1. S.Assonov and M.Gröning (IAEA, Vienna)
Stable isotope reference materials at IAEA: addressing the GAW’ Data Quality Objectives, areas for potential collaboration with GAW.
S.Assonov and M.Gröning (IAEA, Vienna)
for the 3rd Meeting of the Environmental Pollution and Atmospheric Chemistry Scientific Steering Committee, WMO
March 15, 2016

2. Stable isotopes of air-CO2 & air-CH4:
fingerprints of the global carbon cycle.
CO2, mmol /mol
Alert (82N, 62 W, 200 masl)
Mauna Loa (19N, 155W, 3397 masl)
South Pole (89S, 24 W, 2810 masl)
d13C(CO2), ‰
Data by NOAA.
Very small variations;
Unique fingerprints of sources and processes involved in the global carbon-cycle;
Data from many labs, from many years

3. GAW’ Data Quality Objectives for stable isotopes:
Long-term compatibility goals: these challenges can be achieved by the proper use of Ref.Materials only. All calibrations are based on the highest-level Ref.Materails provided by the IAEA.
Needs for:
availability of reliable Ref.Materials,
understanding their uncertainty,
use of traceability and modern metrological concepts for uncertainty evaluation.
CCL for stable isotopes in CO2:
based on the IAEA materials,
presently no full uncertainty budget given,
improvements may be needed.

4. Stable isotope measurements:
Relative, artefact-based scales
δ13C = [(13C/12CSample)/(13C/12C)Standard - 1)],
expressed as parts of 1000, per mil, ‰
All isotope scales are artefact-based,
Relative measurements based on the use of Ref. Materials,
Measurements by mass-spectrometry require frequent calibrations,
New generation of laser-based optical analyzers (GHG concentrations and stable isotopes) need even more calibration mixtures,
Numerical values of (13C/12C)Standard are not well known. Thus relative calibrations are presently in use, these will be needed for decades.

5. Why Ref. Materials from IAEA are unique?
Highest-level standards, used to establish the entire calibration schemes for stable isotopes (d2H, d18O, d13C)
IAEA distributes realisations of these highest standards, these are Ref. Materials with the lowest possible uncertainty (NBS19);
“Fit-for-purpose” Ref. Materials are calibrated directly vs. highest standards.
Prototype of
kilogram ,
BIPM, Paris
Related metrology:
High-level standards are similar to the prototype of kilogram (at BIPM)
Work at the IAEA include the scale maintenance (introducing replacement materials),
Recommendations on the calibration schemes,
New materials with optimised uncertainty

6. Metrological institutes and stable isotope Ref. Materials
BIPM (and CCQM) does not work in this direction. BIPM invites the IAEA to lead their metrological work on CO2 stable isotope measurements;
IRMM (JRC-EC) does not make any stable isotope Ref. Materials;
NIST worked on stable isotope Ref. Materials in the past, presently this activity is stopped;
National metrological institutes – hardly any of them produces stable isotope Ref. Materials. They use IAEA-Ref.Materials for calibrations and invite the IAEA to collaborate on all relevant metrological aspects (e.g. HIGHGAS project);
Everyone make calibrations vs. stable isotope Ref.Materials from the IAEA. These are international materials.
IAEA is invited to collaborate with BIPM and metrologists.

7. Vision for 13C-RMs: family of carbonates & CO2
Highest-level international RMs – carbonates
2. Secondary international RMs – family of carbonates & CO2 gases.
Distribution: potentially in Cu-tube containers (alternative to glass ampoules)
Values: range of d13C & d18O of CO2; lowest uncertainty to be reached.
3. Tertiary, “fit-for-purpose RMs”:
Range of CO2 gases, next - CH4 gases;
User-friendly distribution (Cu-tubes, Alu-cans); optimized uncertainty.

8. Collaborations at IAEA: addressing the GAW needs
Ongoing work on suitable stable isotope RMs addressing the Data Quality Objectives for stable isotopes in greenhouse gases. RMs: carbonates & CO2 gases (for d13C & d18O in CO2), later - pure CH4 and maybe N2O. The gas RMs have to be easy to handle (crimped tubes, or containers with a valve);
IAEA contributes to an existing network of collaborations with BIPM and NMIs and builds new links (metrology of stable isotope RMs and calibrations);
to continue our role in the WMO-IAEA GGMT meetings, with recommendations concerning the best practice of stable isotope calibrations, also addressing the calibration strategy for new laser-optical analysers;
potentially contributing to find a suitable CCL for preparation and characterisation of stable isotope CO2-calibration mixtures (if such support is deemed useful by WMO);
potentially training users at IAEA on the best calibration approaches;
potentially in the future - contributing to find a suitable (informal) auditor for GAW laboratories analyzing stable isotopes in greenhouse gases.