Overview
The 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.
Table 1. AGAGE measured
species. Medusa in Blue;
GC-MD green; Both: Red
Compound |
~NH (2005) (ppt) |
Typical precision (%) |
Compound |
~NH
(2005) (ppt) |
Typical precision (%) |
CF4 |
74 |
0.15 |
H1301 |
3.1 |
1.5 |
C2F6 |
3.5 |
0.9 |
H1211 |
4.5 |
0.5 |
C3F8 |
0.5 |
3 |
H2402 |
>0.5 |
2 |
SF6 |
5.3 |
0.4 |
CH3Cl |
570 |
0.2 |
SO2F2 |
1 |
1.6 |
CH3Br |
10 |
0.5 |
HFC23 |
25 |
0.7 |
CH3I |
1 |
2 |
HFC32 |
~1 |
5 |
CH2Cl2 |
36 |
0.8 |
HFC134a |
29 |
0.4 |
CHCl3 |
11 |
0.6 |
HFC152a |
4.2 |
1.2 |
CHBr3 |
~3 |
0.6 |
HFC125 |
2.9 |
1 |
CCl4 |
95 |
1 |
HFC143a |
6.5 |
1.2 |
CH3CCl3 |
28 |
0.7 |
HFC365mfc |
<1 |
10 |
CHClCCl2 |
0.8 |
2.5 |
HCFC22 |
170 |
0.3 |
CCl2CCl2 |
5.5 |
0.5 |
HCFC141b |
19 |
0.4 |
C2H2 |
10-200 |
0.5 |
HCFC142b |
15 |
0.6 |
C2H4 |
50-500 |
2 |
HCFC124 |
1.6 |
2 |
C2H6 |
500 |
0.3 |
CFC11 |
257 |
0.15 |
C6H6 |
10-100 |
0.3 |
CFC12 |
546 |
0.05 |
C7H8 |
<1-10 |
0.6 |
CFC13 |
- |
2 |
GC-MD only* |
CFC113 |
80 |
0.2 |
CH4 |
1850 (ppb) |
0.05 |
CFC114 |
16.5 |
0.3 |
N2O |
320
(ppb) |
0.05 |
CFC115 |
8.4 |
0.8 |
CO |
130
(ppb) |
0.2 |
|
|
|
H2 |
500
(ppb) |
0.6 |
*CO and H2 are measured by GC-MD at Mace Head and
Cape Grim only
(ppt = parts
per trillion, ppb = parts per billion) |
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