Quantifying combined uncertainties of d13C-CO2 & d18O-CO2 from 20-year calibration datasets: how good we could achieve in realization of VPDB-CO2 scale via NBS19 etc. carbonates?
by Dr. Lin Huang, Mrs./Ms. Alina Chivulescu, Mrs./Ms. Wendy Zhang

Abstract

To improve uncertainties in CO2 flux estimation using multiple atmospheric observation records via inversion models, it is important to quantify the combined uncertainties for each individual components, including isotope tracers (d13C-CO2 or d18O-CO2). Combined uncertainty is quantified via propagation of the uncertainties associated with each individual steps through a traceability path to the primary references. The primary scale of d13C-CO2 or d18O-CO2 is VPDB-CO2. One of the primary standard/reference is NBS19 (carbonate) with assigned isotopic values. To tie atmospheric d13C-CO2 or d18O-CO2 measurements to the primary scale, it needs linking the measurements to NBS19-CO2 through all levels of standards via a traceability path as realization of VPDB-CO2 scale. A direct and clear traceability path in realization of VPDB-CO2 scale has been utilized in ECCC’s lab over last 20 years for measuring CO2 isotope and BC isotope. We use two levels of carbonate standards (NBS19 as the primary standard, NBS18 and two additional lab carbonates as secondary standards). We calibrate/tie NBS18 and the two carbonates (Cal1 & Cal2) against/to the primary scale via NBS19-CO2 on an annual basis (measuring them together against the same working reference gas), and then we use secondary standards to tie our atmospheric sample measurements to VPDB-CO2 scale. The overall measurement uncertainty includes the uncertainties from the two levels, i.e., calibration for secondary standards via NBS19-CO2 and sample measurement against the secondary standards. Those uncertainties are usually associated with carbonate-CO2 production via acid digestion, IRMS analysis, and air-CO2 sampling/handling and CO2 extraction etc. In this presentation, we are going to focus on quantification of uncertainties at the first level, i.e., calibration of secondary carbonate standards against the primary standard (NBS19), a key step in realization of VPDB-CO2 scale. A 20-year-record of 13C-CO2 or d18O-CO2 by three different IRMS instruments (i.e., MAT252 over 2001-11, IsoPrime over 2002-14, and MAT253 over 2012-22) will be presented. The overall uncertainties for the periods by individual instruments as well as over the entire period of 20-year will be quantified and discussed. Those results would facilitate answering the question: how good we could achieve in realization of VPDB-CO2 scale over decadal time?

Video presentation

Poster

Topic : Theme 2: Accuracy requirements for atmospheric composition measurements across economic sectors, and temporal and spatial scales.
Reference : T2-A14

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