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NOAA MONITORS STRATOSPHERIC OZONE, AS WELL AS THE CHEMICAL COMPOUNDS AND ATMOSPHERIC CONDITIONS THAT AFFECT ITS CONCENTRATION

Image of Antarctic ozone hole with NOAA logo superimposed on top of it. November 15, 2002 — In the stratosphere, the region of the Earth's atmosphere from six to 30 miles (10 to 50 km) above the surface, ozone plays a vital role in absorbing harmful ultraviolet radiation from the sun. Over the last 20 years, however, ozone concentrations have been depleted by man-made gases released into the atmosphere (e.g., chlorine and bromine containing compounds such as chlorofluorocarbons, carbon tetrachloride, methyl chloroform and halons). These "ozone depleting" compounds — in the presence of certain meteorological conditions — lead to the destruction of atmospheric ozone and ultimately the Antarctic Ozone Hole. The Antarctic ozone hole is defined as the region with total ozone below 220 Dobson units — while normal ozone readings are around 275 Dobson units (a Dobson unit is a unit of measurement that describes the thickness of the ozone layer in a column directly above the location being measured).

An international agreement known as the Montreal Protocol on Substances That Deplete the Ozone Layer was reached in 1987. Through that agreement (and subsequent amendments and adjustments) many nations of the world have carried out policies to reduce and then phase out their use of ozone-depleting chemicals. The Montreal Protocol also called for the international scientific community to periodically update governments on the latest scientific findings related to the ozone layer. Specifically, every three to four years, under the auspices of the World Meteorological Organization and the United Nations Environment Programme, the world's leading experts produce a written document presenting the consensus view of the scientific "big picture." These periodic "state-of-the-science" assessments have guided policymakers as they strengthened the original provisions of the Montreal Protocol. Together with colleagues from around the nation and world, NOAA scientists have played prominent roles in coordinating, preparing, and reviewing the scientific assessments. In addition, the director of the Aeronomy Lab, Daniel L. Albritton, serves as scientific consultant to the United Nations Environment Programme during the international Montreal Protocol Meetings. The latest assessment was conducted in 1998 (previous reports were in 1985, 1989, 1991, and 1994). The 2002 assessment is currently in preparation and is expected to be published in early 2003.

NOAA uses satellite, airborne and ground-based systems to continuously monitor stratospheric ozone, as well as the chemical compounds and atmospheric conditions that affect its concentration (i.e., sunlight and cold temperatures, such as those found in association with polar stratospheric clouds and a strong polar vortex (or circumpolar winds) — conditions most often associated with the Antarctic spring). The following three NOAA offices are actively involved in stratospheric ozone research and monitoring activities that have enhanced the understanding of stratospheric ozone depletion and the processes that affect its concentration: The NOAA Office of Oceanic and Atmospheric Research (NOAA Research), National Weather Service, and National Environmental Satellite, Data and Information Service (Click here for Summary of NOAA Stratospheric Ozone Activities by Office).

1) NOAA OFFICE OF OCEANIC AND ATMOSPHERIC RESEARCH
Several offices within NOAA Research are actively engaged in ozone work, the NOAA Climate Monitoring & Diagnostics Laboratory, Aeronomy Laboratory and Geophysical Fluid Dynamics Laboratory. Other NOAA Research offices that also participate in ozone research include the NOAA Air Resources Laboratory and Atlantic Oceanographic and Meteorological Laboratory.

A) NOAA Climate Monitoring & Diagnostics Laboratory
The NOAA CMDL (located in Boulder, Colo.) monitors both stratospheric ozone levels and the chemical components that affect its concentration.

Total Ozone Column Measurements: Total ozone column observations can be defined as the total amount of ozone in a column from the surface of the Earth to the top of the atmosphere. Spectrophotometers, developed in the 1920s, have been used to measure total ozone columns and have allowed researchers to establish one of the longest geophysical measurement series in existence.
CMDL can trace its roots in ozone monitoring back to the U.S. Weather Bureau, when it was first charged with measuring total column ozone levels as part of the International Geophysical Year in 1957. Specifically, a NOAA scientist established the U.S. Dobson network in its current form with well-characterized and calibrated instruments and standardized operating procedures was established in the early 1960s. Today, CMDL’s cooperative Dobson network consists of 16 stations (including five sites within the continental United States, one in Hawaii, and another at the South Pole — with data records of nearly forty years in length), all of which continue to use ground-based Dobson spectrophotometers to observe total ozone column levels. The instruments are regularly calibrated against World Standard Dobson No. 83 (located at Mauna Loa, Hawaii) and provide a very stable observational record well suited for determining long-term changes in ozone and for validating satellite column ozone measurements. CMDL is the World Dobson Ozone Calibration Centre under the Global Atmosphere Watch, and is responsible for the calibration of more than 100 instruments worldwide.

Total ozone column measurements are particularly useful in that they allow researchers to track changes — both decreases and increases — in ozone levels at particular altitudes (and locations) above the Earth. It is just as important to track all changes in ozone levels, since increasing ozone levels will serve as the primary indicator that the stratospheric ozone level is recovering (thus verifying that all relevant processes in ozone destruction have been identified and that appropriate measures have been taken to assure the ozone layer's health).

Vertical Ozone Profiles: CMDL maintains a network of eight ozonesonde sites, where weekly ozone vertical profile observations are made from the Earth’s surface to about 35 km using electrochemical concentration cell (ECC) ozonesondes. Three of these sites — Boulder, Colo., Hilo, Hawaii, and South Pole, Antarctica — have records of at least 15 years in length covering a significant portion of the period that stratospheric ozone has been declining. The unique record from the South Pole station clearly shows the annual development of the springtime Antarctic "ozone hole," along with deepening of the "ozone hole" over the past two decades. Because of the sensitivity of the Antarctic stratospheric ozone layer to depletion induced by man-made ozone depleting compounds, the ozone profile measurements should provide sensitive indicators of ozone recovery as man-made ozone depleting compounds decrease.

Chlorine and Bromine Containing (Man-made Ozone Depleting) Compounds: In addition to ozone total column and profile measurements, CMDL has also been researching and monitoring man-made chlorine and bromine compounds responsible for ozone depletion since 1977. Specifically, weekly flask grab samples and continuous in-situ analyzer data from eight stations (ranging from the high Arctic to the South Pole) provide information on the gases known to be the primary sources of chlorine and bromine in the stratosphere. This research has already shown that chlorine and bromine levels peaked in the lower atmosphere in 1994 and have since then begun to slowly decline, as expected under the Montreal Protocol on Substances That Deplete the Ozone Layer.

B) NOAA Aeronomy Laboratory
The NOAA Aeronomy Laboratory conducts scientific research on the chemistry and dynamics of the Earth's stratosphere, with emphasis on processes affecting the stratospheric ozone layer. Specifically, Aeronomy Laboratory scientists made many key contributions to the current understanding regarding connections between human activities and the health of the stratospheric ozone layer. One prominent example is the work of an Aeronomy Laboratory scientist whose work ultimately determined the cause of the Antarctic ozone hole. The Aeronomy Laboratory's research findings have and continue to provide the sound scientific information both industry and government officials need to make informed policy decisions related to stratospheric ozone protection (as well as a number of other related issues, such as air quality improvement and climate change issues). For example, Aeronomy Laboratory scientists (in collaboration with other NOAA scientists) have played leading roles in developing "state-of-the-science" assessment reports for use by national and international decision makers. More examples of AL's research accomplishments related to stratospheric ozone can be found on their Web site.

C) NOAA Geophysical Fluid Dynamics Laboratory
The NOAA 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 modelling) 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.

2) NOAA NATIONAL WEATHER SERVICE
Within the NOAA NWS, the NOAA Climate Prediction Center is the only office which works on ozone issues.

A) NOAA Climate Prediction Center
The NOAA Climate Prediction Center (part of the National Weather Service) has been involved in analyzing total ozone and ozone profile information since the early 1970s. Before 1985, total and profile ozone data from NASA satellites (NIMBUS-4 and NIMBUS-7) were analyzed and monitored. Then in 1985, NOAA-9 was launched carrying the Solar Backscatter Ultraviolet/2 (SBUV/2) ozone monitoring instrument. From that time on, CPC has continued to analyze and monitor the ozone layer using data from this and subsequent SBUV/2 instruments on the NOAA-11, NOAA-14, NOAA-16, and the current NOAA-17 Polar-orbiting Operational Environmental Satellites operated by NOAA/NESDIS (See “NESDIS” section below). Since the mid-1980s CPC has been using the SBUV/2 data to monitor the size of the Antarctic ozone hole during the austral spring.

CPC presents many stratosphere related products via the World Wide Web. For example, CPC has monitored heights and temperatures of the stratosphere since the 1960s and now provides these products on the Internet with commentary of how the ozone fields are linked with the thermal and dynamic structure of the stratosphere. CPC has also published a Southern Hemispheric Winter Bulletin every December and a Northern Hemispheric Winter Bulletin every April since 1991. These reports summarize NOAA's observations and explains the status of the ozone layer and the stratospheric temperatures and dynamics in context with the historical record.

CPC continually monitors measured ozone amounts for accuracy by comparing them against data observed via other land or satellite based instruments. Land-based observations include those made by the CMDL Dobson network for total ozone and LIDAR observations for ozone profile information. Satellite-based instruments include observations from the SAGE and MLS.

3) NOAA National Environmental Satellite, Data and Information Service
There are three primary offices within the NOAA National Environmental Satellite, Data and Information Service that work with satellite derived ozone data: The NOAA Office of Satellite Data Processing and Distribution and Office of Research and Applications Division, — both of which work to maintain, understand, characterize, and calibrate satellite instruments and algorithms and retrieve ozone information from their measurements (i.e., SBUV/2 and TOVS ozone products) — and National Climate Data Center, which works primarily with ozone (and other) data management tasks.

A) Office of Satellite Data Processing and Distribution: OSDPD downloads and processes the ozone data from the POES satellites. OSDPD also maintains operational ozone algorithms for SBUV/2 and TOVS atmospheric ozone products, and provide operational ozone estimates on a daily basis (i.e., approximately 1,400 estimates of total columns and vertical profiles of atmospheric ozone are produced daily at OSDPD). These estimates are used by the NWS both in their forecast models and in their UV Index.

B) Office of Research and Applications Division: ORA characterizes and calibrates satellite instruments, develops and improves retrieval algorithms, and reprocesses and validates ozone products for long-term monitoring. ORA monitors both the total and profile ozone data from the SBUV/2 instrument (as well as total ozone data) using the TOVS total ozone algorithm, monitors the instrument's calibrations, and monitors the data with the NOAA CPC for trends (using CMDL data). This office provides a key data resource, both within NOAA and to international ozone assessment community, for assessing the changes in both stratospheric and total column ozone over the last 24 years.

C) National Climatic Data Center: NCDC (located in Asheville, N.C.) stores ozone data and makes it available to the general public. It is the world's largest active archive of weather data from around the globe. NCDC also produces climate reports providing historical perspectives on the Earth's climate, including the weather and climate conditions that influence stratospheric ozone depletion.

NOAA’s Collaborative Ozone Efforts
It is important to emphasize that the above mentioned NOAA offices also work collaboratively on ozone issues to validate ozone data, develop continuous ozone data records and produce winter ozone summaries:

Ozone Data Validation: ORA, NCEP (CPC) and CMDL work together to improve the usefulness and quality of the satellite products. Specifically, ORA validates total ozone products (both operational and reprocessed) by comparing them with CMDL Dobson station measurements. Likewise, NCEP validates ozone profile products by comparing them with CMDL ozonesonde and additional NDSC measurements.
Continuous Ozone Data Records: CPC has worked with NESDIS/OAR to combine several NOAA satellites' SBUV/2 ozone data records into one continuous data record (by removing biases or offsets from each satellite's instrument). The result is a high quality data set, which can be used to determine where and how much the ozone layer has been changing.
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 NESDIS’s Winter Ozone Summaries. The contributors include NWS, OAR and NESDIS researchers.

Most recently, the above mentioned NOAA offices made a significant contribution to understanding what went on this past September when the Antarctic ozone hole was squeezed and divided into two holes (Click here for an animated gif file of this ozone event).

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 World Meteorological Organization’s scientific assessments of ozone depletion (click here for the most recent 2002 report).

Relevant Web Sites
NOAA Ozone Theme Page

Montreal Protocol on Substances That Deplete the Ozone Layer

World Meteorological Organization

United Nations Environment Programme

NOAA's Satellite Theme Page

NOAA Office of Oceanic and Atmospheric Research

NOAA Air Resources Laboratory

Atlantic Oceanographic and Meteorological Laboratory.

NOAA Climate Monitoring & Diagnostics Laboratory

Total Ozone Column Measurements

Vertical Ozone Profiles

CMDL ozonesondes

NOAA Aeronomy Laboratory

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