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Earth System Research Laboratory - Global Monitoring Division

The Earth System Research Laboratory - Global Monitoring Division (ESRL), formerly the Climate Monitoring and Diagnostics Laboratory (CMDL), is part of NOAA's Office of Oceanic and Atmospheric Research (OAR). The ESRL traces its roots in ozone monitoring back to the U.S. Weather Bureau and its measurements of total column ozone as part of the International Geophysical Year (IGY), 1957. W.D. Komhyr established the U.S. Dobson network in its current form with well-characterized and calibrated instruments and standardized operating procedures in the early 1960s.

The NOAA/ESRL Cooperative Dobson network of 16 stations (including five sites within the continental U.S., one in Hawaii, and another at the South Pole with data records of nearly forty years in length) observes the total atmospheric ozone column using ground-based Dobson spectrophotometers. The instruments are regularly calibrated against World Standard Dobson No. 83 maintained by ESRL and provide a very stable observational record well suited for determining long-term changes in ozone. The World Standard is calibrated annually at Mauna Loa Observatory. Data from Dobson No. 83 at Mauna Loa are also used for validating satellite column ozone measurements.

A network of eight ozonesonde sites makes weekly ozone vertical profile observations from the surface to about 35 km using electrochemical concentration cell (ECC) ozonesondes. Three of these sites, Boulder, Colorado; 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 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 stratosphere ozone layer to depletion from human-produced chlorine and bromine compounds, the ozone profile measurements should provide sensitive indicators of ozone recovery as the ozone destroying compounds decrease.

Along with the total column and profile measurements of ozone, measurements of the human produced chlorine and bromine compounds responsible for ozone depletion have been made by ESRL since 1977. 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 that are the source of chlorine and bromine in the stratosphere. These data show that effective equivalent chlorine (this accounts for bromine as well as chlorine) peaked in the lower atmosphere in 1994 and has since begun to slowly decline.


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