For more information contact
Brad Hall (+1 303 497 7011)
Quality standards are essential in order to properly
interpret measurements of atmopsheric trace gases. We have been preparing
our own compressed gas standards for over 20 years. Standards for various
halocarbons including chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs),
hydrochlorofluorocarbons (HCFCs), methyl halides, halons, chlorinated
solvents, and other gases are prepared gravimetrically as primary standards
in our laboratory. These standards are then used to calibrate secondary
and tertiary gas mixtures that are used within NOAA as well as other federal,
state, and private laboratories world-wide. The secondary and tertiary
standards normally contain dried, natural air collected using a pumping
system located at Niwot Ridge, Colorado.
Gravimetric standards are prepared by mixing
aliquots of pure gaseous or liquid reagents with ultra-pure air.
Lower level standards are prepared by static dilution.
We use three types of cylinder for primary standards. The majority of our standards have been prepared in Aculife-treated aluminum cylinders (size AL-30 or AL-150) purchased from Scott Specialty Gases. For nitrous oxide and sulfur hexafluoride we use aluminum cylinders that are not Aculife-treated (purchased from Scott-Marrin Inc.). These cylinders are cleaned and filled with ultra-pure air prior to use. The third type of cylinder used is a stainless steel cylinder certified for transport at 900 psig (Essex Cryogenics). These electopolished cylinders are used primarily for compounds known to be unstable in Aculife-treated aluminum, such as CH3Br and CH3Cl. We are continuing to investigate the stability of a number of trace gases in various types of cylinders.
A number of gravimetric standards are often used to define a calibration scale. Scales are defined based on a specific set of primary standards. Scales are named according to the year in which they are adopted. Calibration Scales
We also prepare tertiary standards at near-ambient mixing
ratios for other organizations performing research related to our lab's
mission. Standards can be analyzed by gas chromatography with electron
capture or mass spectrometric detection. Our clients have included
the German Environmental Agency (UBA), US National Center for Atmospheric
Research (NCAR), US National Aeronautics and Space Administration (NASA),
Australian Commonwealth Scientific and Industrial Research Organisation
(CSIRO), South African Weather Service, University of Colorado, Harvard
University, and many other organizations. Calibration
Standard Reference Gases: Gravimetric Standards