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Improved asthma outcomes observed in the vicinity of coal power plant retirement, retrofit and conversion to natural gas


Coal-fired power plants release substantial air pollution, which included over 60% of US sulfur dioxide emissions in 2014. Such air pollution may exacerbate asthma, but direct studies of the health impacts linked to power plant air pollution are rare. Here we take advantage of a natural experiment in Louisville, Kentucky, where one coal-fired power plant was retired and converted to natural gas, and three others installed SO2 emission control systems between 2013 and 2016. Dispersion modelling indicated that exposure to SO2 emissions from these power plants decreased after the energy transitions. We used several analysis strategies, which include difference-in-differences, first-difference and interrupted time-series modelling to show that the emissions control installations and plant retirements are associated with a reduced asthma disease burden related to hospitalizations and emergency room visits at the ZIP-code level, and to individual-level medication use as measured by digital medication sensors.

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Fig. 1: Power plant locations, emissions and exposure.
Fig. 2: Quarterly mean ZIP code-level HyADS exposure in Jefferson County.
Fig. 3: Quarterly ZIP-code-level counts of asthma hospitalizations and ERVs in Jefferson County.
Fig. 4: Spring 2015 coal-fired power plant events and counts of ZIP-code-level asthma hospitalization and ERVs.
Fig. 5: Monthly mean ZIP-code-level HyADS exposure from the Mill Creek power plant in Jefferson County, 2015–2017.
Fig. 6: Monthly average daily SABA use before and after the June 2016 Mill Creek SO2 scrubber installation.

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Data availability

The ZIP-code-level asthma hospitalization and ERV data are available from the authors following the submission of an analysis proposal and written approval granted by the Louisville Metro Public Health and Wellness. The AIR Louisville monthly medication use data are considered Protected Health Information under the Health Insurance Portability and Accountability Act of 1996 (HIPAA) in the United States, and as such may be accessible from the authors for analysis only after specific written authorization of access following HIPAA guidelines and Institutional Review Board approval. We provide Jefferson County ZIP-code-level monthly HyADS estimates on GitHub at

Code availability

An R package is available on GitHub for running the HyADS model ( We also provide analysis code on GitHub at


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We acknowledge the network of local partners that made the AIR Louisville program possible, which include the Center for Healthy Air, Water and Soil, Louisville Metro, the Community Foundation of Louisville and all the AIR Louisville participants. Partners within the Louisville Metro Government include G. Fischer, the Office of Civic Innovation, Louisville Metro Department of Public Health and Wellness, the Office of Sustainability, the Office of Advanced Planning, the Louisville Jefferson County Information Consortium and Louisville Forward. Specifically, K. Talley, M. King and R. Hamilton of the Air Pollution Control District provided critical information and review of this manuscript. We also thank P. Tarini and O. Wójcik at the Robert Wood Johnson Foundation for helpful guidance throughout the project. The main funding for the project was provided by the Robert Wood Johnson Foundation. Support was also provided by the Foundation for a Healthy Kentucky, Norton Healthcare Foundation, Owsley Brown Charitable Foundation, the American Lung Association, the National Institute of Environmental Health Sciences (J.A.C., K99/R00 ES027023; A.M.N, K99/R00 ES027511; C.Z., R01 ES026217) and the USEPA (C.Z., EPA 83587201). The contents of this work are solely the responsibility of the grantee and do not necessarily represent the official views of the USEPA or the Robert Wood Johnson Foundation. Further, the USEPA does not endorse the purchase of any commercial products or services mentioned in the publication.

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J.A.C., T.S. and M.A.B. secured funding for the study. J.A.C., J.G.S., L.R.F.H., C.Z., A.M.N., R.C., S.S.M., Y.-T.C., J.S. and M.A.B. designed the study and provided exposure and outcome data. J.A.C. and A.M.N. carried out the statistical analyses. J.A.C., J.G.S., L.R.F.H., C.Z., A.M.N., R.C., R.G., Y.-T.C., L.K., S.S.M., V.C., G.S., T.S., J.S. and M.A.B. reviewed and critically revised the manuscript.

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Correspondence to Joan A. Casey.

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M.A.B., R.G. and L.K. are salaried employees of Propeller Health and J.G.S. receives limited funding from Propeller Health to conduct analyses.

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Supplementary Figs. 1–11, Tables 1–5, Notes 1 and 2, and refs. 1–3.

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Casey, J.A., Su, J.G., Henneman, L.R.F. et al. Improved asthma outcomes observed in the vicinity of coal power plant retirement, retrofit and conversion to natural gas. Nat Energy 5, 398–408 (2020).

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