The Ozone Layer
Ozone is a gas that occurs naturally in our atmosphere. Most of it is
concentrated in the ozone
layer, a
region located in the stratosphere several miles above the surface of
the Earth. Although ozone represents only a small fraction of the gas
present in the atmosphere, it plays a vital role by shielding humans
and other life from harmful ultraviolet light from the Sun. Human activities
in the last several decades have produced chemicals, such as chlorofluorocarbons
(CFCs), which have been released into the atmosphere and have contributed
to the depletion of
this important protective layer. When scientists realized the destructive
effect these chemicals could have on the ozone layer, international
agreements were put in place to limit such emissions. As a result, it is expected
that the ozone layer will recover in the coming decades.
Ozone is also a greenhouse
gas in
the upper atmosphere and, therefore, plays a role in Earth's climate.
The increases in primary greenhouse gases, such as carbon dioxide,
may affect how the ozone layer recovers in coming years. Understanding
precisely how ozone abundances will change in a future with diminished
chlorofluorocarbon emissions and increased emissions of greenhouse gases
remains an important challenge for atmospheric scientists in NOAA and
other research centers.
Ozone Research
NOAA Research has, for many years, played a vital
role in studying the ozone
layer. For
instance, at the Chemical Sciences
Division of ESRL,
researchers are conducting laboratory and field experiments and designing
computer models to study this issue. One of the primary missions of
ESRL's Global Monitoring Division is
to observe and understand the ozone layer through accurate, long-term
measurements of ozone, chlorofluorocarbons, greenhouse gases, and solar
radiation.
Taking Observations
NOAA researchers build and deploy instruments all
over the world to measure ozone, as well as the trace gases and aerosol
particles that affect its abundance. They also participate in many
field experiments to study and document the processes that control
atmospheric ozone. Research scientists take ozone
measurements using
instruments located on the ground and onboard aircraft, balloons, and
satellites. The data
from these instruments provide
precise measurements that can be used to detect small regional ozone
changes over long periods of time, provide global maps of ozone amounts
and examine local ozone distributions.
Ozone Depletion
Antarctica
Ozone depletion occurs in many places in the Earth's ozone
layer, most severely in the polar regions. NOAA scientists have traveled
to Antarctica to study the ozone
hole that
has been occurring there since the late 1970s. In 1986, soon after the
reported discovery of the ozone hole, Aeronomy Lab (now ESRL) scientist
Dr. Susan Solomon led a team of 16 scientists, the National
Ozone Expedition (NOZE I), to
Antarctica. The scientists took measurements of various trace gases and
physical properties of the atmosphere. The data, along with additional
findings from the NOZE II mission the following year, showed conclusively
that human-produced trace gases that contain chlorine and bromine were
causing the ozone hole. The Global Monitoring Division of ESRL has monitored
the yearly Antarctic ozone hole since 1986 by launching balloon-borne ozonesondes,
from the South Pole station and measuring total column ozone from a ground
based Dobson spectrophotometer since
1963.
This unique record from the South Pole station clearly
shows the annual development of the springtime Antarctic ozone hole over
the past two decades. Ozone depletion at the South Pole can also be viewed
from another perspective through the images created from data collected
by the NASA TOMS satellite,
and the NOAA
SBUV-2 instruments
aboard NOAA satellites. These various ozone measurements provide an important
record of the status of the ozone hole. Continued surveillance is necessary
in order to verify the expected recovery of the ozone layer.
Arctic Ozone
Significant depletion also occurs in the Arctic
ozone layer during
the late winter and spring period (January - April). However, the maximum
depletion is generally less severe than that observed in the Antarctic,
with no large and recurrent ozone hole taking place in the Arctic.
Since the 1980's, scientists at ESRL
have been participants in field, theoretical, and laboratory research
to demonstrate some of the key processes that contribute to the observed
difference between the depletion of ozone in the Arctic and Antarctic.
For example, the POLARIS
mission in
1997, was designed to study ozone photochemistry in the Arctic during
the summertime at middle and high latitudes. And later, the SAGE
III Ozone Loss and Validation Experiment (SOLVE) campaign
was designed to examine the processes controlling ozone levels at mid-
to high latitudes in the Arctic during the winter. The mission also acquired
correlative data needed to validate the Stratospheric Aerosol and Gas
Experiment (SAGE) III satellite measurements that are used to quantify
high-latitude ozone loss. Both these experiments took measurements using
the NASA DC-8 and ER-2 aircraft, as well as balloon platforms and ground-based
instruments
Atmospheric Models
Another NOAA lab involved in studying stratospheric ozone
depletion is the Geophysical Fluid
Dynamics Laboratory (GFDL) in
Princeton, N.J. GFDL seeks to understand and predict the Earth's climate
and weather, including the impact of human activities. Specifically,
GFDL conducts leading-edge research (i.e., atmospheric chemistry modeling)
on many topics of great practical value, including stratospheric
ozone depletion. For
example, the GFDL group developed a 3-D atmospheric model tailored to
study the interaction of chemistry, dynamics, and radiation in the stratosphere.
Their extensive calculations were necessary for evaluating the simpler
models used in the policy assessment studies, as well as for understanding
the climatic impact of the Antarctic ozone hole.
Ozone-Depleting Substances
Certain industrial processes and consumer products
result in the atmospheric emission of ozone-depleting gases. These
gases contain chlorine and bromine atoms, which are known to be harmful
to the ozone layer. Important examples are the CFCs and
hydrochlorofluorocarbons
(HCFCs),
human-produced gases once used in almost all refrigeration and air conditioning
systems. These gases eventually reach the stratosphere, where they are
broken apart to release ozone-depleting chlorine atoms. Other examples
are the halons,which are used in fire
extinguishers and which contain ozone-depleting bromine atoms.
Methyl
bromide, is
another important area of research for NOAA scientists. Primarily used
as an agricultural fumigant, it is also a significant source of bromine
to the atmosphere. Although some ozone-depleting gases also are emitted
from natural sources, emissions from human activities exceed those from
natural sources.
NOAA researchers regularly measure
ozone depleting gases in the lower and upper atmosphere and attempt to account for observed
changes. As a result of international regulations, ozone-depleting gases
are being replaced in human activities with "ozone-friendly" gases
that have much reduced potential to deplete ozone. NOAA researchers are
also measuring
these "substitute" gases as
they accumulate in the atmosphere. Observing changes in both old and
new gases emitted into the atmosphere allows researchers to improve our
understanding of the fate of these gases after release and thereby improve
our ability to predict future ozone changes.
Winter Ozone Summaries
The full range of ground-based and satellite-based
observations from several NOAA offices are collected together and used
to describe the past Arctic or Antarctic winter in the Climate Prediction
Center's Winter Ozone Summaries. The contributors include the National
Weather Service's Climate Prediction Center (CPC), NOAA
Research and
the National Environmental Satellite,
Data, Information Services (NESDIS).
By monitoring and researching stratospheric ozone, as well as the chemical
compounds and atmospheric conditions that affect its concentration, NOAA has
contributed vital information toward protecting the Earth's stratospheric ozone
layer. Perhaps most notable is NOAA's instrumental role in providing ozone
data and analysis for the United
Nations Environmental Programme and World
Meteorological Organization.
Communicating Information on Ozone depletion
The world's population is a stakeholder in decisions that
limit the emissions of ozone-depleting gases. In 1987, the international
community put in place a treaty known as the Montreal
Protocol on Substances that Deplete the Ozone Layer .
Since that initial treaty was ratified, periodic assessments and updates
have been conducted. The Protocol success has derived in part from these
scientific updates on the science and observation of ozone depletion
made over the past 15+ years. NOAA researchers from several laboratories
have participated in all of these scientific updates and have also been
active in preparing outreach documents to communicate the science
of ozone depletion to the public.