A World Meteorological Organization (WMO) Central Calibration Laboratory (CCL) is responsible for maintaining and distributing the WMO Mole Fraction scale for a specified gas in air. NOAA GML is the WMO, Global Atmosphere Watch (GAW) CCL for CO2, CH4, N2O, SF6, and CO.
|CO2||WMO X2019 New!||19||250-800 ppm|
|CH4||WMO X2004A||16||300-5000 ppb|
|CO||WMO X2014A||14||30-500 ppb|
|SF6||WMO X2014||17||2-20 ppt|
NOAA/GML also maintains internal scales for a number of trace gases that are not part of the set of WMO GAW CCL scales (CO2, CH4, CO, N2O, SF6).
Scales are defined by a specific set of primary standards. Mixing ratios (expressed as dry air mole fraction) are assigned to the primary standards based on the mean repsonse observed on GC-ECD or GC-MSD instruments. For ECD instruments, a polynomial fit relating response to mixing ratio is used to assign values. For GC-MSD it is simply the mean molar response.
Current calibration scales for a number of trace species measured by GML are summarized in the table below. The table defines each scale and conversion factors used to update data from older scales. This table was originally published in NOAA/CMDL Summary Report No. 27 (2004). The most recent version of this table is updated on this website.
The scales shown are tied to a specific set of primary standards [Hall et al., 2001] and named
according to the year in which they were adopted. Thus, the preparation and use of new primary
standards for a particular compound results in a new scale for that compound.
Also shown in Table 1 is the number of primary standards used to define
each scale and the concentration range of those standards.
|Species||Previous Scale||Current Scale||Note||N||Range|
|CFC-113||2003||no change||10||20-110 ppt|
|CH3CCl3||2003||no change||10||10-180 ppt|
|halon 1211||1996||2006||3||5||3-7 ppt|
|halon 1301||1990||2006||4||6||2-5 ppt|
|HCFC-141b||1994||no change||3||5-50 ppt|
|HCFC-142b||1994||no change||3||5-50 ppt|
|HFC-134a||1995||no change||2||5-10 ppt|
|CH3Cl||2003||no change||9||280-810 ppt|
|CH3Br||2003||no change||9||8-390 ppt|
|CHCl3||2003||no change||1||4-13 ppt|
|C2Cl4||2003||no change||8||5-14 ppt|
|CHBr3||2003||no change||2||5-11 ppt|