Multiyear dual-isotope fingerprinting at South Asian receptor sites constrains carbon monoxide sources and enhanced oxidation.

Authors

Peng Yao, Henry Holmstrand, Carina van der Veen, Maria Elena Popa, Chloe A Brashear, Krishnakant Budhavant, Mohanan Remani Manoj, Joakim Romson, Abdus Salam, Thomas Röckmann, Örjan Gustafsson

Published in

Proceedings of the National Academy of Sciences of the United States of America. Volume 123. Issue 42. Pages e2606200123. Oct 20, 2026. Epub Oct 12, 2026.

Abstract

Carbon monoxide (CO) is an indirect short-lived climate forcer with uncertainties both in sources and its role in atmospheric oxidation. Based on nine winter-long dual-isotope campaigns at two South Asian receptor sites intercepting the continental outflow, we quantified CO source contributions and emission-sink dynamics. Combustion accounts for 68 to 74% of South Asia regional CO (including 34 to 37% from biomass burning) with secondary atmospheric oxidation contributing 26 to 32% (dominated by oxidation of nonmethane volatile organic compounds (NMVOCs) at 21 to 26%, with methane oxidation contributing 5.5 to 6.4%). These isotope-observational constraints suggest a twice higher role for atmospheric oxidation than in model estimates. Spatially, the absolute contributions of both primary and secondary CO decrease from the Indo-Gangetic Plain to the northern Indian Ocean, while the relative contribution of oxidation-derived CO increases, indicating enhanced secondary CO production near source regions. Observation-model comparison suggests that transport from the continental areas dominates CO over adjacent oceanic regions, with minor local production. During the COVID-19 emission perturbation, combustion-derived CO fell sharply in absolute terms, NMVOC-derived CO rose, and CH₄-derived CO remained stable, providing an observational constraint on the sensitivity of atmospheric oxidation to emission changes. Our results reveal a significant contribution of CO from atmospheric oxidation in South Asia, calling for a reassessment of regional emission-oxidation coupling in models and of mitigation strategies.

PMID:
42863050
Bibliographic data and abstract were imported from PubMed on 13 Oct 2026.

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