Abstract
Climate action ameliorates public health by reducing hazardous air pollutants alongside greenhouse gases, yet misguided mitigation efforts could induce imbalances in air pollution exchange across international borders. Despite its potential to endanger equality, the effects from climate action on transboundary air pollution are relatively unstudied. Here we show that stricter mitigation increases the fraction of co-benefits that originate externally in Africa by +8% in shared socioeconomic pathways (SSP) towards sustainability (SSP1) and by +53% for fragmentation (SSP3). The fraction of externally originating co-benefits is greater in developing countries (0.76 in SSP1-26) than developed (0.65), indicating that developing countries are more dependent on external action. Although co-benefits are maximized in the most ambitious scenario, SSP1-19 (1.32 million deaths avoided), their transboundary exchange between countries varies. These results suggest a need for climate policies that consider how inequalities in transboundary air pollution evolve across distinct socioeconomic trends and mitigation strategies in addition to total co-benefit estimates.
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Data availability
The emission projection data used in this study are publicly available for free from Fujimori et al. and accessible at: https://www.nature.com/articles/sdata2018210. The baseline disease rates, relative risk data, and population data are available from the Global Burden of Disease study (https://vizhub.healthdata.org/gbd-results/). The GEOS-Chem adjoint sensitivity calculations are available from the corresponding author upon request. The source data used to generate all of the main figures for this article and all source-receptor health estimates across the scenarios are freely available for open access on Zenodo (https://zenodo.org/records/18008107).
Code availability
The GEOS-Chem adjoint source code used to calculate adjoint sensitivities is publicly available, and instructions for downloading it can be found on the GEOS-Chem Adjoint Wiki: https://wiki.seas.harvard.edu/geos-chem/index.php/GEOS-Chem_Adjoint_Model.
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Acknowledgements
The authors acknowledge funding support from both NASA NNX16AQ19G and 80NSSC19K0193 for both M.O.N. and D.K.H. We additionally acknowledge funding support from Cardiff University’s Open Access fund for covering the article processing charges for this publication.
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M.O.N. and D.K.H. conceived and designed the study. M.O.N. and D.K.H.performed the simulations and processed the data. M.O.N. analyzed the data and developed the figures. M.O.N. wrote the initial draft of the manuscript. M.O.N. and D.K.H. contributed to the interpretation of the results, revised the manuscript, and approved the final version for submission.
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Nawaz, M.O., Henze, D.K. National climate action can ameliorate, perpetuate, or exacerbate international air pollution inequalities. Nat Commun (2026). https://doi.org/10.1038/s41467-026-68827-0
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DOI: https://doi.org/10.1038/s41467-026-68827-0
