Abstract
The Pilot Study CCQM-P188 was conducted in parallel with the key comparisons CCQM-K120.a and CCQM-K120.b, which were designed to evaluate the level of compatibility of participants capabilities for value assigning carbon dioxide in air reference gas mixtures in the range (380-800) µmol/mol. It included two participants which did not take part in the key comparisons for the following reasons:
The Central Analytical Laboratory (CAL) of ICOS (Integrated Carbon Observation System) participated as an expert guest laboratory. The ICOS-CAL aims to ensure the accuracy of ICOS atmospheric measurement data as well as their traceability to the WMO scale. It provides reference gases for calibration of continuous in-situ measurements performed at monitoring stations, including real air reference gas with a certified value of carbon dioxide in air. It was agreed by the GAWG that its participation in this comparison would be of value to participating NMISs/DIs and bring a second link to the WMO scale as maintained by NOAA, which is itself a participant of the comparison as a designated institute by WMO.
The second participant was the BIPM, which took part as a participant with its PVT-CO2 facility, which was still under development at the time of the comparison. It was the occasion for the BIPM to benchmark the performance of its system at its current state of development, based on accurate pressure measurements, using a method similar to that employed by NOAA1.
This study involved the simultaneous comparison of a suite of 2 gas standards prepared by ICOS and 3 gas standard values assigned by the BIPM against cylinders prepared by laboratories that took part in the key comparison CCQM-K120, using exactly the same protocol.
The same two measurement methods that were described in the CCQM-K120 comparison report [see Flores et al. 2018] were used to compare standards in CCQM-P188, notably GC-FID, and FTIR spectroscopic analysis (corrected for isotopic variation in the CO2 gases measured at the BIPM using absorption laser spectroscopy).
The reference value for a given gas standard in this Pilot Study was the predicted value and uncertainty from a calibration line derived from the self-consistent sets standards used to calculate the Key comparison reference values for CCQM-K120, to the extent possible with any deviations recorded and explained. Following the advice of the CCQM Gas Analysis Working Group, results from the FTIR method were used to calculate the key comparison reference values in CCQM-K120, and the reference values in this Pilot Study. Results obtained from the GC-FID are presented for information, except for the BIPM standard at 800 μmol mol-1 which was not measured by FTIR, so that a reference value calculated using GC-FID measurements had to be used.
KEY WORDS FOR SEARCH
FTIR, ICOS, CO2, GC-FID, Carbon dioxide at background level, Carbon dioxide at urban level, Delta Ray, CO2 gas standards
Main text
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).