NOAA Calibration Scales for Various Trace Gases

Scales for WMO GAW CCL

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.

Click on species label for more information on the scale for that species.
Species Current Scale N Range
CO2WMO X2019 New!19250-800 ppm
CH4WMO X2004A16300-5000 ppb
COWMO X2014A1430-500 ppb
N2ONOAA-2006A14260-370 ppb
SF6WMO X2014172-20 ppt

Scales for other Gases

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.

Click on species label for more information on the scale for that species.
Species Previous Scale Current Scale Note N Range
CFC-12 2001 2008 1 15 150-650 ppt
CFC-11 1992 2016 5 100-260 ppt
CFC-113 2003 no change 10 20-110 ppt
CH3CCl3 2003 no change 10 10-180 ppt
CCl4 1996 2008 2 7 25-150 ppt
halon 1211 1996 2006 3 5 3-7 ppt
halon 1301 1990 2006 4 6 2-5 ppt
HCFC-22 1992 2006 5 9 75-200 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
HFC-152a None 2004 2 5-11 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
CH2Cl2 1992 2003 1 6-35 ppt
C2Cl4 2003 no change 8 5-14 ppt
COS 2002 2004 6 7 260-625 ppt
CHBr3 2003 no change 2 5-11 ppt
CH2Br2 2003 2004 7 2 10-20 ppt
Benzene None 2006 2 50-100 ppt
Ethane 2007 2012 6 0.5-40 ppb


1 - The 2008 CFC12 scale is 1.3% higher than the 2001 scale, see scale page for more information. Update using Y = 1.002*X + 5.807 ppt
2 - Seven standards prepared from 2001-2004 are now used to define te scale. These seven standards are consistent to within 0.5%. Four standards prepared in 1996 have been removed from the scale. For ECD-based results the conversion in 0.9954 at 95 ppt. For GCMS results the conversion is 0.9853.
3 - The 2006 scale is 1% higher than the 1996 scale. The conversion factor is 1.011.
4 - The 2006 halon-1301 scale is 13% higher than the 1996 scale. The conversion factor is 1.13.
5 - Five standards were added to the four than defined the 1992 scale. The 2006 scale is 0.5% higher than the 1992 scale.: Conversion factor 1.005.
6 - Two Aculife-treated standards were replaced by stainless steel standards in 2004.
7 - The scale change is in name only. The original assigment of 2003 was in error.