Calibration for atmospheric nitrous oxide observation
JMA operates a nitrous oxide (N2O) calibration system to maintain N2O standard gases with two ranks.
JMA standard gases
JMA primary standard gases
In the first rank of gases on which JMA's N2O observations are based, the primary standard gases for N2O are stored in five cylinders with concentrations ranging from about 280 to 340 ppb. The cylinders used to store these gases, which are mixtures of N2O and natural air, have a volume of 48 liters and are made of aluminum alloy to minimize drift. The concentrations of the primary gases were determined accurately against the WMO reference standard gases maintained by NOAA/ESRL in December 2006 (Hall et al. 2007) . The standard scale is called NOAA 2006A, and assures the international traceability of JMA's observations.
JMA working standard gases
The concentrations of working standard gases (the second-rank gases used at Ryori and stored in four 9.4-liter aluminum cylinders) are determined using the N2O calibration system at JMA Headquarters based on the primary standard gases, and these working standard gases are then sent out to Ryori. After use in observation, the gases are sent back to JMA Headquarters to be checked for drift, and the concentrations are compared with those of the primary standard gases (see Atmospheric nitrous oxide observation ) .
Calibration system
The calibration system for N2O concentration is configured using a gas chromatograph analyzer with a radiative electron capture detector (GC-ECD: Shimadzu Corporation, GC-2014) . The repeatability of the N2O calibration system does not exceed 3 ppb, which is determined by introducing standard gases ten times and taking the standard deviation for the mean peak area.
Figure 1: N2O calibration system at JMA headquarters |
Figure 2: JMA Calibration architecture for N2O standard gases |
References
Hall, B. D., G. S. Dutton, and J. W. Elkins, 2007: The NOAA nitrous oxide standard scale for atmospheric observations, J. Geophys. Res., 112, D09305, doi:10.1029/2006JD007954.