After four Louisville, Kentucky, coal-fired power plants either retired coal as their energy source or installed stricter emission controls, local residents asthma symptoms and asthma-related hospitalizations and emergency room visits dropped dramatically, according to research published today in Nature Energy. Coal-fired power plants are known to emit pollutants associated with adverse health effects, including increased asthma attacks, asthma-related ED visits and hospitalizations. In 2014, coal-fired power plants accounted for 63% of economy-wide emissions of sulfur dioxide (SO 2) in the U.S.. Historically, Kentucky has ranked among the top five states in the U.S. for emissions from power generation. Starting with a pilot in 2012, the city of Louisville embarked on a project called AIR Louisville, which aimed to use data from Propeller Healths digital inhaler sensors to gain insights into the impact of local air quality on the burden of respiratory disease in the community. Between 2013 and 2016, one coal-fired power plant in the Louisville area retired coal as an energy source, and three others installed stricter emission controls. The researchers found that energy transitions in the spring of 2015 resulted in three fewer hospitalizations and ED visits per ZIP code per quarter in the following year. This translates into nearly 400 avoided hospitalizations and ED visits each year across Jefferson County.