The 2021 Antarctic ozone hole reached its maximum area on Oct. 7 and ranks 13th-largest since 1979, scientists from NASA and NOAA reported today. This year’s ozone hole developed similarly to last year's: A colder than usual Southern Hemisphere winter led to a deep and larger-than-average ozone hole that will likely persist into November or early December.
“This is a large ozone hole because of the colder than
average 2021 stratospheric conditions, and without a Montreal Protocol, it
would have been much larger,” said Paul Newman, chief scientist for Earth
sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The 2021 Antarctic ozone hole reached its maximum area on Oct. 7 and ranks 13th largest since 1979. Credits: NASA Ozone Watch
What we call the “ozone hole” is a thinning of the ozone layer in the stratosphere (an upper layer of Earth’s atmosphere) above
Antarctica that begins every September. Chemically active forms of chlorine and
bromine derived from human-produced compounds are released during reactions on
high-altitude polar clouds. The reactive chlorine and bromine then initiate
ozone-destroying reactions as the sun rises in the Antarctic at the end of
winter.
A scientist launches a weather balloon carrying an ozonesonde from South Pole Station in March of 2021. Credits: NOAA Global Monitoring Laboratory
NASA and NOAA researchers detect and
measure the growth and break up of the ozone hole with satellite instruments
aboard Aura, Suomi-NPP and NOAA-20.
This year, NASA satellite observations determined the
ozone hole reached a maximum of 9.6 million square miles (24.8 million square
kilometers) – roughly the size of North America – before beginning to shrink in
mid-October. Colder than average temperatures and strong winds in
the stratosphere circling Antarctica contributed to
its size.
NOAA scientists at the South Pole Station, one of a
world-wide ozone monitoring network, record the ozone layer's thickness by
releasing weather balloons carrying ozone-measuring instruments called ozonesondes that measure the varying ozone concentrations as the balloon rises
into the stratosphere.
When the polar sun rises, NOAA scientists also make
measurements with a Dobson
Spectrophotometer, an optical instrument that records the
total amount of ozone between the surface and the edge of space known as the
total column ozone value. This year, scientists recorded the lowest
total-column ozone value of 102 Dobson Units on
Oct. 7, the 8th-lowest since 1986. At altitudes between 8 and 13 miles (14 to
21 kilometers) ozone was nearly completely absent during the ozone hole’s
maximum.
While the 2021 Antarctic ozone hole is larger than
average, it’s substantially smaller than ozone holes in the late 1990s and
early 2000s.
The ozone hole is recovering due to the Montreal Protocol and subsequent amendments banning the
release of harmful ozone-depleting chemicals called chlorofluorocarbons, or
CFCs. If atmospheric chlorine levels from CFCs were as high today as they were
in the early 2000s, this year’s ozone hole would have been larger by about 1.5
million square miles (about four million square kilometers) under the same
weather conditions.
Many ozone holes in the
1990s and early 2000s were significantly larger than the 2021 ozone hole in
terms of average ozone hole area from early September to mid-October. Credits:
NASA’s Earth Observatory/Joshua Stevens
By Sofie Bates
NASA's Earth Science News Team
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