Satellites observed the largest ozone hole over
Antarctica in 2006. Purple and blue represent areas of low ozone concentrations
in the atmosphere; yellow and red are areas of higher
concentrations.
Image Credit:
NASA
NASA
research shows Earth's atmosphere contains an unexpectedly large amount of an
ozone-depleting compound from an unknown source decades after the compound was
banned worldwide.
Carbon tetrachloride (CCl4), which was once used in applications such as dry
cleaning and as a fire-extinguishing agent, was regulated in 1987 under the
Montreal Protocol along with other chlorofluorocarbons that destroy ozone and
contribute to the ozone hole over Antarctica. Parties to the Montreal Protocol
reported zero new CCl4 emissions between 2007-2012.
However, the new research shows worldwide emissions of CCl4 average 39
kilotons per year, approximately 30 percent of peak emissions prior to the
international treaty going into effect.
"We are not supposed to be seeing this at all," said Qing Liang, an
atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt,
Maryland, and lead author of the study. "It is now apparent there are either
unidentified industrial leakages, large emissions from contaminated sites, or
unknown CCl4 sources."
NASA video discusses new research that shows
Earth's atmosphere contains an unexpectedly large amount of an ozone-depleting
compound from an unknown source decades after the compound was banned
worldwide.
As
of 2008, CCl4 accounted for about 11 percent of chlorine available for ozone
depletion, which is not enough to alter the decreasing trend of ozone-depleting
substances. Still, scientists and regulators want to know the source of the
unexplained emissions.
For almost a decade, scientists have debated why the observed levels of CCl4
in the atmosphere have declined slower than expectations, which are based on
what is known about how the compound is destroyed by solar radiation and other
natural processes.
"Is there a physical CCl4 loss process we don't understand, or are there
emission sources that go unreported or are not identified?" Liang said.
With zero CCl4 emissions reported between 2007-2012, atmospheric
concentrations of the compound should have declined at an expected rate of 4
percent per year. Observations from the ground showed atmospheric concentrations
were only declining by 1 percent per year.
To investigate the discrepancy, Liang and colleagues used NASA's 3-D GEOS
Chemistry Climate Model and data from global networks of ground-based
observations. The CCl4 measurements used in the study were made by scientists at
the National Oceanic and Atmospheric Administration's (NOAA's) Earth System
Research Laboratory and NOAA's Cooperative Institute for Research in
Environmental Sciences at the University of Colorado, Boulder.
Model simulations of global atmospheric chemistry and the losses of CCl4 due
to interactions with soil and the oceans pointed to an unidentified ongoing
current source of CCl4. The results produced the first quantitative estimate of
average global CCl4 emissions from 2000-2012.
In addition to unexplained sources of CCl4, the model results showed the
chemical stays in the atmosphere 40 percent longer than previously thought. The
research was published online in the Aug. 18 issue of Geophysical Research
Letters.
"People believe the emissions of ozone-depleting substances have stopped
because of the Montreal Protocol," said Paul Newman, chief scientist for
atmospheres at NASA's Goddard Space Flight Center, and a co-author of the study.
"Unfortunately, there is still a major source of CCl4 out in the world."
NASA monitors Earth's vital signs from land, air and space with a fleet of
satellites and ambitious airborne and ground-based observation campaigns. NASA
develops new ways to observe and study Earth's interconnected natural systems
with long-term data records and computer analysis tools to better see how our
planet is changing. The agency shares this unique knowledge with the global
community and works with institutions in the United States and around the world
that contribute to understanding and protecting our home planet.
For more information about NASA's Earth science activities in 2014,
visit:
For information on the Antarctic ozone hole, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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