Standard Reference Gases

NOAA Calibration Scales for Various Trace Gases

Last Update: January 2, 2008

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.

The Scale Summary Table defines each scale and conversion factors used to update data from older scales. This Table was published in NOAA/CMDL Summary Report No. 27(2004). The most recent version of this Table will be updated on this website.

Current Work:

  1. CFC-12: revision complete
  2. HFCs: HFC143a, HFC-23, HFC-32, CFC-13, HFC-125
  3. CF4 and C2F6
  4. Hydrogen: standards and analysis development in progress

Scale Definitions: Primary standards used to define each scale.

All Standards: JPEG graphics that show relationships among primary standards. Standards used to define current scales are shown in yellow, newer standards under evaluation are shown in purple, and obsolete standards are shown in brown.