Nitrous Oxide (N2O) WMO Scale
Update: March, 2025
The 2006A N2O scale is based on 13 primary standards prepared by static gravimetric dilution from 99.9% pure N2O in 5.9-L aluminum cylinders. All standards contain CO2 and SF6 at near ambient levels. Assigned values were determined by fitting a 2nd order polynomial to the response of each standard (relative to a 318 ppb natural air secondary standard) measured using an HP6890 GC with electron capture detection. Analysis precision was typically less than 0.05% (one standard deviation). The standard deviation of resuduals is 0.33 ppb.
Prior to February 2025, analysis for N2O was performed by gas chromatography with electron capture detection (Hall et al., 2006; Hall et al., 2011)
In 2024, we began testing a laser spectroscopic system (Tunable Infrared Laser Direct Absorption Spectroscopy, TILDAS) for analysis of N2O. This particular instrument was designed to employ detection of N2O and CO using independent absorption features, with no spectral overlap. The laser spectroscopic system is calibrated approximately every two weeks relative to a suite of 7 secondary standards, which were value-assigned by GC-ECD over multiple years. On average, results from the GC-ECD and laser spectrometer are consistent, and therefore we have officially adopted the laser-based TILDAS as the analytical method for N2O as of February 1, 2025. The new analyzer was run in parallel with the GC-ECD system from May 2022 - May 2023 and April 2024 - present. The data from the overlap period are available on the CCL website. The N2O scale is unchanged (X2006A), only the analytical method has changed.
A preliminary estimate of reproducibility for N2O based on laser spectroscopic analysis is 0.08 ppb (2-sigma).
References
- Hall, B. D., G. S. Dutton and J. W. Elkins (2007), The NOAA nitrous oxide standard scale for atmospheric observations, Journal of Geophysical Research-Atmospheres, 112, D09305, doi:10.1029/2006JD007954.
For N2O results, see the GML CCL Reference Gas Calibrations page.
| Cylinder | Year | Prepared (ppb) |
Assigned (ppb) |
Residual (ppb) |
|---|---|---|---|---|
| FA-1861 | 2000 | 261.30 | 261.20 | -0.10 |
| FA-1878 | 2000 | 314.66 | 314.04 | -0.62 |
| FA-1843 | 2000 | 331.34 | 331.57 | 0.23 |
| FA-1850 | 2000 | 315.98 | 315.68 | -0.30 |
| FA-1851 | 2000 | 302.12 | 302.22 | 0.10 |
| FA-1865 | 2000 | 288.29 | 288.88 | 0.59 |
| FA-2205 | 2003 | 315.39 | 315.40 | 0.01 |
| FA-2207 | 2003 | 333.01 | 333.54 | 0.53 |
| FA-2208 | 2003 | 357.33 | 357.46 | 0.13 |
| FA-2557 | 2005 | 291.36 | 291.39 | 0.03 |
| FA-2567 | 2005 | 320.98 | 321.04 | 0.06 |
| FA-2569 | 2005 | 336.08 | 335.81 | -0.27 |
| FA-2585 | 2005 | 371.37 | 371.27 | -0.10 |
