Air Quality Rankings for Indiana (2026)

Indiana has 36 cities tracked by EPA air-quality monitors, with a state-wide 5-year median AQI of 41 — roughly matching the national average of AQI 41. Huntington, Indiana ranks #1 with the cleanest air (AQI 31, Grade B), while Marion, Indiana sits at the bottom (AQI 57, Grade C). The rankings below are computed from the EPA Air Quality System (AQS), which aggregates daily AQI readings from federally certified monitors into annual averages. Cities are sorted by 5-year median AQI (lowest = cleanest = #1). The 5-year window smooths out year-to-year volatility from weather and wildfire events.

Indiana is on an improving trajectory: 30 of 36 monitored cities show measurably cleaner air over the past decade, against just 3 that are getting worse. That mirrors the broader national pattern of falling particulate and ozone pollution as cleaner vehicles, cleaner power generation, and tighter industrial standards take effect.

The dominant pollutant across 19 of 36 Indiana cities is Fine Particulate Matter (PM2.5). PM2.5 (fine particulate matter) is most often driven by combustion sources — vehicle exhaust, industrial emissions, residential wood burning, and increasingly wildfire smoke. It penetrates deep into lung tissue and the bloodstream and is the air pollutant most strongly linked to long-term health impacts. Other Indiana cities report Ground-Level Ozone (17) as their dominant concern.

The fastest-improving city in Indiana is Floyd, Indiana, with median AQI falling by 2.0 points per year. Steady improvement at that pace usually reflects fleet turnover (older diesels retiring), upwind power-plant retirements, or tighter regional emissions controls.

The city with the steepest decline is Knox, Indiana, where median AQI is rising by 0.3 points per year. Rapid deterioration in a single city usually points to either wildfire-smoke exposure (in the West) or a new local emissions source — a power plant, port, or freight corridor coming online.