Air pollution has long been linked to health issues, especially asthma. Coal-fired power plants are a definitive source of air pollution. But it’s been difficult for scientists to attribute respiratory problems of people living near coal specifically to those coal plants, because a host of other factors come into play. But after four coal-fired power plants in Louisville, Kentucky, either retired the use of coal or were retrofitted with strict emissions controls, local asthma-related hospitalizations dropped, and individuals even used their inhalers less frequently—showing the impact an abrupt drop in coal-related emissions can have on people’s health.
The findings come from a study published in Nature Energy this week by Columbia University, Harvard, the Louisville Metro Department of Public Health and Wellness, Propeller Health, and others. Propeller, a subsidiary of medical equipment company ResMed, makes digital inhaler sensors to help people better manage their asthma. In 2012, the city of Louisville partnered with Propeller for a pilot called AIR Louisville, enrolling residents in a program to use these sensor-enabled inhalers and then using that data to understand how the local air quality impacts those with respiratory disease.
Between 2013 and 2016, when four coal plants near Louisville had a change in emissions—one switched to natural gas, while three others installed sulfur dioxide scrubbers, which remove SO2 emissions from the coal plant exhaust—researchers saw the opportunity to take advantage of a natural experiment.
“Coal-fired power plants emit a number of health-harming pollutants. That includes sulfur dioxide, nitrogen oxide, particulate matter, and mercury as well as other things,” says Joan Casey, lead author of the paper and assistant professor of environmental health sciences at Columbia University Mailman School of Public Health. “But we selected sulfur dioxide as our target because coal-fired power plants far and away are the number-one producers of sulfur dioxide in the United States, whereas they make up a much smaller portion of some of these other pollutants, and so it’s a nice way to be able to track coal-fired power plant-specific emissions.”
In 2015, when three of those four coal-power plants changed their operations, the researchers saw a 55% drop in coal-related emissions in Jefferson County, Louisville’s largest county. That change, Casey says, resulted in about three fewer asthma-related hospitalizations and emergency department visits per Jefferson County zip code per quarter the following year—or about 400 avoided hospitalizations and emergency department visits annually.
The SO2 scrubbers were also associated with a 17% drop in monthly average rescue inhaler use compared to before those scrubbers were installed, based on the data from Propeller sensors. This is something unique to the study, Casey says, since usually researchers ask people to self-record their inhaler use in a diary, but that often isn’t a consistent or accurate measure.
Less-frequent inhaler use isn’t as severe a measure of asthma as hospital visits—”You’re having a pretty bad asthma attack if you show up to a hospital or have an [emergency department] visit,” Casey says—but it’s an important outcome, she adds, to show the impact on someone’s everyday life. “It’s still dramatically going to improve quality of life for folks. There are going to be fewer missed school days, there’s going to be fewer missed work days,” she says. “And it’s a much more common outcome than a hospitalization or ED visit.”
This study didn’t look at the health differences along racial lines or socioeconomic status, both of which are correlated with more frequent asthma diagnoses and asthma deaths in the U.S. Casey hopes a future study could dive deeper into those disparities. Still, she thinks these findings could have big implications for the more than 25 million Americans with asthma.
“I hope it encourages people to stay the course, to continue installing emissions controls or potentially consider transitioning away from coal altogether to either natural gas or renewable energy sources that are far less polluting for our air,” she says. Even though those SO2 scrubbers do make a difference, the most powerful thing to do, she adds, is to retire the plants all together. With coal becoming increasingly riskier economically, that might be the best solution for investors as well.