In the ALE/GAGE/AGAGE global network program, continuous high frequency gas chromatographic measurements of two biogenic/anthropogenic gases (methane, CH4; nitrous oxide, N2O) and eight anthropogenic gases (chlorofluorocarbons CFCl3, CF2Cl2, and CF2ClCFCl2; methyl chloroform, CH3CCl3; carbon tetrachloride, CCl4; chloroform, CHCl3; hydrofluorocarbon-134a, CH2FCF3; ... hydrofluorocarbons 141b and 142b, CH3CCl2F and CH3CClF2; methyl chloride and methyl bromide) are carried out at 5 globally distributed sites for over 20 years. Data are currently available for all of the species, although chloroform data are only available for recent years. Additional important species have been added at select sites during the course of the program. These include: hydrogen (H2), carbon monoxide (CO), methyl chloride (CH3Cl), methyl bromide (CH3Br), HFC-134a, HFC-152a, HCFC-141b, HCFC-142b, HCFC-22, Halons 1211 and 1301, sulfur hexafluoride (SF6), methylene chloride (CH2C12), trichloroethylene (C2HC13), and tetrachloroethylene (C2C14). The last 3 short-lived gases arise from solvents; AGAGE is attempting to assess their source terms, trends, and seasonal influences that are related to their destruction by the hydroxyl (OH) radical.
The program is divided into three parts, reflecting changes in instrumentation. The ALE program, begun in 1978, used a Hewlett Packard HP5840 gas chromatograph; the GAGE program, begun in 1983, uses an HP5880 gas chromatograph. The recently initiated Advanced GAGE (AGAGE) uses a new fully automated system designed by the Scripps Institution of Oceanography containing custom-designed sample module and an HP5890 and Carle gas chromatographic instruments.
The GAGE and AGAGE data were updated and revised through September 2004. The GAGE data were re-calibrated to bring the GAGE data up to the same calibration standards as the AGAGE data. The old HP5880 instruments used in GAGE have been turned off and with the possible exception of Samoa, there will be no more new GAGE data. Revisions are still possible if calibration standards are recalculated.
Data is currently collected at monitoring sites at Cape Grim, Tasmania; Port Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and, Cape Trinidad, California. A site at Adrigole, Ireland was replaced by Mace Head. The Cape Meares, Oregon site was replaced by Trinidad Head, California. During ALE, data was collected 4 times per day and during GAGE, 12 times per day.
Data from all three experiments are posted. AGAGE data through March 2006 are now available for all five existing sites (although monthly data for Trinidad Head, California, USA, are only summarized through October 2004). Individual measurements (generally made 4 times daily at each site for ALE, 12 times daily at each site for GAGE, and more than 30 times daily at each site for AGAGE) and monthly summary averages are provided for each site. All ALE and GAGE data have been recalculated according to the current AGAGE calibration standards, thus creating a unified ALE/GAGE/AGAGE data set. All ALE/GAGE/AGAGE data previously reported based on the Scripps Institution of Oceanography (SIO)-1998 calibration scale are now recalibrated to the SIO-2005 scale; more information about instrumentation and calibration for ALE, GAGE and AGAGE is given by Prinn et al. (2000).
The directories 'gage', 'Agage', and 'ale' contains two subdirectories: 'complete' representing all individual measurements (4 times daily at each site for ALE and 12 times daily for each site for GAGE and AGAGE); and 'monthly', representing monthly summary averages of individual measurements. Data are in units of dry air mole fractions multiplied by 10**12 for all halocarbons and dry air mole fractions multiplied by 10**9 for nitrous oxide and methane.
Please see the 'readme' file in the 'ale', 'gage', or 'Agage' directories for a list of references for primary standards used for the ALE/GAGE/AGAGE datasets.
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