NOAA/CMDL Firn Air Measurements of Halogenated Gases Data placed in this directory are NOAA/CMDL measurements of halogenated gases in firn air at South Pole, Antarctica (1995); Tunu, Greenland (1996); and Siple Dome, Antarctica (1997). Analyses of these measurements have been published in the following paper: Butler J. H., Battle M., Bender M., Montzka S. A., Clarke A. D., Saltzman E. S., Sucher C., Severinghaus J., and Elkins J. W. (1999) A record of atmospheric halocarbon concentrations during the twentieth century from polar firn air. Nature 399, 749-755. The data in this directory are organized by analytical instrument. OTTO is a three-channel, isothermal, packed column gas chromatograph with electron-capture detection (GC/ECD) that injects air samples directly. LEAPS is also a GC/ECD, but with a capillary column, temperature programmed oven, and injection of cryotrapped air. GCMS refers to the gas chromatographs with mass spectrometric detection, which also have capillary columns, temperature programming, and injection of cryotrapped air. Because contamination of the extremely low level samples is a concern in the sampling and analysis of firn air, means of paired flasks or even means of measurements on single flasks do not always tell the whole story. Consequently, the data presented here include individual measurements, flask averages, and averages for each depth sampled. Glass and steel flasks were used for many analyses and the data have been included for both whenever this was possible. Limited amounts of air precluded analysis of the glass flasks by GCMS. Anyone is welcome to download these data and work with them. If using the data in a presentation or a publication, the source of these data should be acknowledged and appropriate references cited. We prefer that you contact Dr. James Butler (jbutler@cmdl.noaa.gov, 303-497-6898), Dr. Stephen Montzka (smontzka@cmdl.noaa.gov, 303-497-6657), or Dr. James Elkins (jelkins@cmdl.noaa.gov, 303-497-6224) before using these data in any publication. Other firn air data will be made available at this ftp site as they are published. N2O, CO2, and CH4 data from these sites, and in partial support of an earlier publication, will appear on this site soon. That publication is Battle M., Bender M., Sowers T., Tans P., Butler J., Elkins J., Ellis J., Conway T., Zhang N., Lang P., and Clarke A. (1996) Histories of atmospheric gases from the firn at South Pole. Nature 383(6597), 231-235.