Atmospheric oxygen as a tracer for fossil fuel carbon dioxide: a sensitivity study in the UK

Chawner, Hannah, Saboya, Eric, Adcock, Karina E. ORCID: https://orcid.org/0000-0002-8224-5399, Arnold, Tim, Artioli, Yuri, Dylag, Caroline, Forster, Grant L., Ganesan, Anita, Graven, Heather, Lessin, Gennadi, Levy, Peter, Luijkx, Ingrid T., Manning, Alastair, Pickers, Penelope A., Rennick, Chris, Rödenbeck, Christian and Rigby, Matthew (2024) Atmospheric oxygen as a tracer for fossil fuel carbon dioxide: a sensitivity study in the UK. Atmospheric Chemistry and Physics, 24 (7). 4231–4252. ISSN 1680-7324

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Abstract

We investigate the use of atmospheric oxygen (O2) and carbon dioxide (CO2) measurements for the estimation of the fossil fuel component of atmospheric CO2 in the UK. Atmospheric potential oxygen (APO) – a tracer that combines O2 and CO2, minimizing the influence of terrestrial biosphere fluxes – is simulated at three sites in the UK, two of which make APO measurements. We present a set of model experiments that estimate the sensitivity of APO simulations to key inputs: fluxes from the ocean, fossil fuel flux magnitude and distribution, the APO baseline, and the exchange ratio of O2 to CO2 fluxes from fossil fuel combustion and the terrestrial biosphere. To estimate the influence of uncertainties in ocean fluxes, we compare three ocean O2 flux estimates from the NEMO–ERSEM, the ECCO–Darwin ocean model, and the Jena CarboScope (JC) APO inversion. The sensitivity of APO to fossil fuel emission magnitudes and to terrestrial biosphere and fossil fuel exchange ratios is investigated through Monte Carlo sampling within literature uncertainty ranges and by comparing different inventory estimates. We focus our model–data analysis on the year 2015 as ocean fluxes are not available for later years. As APO measurements are only available for one UK site at this time, our analysis focuses on the Weybourne station. Model–data comparisons for two additional UK sites (Heathfield and Ridge Hill) in 2021, using ocean flux climatologies, are presented in the Supplement. Of the factors that could potentially compromise simulated APO-derived fossil fuel CO2 (ffCO2) estimates, we find that the ocean O2 flux estimate has the largest overall influence at the three sites in the UK. At times, this influence is comparable in magnitude to the contribution of simulated fossil fuel CO2 to simulated APO. We find that simulations using different ocean fluxes differ from each other substantially. No single model estimate, or a model estimate that assumed zero ocean flux, provided a significantly closer fit than any other. Furthermore, the uncertainty in the ocean contribution to APO could lead to uncertainty in defining an appropriate regional background from the data. Our findings suggest that the contribution of non-terrestrial sources needs to be better accounted for in model simulations of APO in the UK to reduce the potential influence on inferred fossil fuel CO2 using APO.

Item Type:	Article
Additional Information:	Data availability: The datasets generated and analysed during this study are available at: https://doi.org/10.5281/zenodo.7681834 (Chawner et al., 2023). The observational datasets are available on CEDA: Heathfield CO2 and O2. https://catalogue.ceda.ac.uk/uuid/bfc2483537a744dca8e3239278b6e522 (Adcock and Pickers, 2022). Weybourne CO2. https://catalogue.ceda.ac.uk/uuid/87fc265aab6b4aeb961e62da2cd6ca91 (Forster, 2022a). Weybourne O2. https://catalogue.ceda.ac.uk/uuid/b3f9714c956f428a840211e0184e23eb (Forster, 2022b). Funding information: This research has been supported by the Natural Environment Research Council (grant nos. NE/S004211/1, NE/I013342/1, NE/S004521/1, and NE/R011532/1).
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User:	LivePure Connector
Date Deposited:	27 Jul 2023 14:30
Last Modified:	07 May 2024 16:31
URI:	https://ueaeprints.uea.ac.uk/id/eprint/92715
DOI:	10.5194/egusphere-2023-385

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