Adrigole
Barbados
Cape Grim R.G. Prinn
R.F. Weiss
F.N. Alyea, D.M. Cunnold
P.J. Fraser
P.G. Simmonds
A.J. Crawford, R.A. Rasmussen
R.D. Rosen
Adrigole
Barbados
Cape Grim
Cape Meares
Mace Head
Samoa
(see record for individual site)
The Atmospheric Lifetime Experiment (ALE) included measurements of CFC-11 (CCl3F), CFC-12 (CCl2F2), and nitrous oxide (N2O) at five globally distributed sites beginning in July 1978 (Prinn et al. 1983). The experiment was designed to accurately determine the atmospheric concentrations and long-term trends of several important trace gases so that their global circulation rates and globally averaged atmospheric lifetimes could be calculated. Beginning in late 1981 at Cape Grim (Tasmania) and later at other sites, additional measurements were collected using a new instrument as part of the Global Atmospheric Gases Experiment (GAGE). By mid-1986, ALE had ended and was succeeded by GAGE at all sites except the Adrigole (Ireland) station, which closed in December 1983 and was replaced by the GAGE station at Mace Head in January 1987.
Air samples, collected 4 times daily for ALE and 12 times daily for GAGE, were drawn in through an air intake located 2-15 m above the instrument building and were moved along a stainless steel line by a noncontaminating metal bellows pump. The air was then filtered and dried to roughly 700 parts per million by volume (ppmv) of H2O. Halocarbon measurements were made by means of Hewlett Packard HP5840A (ALE) or HP5880A (GAGE) electron capture gas chromatographs fitted with two columns. Measurements of CFC-11, CFC-12, and N2O were made from a 2- or 3-mL air sample by using a 1.8-m × 6.4-mm isothermal (50° C) column packed with 80-100 mesh Porasil D. Measurements of CFC-11 were also made from a 5- or 7-mL air sample by using a column that was the same size and the same temperature as the first but packed with 10% SP2100 silicone coated on 100-120 mesh Supelcoport. The carrier gas consisted of a mixture of 95% argon and 5% methane. Halocarbon mixing ratios in the samples were determined from integrated chromatographic peak areas or, occasionally, peak heights, by comparison with peaks from the nearest (in time) run of a reference gas. The reference gas was prepared from primary standards by exponential dilution and coulometric techniques (see Rasmussen and Lovelock 1983).
All data were subjected to extensive review procedures to detect any errors or malfunctions. In general, the first 6 months of ALE and GAGE data at each site are less reliable than later data because of uncertainties associated with the start-up of a new field instrument (Prinn et al. 1990). Measurements were also flagged to reflect "pollution" events (i.e., contamination by air masses containing higher than background levels of the halocarbons being measured). Such events were detected by concurrent increases in at least three of the measured species, usually from among the compounds CFC-11, CFC-12, and methyl chloroform (Prinn et al. 1992). At the Adrigole site, the occurrence of measurable levels of perchloroethylene, an anthropogenic species that is usually well correlated with rises in the other measured halocarbons, was also employed as a means of detecting pollution episodes. For N2O, local pollution events were detected by a combination of forecasting (through the use of weather maps) and inspection of the data. For further details on methodology and data selection, see Prinn et al. (1983) and Cunnold et al. (1994).
CITE AS: Prinn, R.G., R. F. Weiss, F.N. Alyea, D. M. Cunnold, P. J. Frazier,
P.G. Simmonds, A.J. Crawford, R.A. Rasmussen, and R.D. Rosen. 1994. Atmospheric CFC-11
(CCl3F), CFC-12 (CCl2F2), and N2O
from the ALE/GAGE network. In Trends: A Compendium of Data on Global Change..
ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National
Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.
Date created 12/10/96 (jaw)
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