Our instrumentation and calibration techniques evolved from ALE to GAGE to AGAGE. With the inauguration of each new phase, measurement frequency and the number of analyzed species increased.
Using gas chromatography (GC) with an electron-capture detector (ECD), the Atmospheric Lifetime Experiment (ALE) began operation in July 1978 (until about 1986). It measured five species (CCl3F (CFC-11), CCl2F2 (CFC-12), CH3CCl3, CCl4, and N2O) four times daily.
This gas chromatographic experiment was succeeded in the 1981-1985 time frame by the Global Atmospheric Gases Experiment (GAGE), which measured 3 additional gases (CCl2FCClF2 (CFC-113), methane (CH4), chloroform (CHCl3)) (by using a flame ionization detector (FID)), as well as the ALE suite of gases. The frequency of measurement was also increased to 12 times per day during GAGE period (1981-1996).
A third phase, the Advanced Global Gases Experiment (AGAGE) began over the 1993-1996 period. AGAGE, which continues to the present, has two instrumental components. First, a highly improved gas chromatograph multidetector (GC-MD) system (with ECD, FID, and mercuric oxide reduction detector (MRD)). It can measure 10 compounds (see table 1) 36 times per day. Second, an automated gas chromatograph-mass spectrometer with an adsorption-desorption system (ADS GC-MS) at two of our stations (Mace Head, Ireland (started in October 1994), and Cape Grim, Tasmania (started in January 1998)). This system can measure a wide range of hydrochloroflurocarbons, hydroflurocarbons (HCFC-141b, HCFC-142b, HFC-134a etc.), methyl halides (CH3Cl, CH3Br, CH3I) and the halons (e.g. H-1211, H-1301). A newly developed state of the art Medusa GC-MS instrument has recently been deployed (from November 2003 to June 2006) at all (five) AGAGE stations and at the Scripps Institution of Oceanography (SIO) calibration laboratory. These new Medusa instruments not only extend the number of species measured by original ADS instruments to 40 species (see table 1) but also double the frequency of measurements to 60 minutes per measurement. As a result of these improvements, the original ADS GC-MS instruments at Mace Head and Cape Grim were retired in December 2004. More detailed descriptions of individual instrument can be found by clicking respective buttons at the top of this page.
* Measured at Mace Head and Cape Grim Only.
(ppt = parts per trillion, ppb = parts per billion)
(ppt unless noted
|* CO||80-140 ppb||0.2|
|* H2||500-540 ppb||0.6|