Nearly half of the people in the U.S. live in areas with unhealthy levels of air pollution — and Louisville is one of those areas.According to air quality data from the American Lung Association (ALA), the new 2025 annual report covers data from 2021 to 2023, the most recent year available. Hearst's Data Team put together an interactive map provided a grade for each county, at least for the ones that monitor it (Read more below).Louisville has the worst air pollution grade of the state:You can get live air quality checks for Louisville here. | Check Current Air Quality Surrounding counties are slightly better, with Clark and Floyd counties in Indiana having a C, as well as Oldham County, KY.Louisville ranks alongside other nearby big cities like Indianapolis and Cincinnati, which also got failing grades. Wildfires are one of the biggest factors leading to unhealthy air, especially as the changing climate causes more extreme heat and drought. But emissions, industry, oil and gas extraction, mining and construction also pollute the air.Air quality was improving across the country after the passage of the 1963 Clean Air Act, Pruitt said, but 10 years ago, progress halted. Increasing extreme heat events and wildfires have led to more ozone and particle pollution — two ways of measuring air quality — reversing clean air improvements.Only 885 counties monitor air pollution and have a complete enough dataset to be included in the report. The other more than 2,250 counties either don’t have enough funding or population to monitor air quality.For a better breakdown of the data, and a more in-depth look at how deregulation could affect data, read Heart's full report here.