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Energy and health

Coal-fired power plant closures and retrofits reduce asthma morbidity in the local population

A Publisher Correction to this article was published on 14 May 2020

A Publisher Correction to this article was published on 14 May 2020

This article has been updated

Retiring, transitioning or installing more stringent emissions controls in coal-fired power plants has the potential to decrease asthma attacks and asthma-related emergency department visits and hospitalizations in nearby communities. These health co-benefits should be considered in policy and decision making about coal-fired power plant retirement or retrofit.

Messages for Policy

  • Retiring or converting power plants from coal to natural gas could confer health benefits on people with asthma.

  • In Louisville, Kentucky, coal-fired power plant retirements and SO2 control installations led to reductions in SO2 emissions and air pollution exposure.

  • This reduction in air pollution exposure translated into substantially fewer asthma-related emergency department visits and hospitalizations.

  • Given that 20.4 million adults, or about 9% of the population, suffer from asthma, the shift in US energy trends away from coal-fired electricity generation may reduce asthma morbidity below otherwise expected levels.

  • Digital health tools, such as wirelessly connected inhalers that track the time and date of medication use, can assist in analysing asthma symptoms outside the hospital and in gauging the impact of air pollution exposure on a community. They may serve as supplemental public health research tools in the future.

BASED ON J. A. Casey et al. Nature Energy (2020).

The policy problem

Coal-fired power plants provide a large amount of electricity worldwide. In 2015, they produced 6 trillion MWh, representing 25% of the global supply. Simultaneously, coal-fired power plants emit air pollution, including SO2, nitrogen oxides (NOx), particulate matter (PM2.5 and PM10), mercury, acid gases, polycyclic aromatic hydrocarbons and volatile organic compounds. Such pollutants have been associated with increased asthma symptoms, emergency room (ER) visits, hospitalizations and mortality. Studies have shown that exposure to SO2 drives higher levels of uncontrolled asthma, asthma symptoms and asthma-related hospitalizations among people living near coal-fired power plants and fossil fuel refineries. Between 2000 and 2015 in the US, many coal-fired power plants transitioned to natural gas or installed SO2 emission controls to comply with regulations from the US Environmental Protection Agency and state environmental agencies. Quantifying the health co-benefits of this transition is critical for assessing the holistic impacts of the regulation.

Fig. 1: Coal-fired power plant emissions exposures and asthma outcomes in Louisville, KY.

Results by ZIP codes highly exposed in the pre-period versus those that were not. a, Total HYSPLIT Average Dispersion (HyADS) model exposures from those units that retired or retrofitted in Q2-2015. b, Louisville-wide total quarterly counts of asthma hospitalizations and ER visits. Adapted with permission from Casey, J. A. et al. Nat. Energy (2020); Springer Nature Ltd.

The findings

Our study took advantage of a natural experiment that occurred between 2013 and 2016, when four coal-fired power plants in the Louisville, Kentucky area retired, transitioned to natural gas or installed SO2 emissions controls. We found that these coal-fired power plant changes translated into reduced asthma exacerbations among the local community. Among ZIP codes more exposed to coal-fired power plant emissions, there were three fewer hospitalizations or emergency department visits per ZIP code per quarter in the year following a major transition, which translates into nearly 400 avoided hospitalizations and ER visits each year across Jefferson County, where Louisville is located. At the level of individuals, a 2016 emissions control installation was associated with a 17% reduction in overall counts of rescue inhaler use in the following month, and a 32% reduction in the odds of having high rescue inhaler use (defined as 4 puffs per day on average per month).

The study

Our study used retirements and SO2 emission control installations at four coal-fired power plant facilities near Louisville, Kentucky, between 2013 and 2016 to frame a natural experiment. We equipped 207 Louisville residents with digital sensors for their asthma rescue inhalers and studied their inhaler use. We also tracked local hospitalization and ER visit data over time. We calculated changes in emissions exposure across the period using a model that tracks air pollution emitted from individual sources. We used that model to calculate the changes in exposure to emissions from each plant across time and space. Changes to plant emissions generated large and abrupt changes in air pollution exposure for local residents. We analysed ZIP-code level data on asthma-related hospitalizations and ER visits, as well as asthma symptoms measured at the individual level using digital inhaler sensors. Combined with information on population demographics, including socio-economic status changes over time, we used the coal-fired power plant emission exposure estimates and health data to assess the impact of air pollution changes on respiratory health.

Change history

  • 14 May 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


Further Reading

  1. Barrett, M. et al. AIR Louisville: addressing asthma with technology, crowdsourcing, cross-sector collaboration, and policy. Health Aff. 37, 525–534 (2018). Overview of the AIR Louisville cohort and Propeller’s digital medication sensors.

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  3. Henneman, L. R. F., Choirat, C., Ivey, C. E., Cummiskey, K. & Zigler, C. M. Characterizing population exposure to coal emissions sources in the United States using the HyADS model. Atmos. Environ. 203, 271–280 (2019). Technical article on the HyADS model used to estimate coal-fired power plant exposures.

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  4. Rich, D. Q. Accountability studies of air pollution and health effects: lessons learned and recommendations for future natural experiment opportunities. Environ. Int. 100, 62–78 (2017). Description of the utility of natural experiments to study air pollution and health outcomes.

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  5. Smargiassi, A. et al. Risk of asthmatic episodes in children exposed to sulfur dioxide stack emissions from a refinery point source in Montreal, Canada. Environ. Health. Perspect. 117, 653 (2009). Case-crossover study linking modelled daily SO 2 levels to asthma hospitalizations and ER visits in children.

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  6. 2016 National Health Interview Survey (NHIS) Data (CDC, accessed 28 February 2019); Report that states 9% prevalence of asthma in the United States.

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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 US Environmental Protection Agency (US EPA) (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 US EPA or the Robert Wood Johnson Foundation. Further, the US EPA does not endorse the purchase of any commercial products or services mentioned in the publication.

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Corresponding author

Correspondence to Joan A. Casey.

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Competing interests

The authors declare the following competing interests: 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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Casey, J.A., Su, J.G., Henneman, L.R.F. et al. Coal-fired power plant closures and retrofits reduce asthma morbidity in the local population. Nat Energy 5, 365–366 (2020).

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