Proposed network calibration procedures

• Archive tank at each site
  – Detect any long-term drifts of the four calibration tanks
  – Detect any abrupt changes in the measurements caused by replacement of calibration tanks or maintenance activities

• Four traveling target tanks
  -Detect leaks between the calibration gas valve manifold and the leak-test valve, short-term calibration tank drifts, problems with flow rates, insufficient drying of the samples

• Roving system (using LICOR-7000) with independent calibration tanks
  -Detect leaks anywhere within the system, short-term calibration tank drifts, problems with flow rates, insufficient drying of the samples, instrument-dependent errors due to the use of the LICOR-820 rather than the LICOR-7000
  

Preliminary results of the 4th WMO Round-robin intercalibration report indicate that our calibrated results for the three tanks (Group 2) were 0.10, 0.03, and 0.01 ppm different from the NOAA-ESRL measured values.