DB1001

The ALE / GAGE / AGAGE Network

Links to additional sources:

• Advanced Global Atmospheric Gases Experiment (AGAGE) home page
• How halocarbons (CFCs, HFCs, HCFCs, and halons) are named
• CDIAC data base including some of the same compounds, and a tabulation of their uses and atmospheric lifetimes

Investigators

R.G. Prinn; R.F. Weiss; P.J. Fraser; P.G. Simmonds; D.M. Cunnold; S. O'Doherty; P. Salameh; L. Porter; P. Krummel; R.H.J. Wang; B. Miller; C. Harth; B. Greally; F.A. Van Woy; L.P. Steele; J. Muehle, G. Sturrock, F.N. Alyea, J. Huang, and D.E. Hartley

DOI

10.3334/CDIAC/atg.db1001

Description

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 six anthropogenic gases (chlorofluorocarbons CFCl₃, CF₂Cl₂, and CF₂ClCFCl₂); methyl chloroform, CH₃CCl₃; chloroform, CHCl₃; and carbon tetrachloride, CCl₄) have been carried out at five 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), HFC-365mfc(CF₃CH₂CF₂CH₃), methylene chloride (CH₂Cl₂), trichloroethylene (C₂HCl₃), and tetrachloroethylene (C₂Cl₄). 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. Units are dry air mole fractions in parts per 10¹² (picomoles/mole) for all halocarbons and SF₆, and parts per 10 ⁹ (nanomoles/mole) for nitrous oxide, methane, carbon monoxide and hydrogen.

The program, which began in 1978, is divided into three parts associated with three changes in instrumentation: the Atmospheric Lifetime Experiment (ALE), which used Hewlett Packard HP5840 gas chromatographs; the Global Atmospheric Gases Experiment (GAGE), which used HP5880 gas chromatographs; and the present Advanced GAGE (AGAGE). AGAGE uses two types of instruments: a gas chromatograph with multiple detectors (GC-MD), and a gas chromatograph with mass spectrometric analysis (GC-MS). The GC-MD is a new fully automated system produced at the Scripps Institution of Oceanography and includes a custom-designed sample module plus HP5890 and Carle AGC-211 gas chromatographic components. The original GC-MS was a fully automated system produced at the University of Bristol and comprised of an adsorption-desorption preconcentration module and an HP5973 gas chromatographic and mass spectrometric module. Beginning in January 2004, an improved cryogenic preconcentration system (Medusa) replaced the absorption-desorption module in the GC-MS systems at Mace Head and Cape Grim; this provided improved capability to measure a broader range of volatile perfluorocarbons with high global warming potentials. The Medusa system is now used at all five current AGAGE stations. Further details on this upgrade may be found at the AGAGE home page.

http://agage.eas.gatech.edu/instruments-gcms-medusa.htm

The current station locations are Cape Grim, Tasmania (41° S, 145° E), Cape Matatula, American Samoa (14° S, 171° E), Ragged Point, Barbados (13° N, 59° W), Mace Head, Ireland (53° N, 10° W), and Trinidad Head, California (41° N, 124° W). Stations also previously existed at Cape Meares, Oregon (45° N, 124° W), and Adrigole, Ireland (52° N, 10° W). The Mace Head station came on line in January, 1987 as a replacement for the Adrigole station which ceased operations at the end of December, 1983; the Trinidad Head station began operations during AGAGE in October 1995, as an essential replacement for the Cape Meares station from which GAGE data were not available after June, 1989.

Data from all three experiments are posted. AGAGE data through March 2008 are now available for all five existing sites. 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). Please see the "readme" files and (for gc-md) the "COcalibration.doc" and "H2calibration.doc" files for information on calibration of individual species.

Two sets of monthly data appear for the multiple-detection (md) species. These are: (1) data representing all samples, including those taken when the air was from directions where pollution may be present, and (2) data representing only those samples taken when the wind was from a direction representing background air. Data sets summarizing all samples, including potentially polluted air, end with the letter "p" as in xYmop, or for sulfur hexafluoride (tSF6.sup).

More extensive information about AGAGE may found from the AGAGE home page.

Reference:

• Prinn, R.G., R.F. Weiss, P.J. Fraser, P.G. Simmonds, D.M. Cunnold, F.N. Alyea, S. O'Doherty, P. Salameh, B.R. Miller, J. Huang, R.H.J. Wang, D.E. Hartley, C. Harth, L.P. Steele, G. Sturrock, P.M. Midgely, and A. McCulloch. 2000. A history of chemically and radiatively important gases in air deduced from ALE/GAGE/AGAGE. Journal of Geophysical Research 105: 17751-17792.

¹No longer used for sampling. Replaced by the station at Mace Head, Ireland (53° N, 10° W).
²No longer used for sampling. Replaced by the station at Trinidad Head, California (41° N, 124° W).
³More recent CFC-113 is included in the gc-ms-medusa file.
⁴Carbon monoxide (CO) data for Cape Grim, Tasmania, after December, 1999 is also temporarily removed in this update due to a non-linear problem. It will be added after appropriate correction is applied.
⁵Recent Medussa trichloroethylene (CHClCCl₂) and perchloroethylene (tetrachloroethylene)(CCl₂CCl₂) data have not been subjected to "blank correction". Those data are still preliminary and will be updated after the blank correction is applied.

Updated December 2008.