Medusa-GCMS
The Medusa gas chromatograph-mass spectrometer (Medusa-GCMS) can measure a wide range of trace gas species through the use of pre-concentration techniques.
AGAGE calibration scales are used for all species measured in the network with the exception of CO2 and CH4. A standard calibration tank is measured alternately to each air measurement.
Calibration of the Medusa is controlled by a central calibration centre at Scripps Institute of Oceanography (SIO). Tanks of air (J-tanks) are filled here and calibrated against the gold standards here to assign concentration numbers to the range of species measured. These J-tanks are then sent out to the stations and used to calibrate measurements of Medusa species. J-tank standards are sent back to SIO once almost empty and re-measured to ensure no drift, loss or growth of any species has occurred within the tank whilst on site. In this way any drift can be monitored and corrected for. J-tanks are measured weekly against the H-tanks (air filled at Mace Head). These H-tanks are measured in every second run to ensure accurate calibration of all species. This method also means that the J-tanks last for up to 1 year rather whereas the H-tanks last for approximately 13 weeks.
Gas | AGAGE scale | Gas | AGAGE scale |
---|---|---|---|
CF4 | SIO-05 | CFC-11 | SIO-05 |
C2F6 (PFC-116) | SIO-07 | CFC-12 | SIO-05 |
C3F8 (PFC-218) | SIO-07 | CFC-13 | SIO-UB-p |
c-C4F8 | SIO-10-p | CFC-113 | SIO-05 |
HFC-23 (CHF3) | SIO-07 | CFC-114 | SIO-05 |
HFC-32 | SIO-07 | CFC-115 | SIO-05 |
HFC-134a | SIO-05 | H-1211 | SIO-05 |
HFC-152a | SIO-05 | H-1301 | SIO-05 |
HFC-125 | UB-98 | H-2402 | NOAA-1992-p |
HFC-143a | SIO-07 | CH3Cl | SIO-05 |
HFC-227ea | Empa-2005 | CH3Br | SIO-05 |
HFC-236fa | Empa-2009-p | CH3I | NOAA-Dec09 |
HFC-43-10mee | SIO-10-p | CH2Cl2 | UB-98 |
HFC-365mfc | Empa-2003 | CH2Br2 | NOAA-Jul10-p |
HFC-245fa | Empa-2005 | CHCl3 | SIO-98 |
HCFC-22 | SIO-05 | CHBr3 | NOAA-Dec09-p |
HCFC-141b | SIO-05 | CCl4 | SIO-05 |
HCFC-142b | SIO-05 | CH3CCl3 | SIO-05 |
HCFC-124 | NOAA-2003B | CHCl=CCl2 (TCE) | UB-98 |
CFC-11 | SIO-05 | CCl2=CCl2 (PCE) | NOAA-2003B |