites measure the extent and thickness of the ozone layer during the spring months between July and October each year, in order to assess the extent to which these chemical reactions have negatively affected the ozone layer. 

This year, instruments aboard the Aura, Suomi NPP, and NOAA-20 satellites recorded that the maximum size of the ozone hole (present on Oct. 5, 2022) was 10.2 million square miles (26.4 million square kilometers), which was slightly larger than last year, but smaller than was recorded in 2015. 

In addition, scientists from NOAA used a  Dobson Spectrophotometer, an optical instrument that records the total amount of ozone between Earth’s surface and the edge of space. The global average column ozone is around 300 Dobson units, and this year the lowest value was recorded on Oct. 3, when only 101 Dobson units were present over the South Pole. At that time, ozone was almost completely absent at altitudes between 8 and 13 miles (14 and 21 kilometers) – a pattern very similar to what was recorded last year. 

Some scientists had been concerned about potential stratospheric impacts from the January 2022 eruption of the Hunga Tonga-Hunga Ha’apai volcano in the South Pacific Ocean. The 1991 Mount Pinatubo eruption released substantial amounts of sulfur dioxide that amplified ozone layer depletion. However, no direct impacts from Hunga Tonga have been detected in the Antarctic stratospheric data for the current year.  

The Montreal Protocol, an international treaty signed in 1987, aims to protect the ozone layer by phasing out the use of reactive chlorine and bromine compounds in refrigerants and manufacturing processes. It was ratified by 198 nations and territories and has been in force since 1989. Since then, the atmospheric concentrations of the most important chlorofluorocarbons and related chlorinated hydrocarbons have either leveled off or decreased, and the ozone hole has slowly become smaller. 

“Over time, steady progress is being made, and the hole is getting smaller,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center. “We see some wavering as weather changes and other factors make the numbers wiggle slightly from day to day and week to week. But overall, we see it decreasing through the past two decades. The elimination of ozone-depleting substances through the Montreal Protocol is shrinking the hole.”

Image Credit: NASA Earth Observatory image by Joshua Stevens

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By Alison Bosman, Staff Writer

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