Air Quality in Missouri

Missouri earns an average Air Quality Grade of B, with a 5-year median AQI of 41 across 21 monitored areas — right around the national average of 41. The grade combines four signals — 5-year median AQI, 10-year trend direction, count of unhealthy days per year, and dominant pollutant — into a single A-F score. Missouri's 21 monitored areas collectively logged 272 days at "Unhealthy for Sensitive Groups" or worse over the last five years.

Air quality in Missouri has held roughly steady over the past decade — 8 areas improving, 8 worsening, and 5 stable. That stability makes the state-average grade a reliable signal of what residents can expect.

The dominant pollutant across 11 of 21 Missouri areas is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs and triggers asthma — even healthy adults can feel it after exercising on high-ozone days. Other monitored areas in the state report Fine Particulate Matter (PM2.5) (10) as their dominant pollutant.

Within Missouri, the gap between best and worst is meaningful: Taney, Missouri tops the state with a Grade A and 5-year median AQI of 26, while St. Louis City, Missouri sits at the bottom with a Grade C and 5-year median AQI of 55. Local terrain, prevailing winds, and proximity to industrial or wildfire emission sources drive most of that within-state variation.

Taney, Missouri is the fastest-improving area in Missouri, with median AQI falling by 1.4 points per year over the EPA reporting period. Steady improvement at that pace usually reflects fleet turnover (older diesels retiring), upwind power-plant retirements, and tighter local emissions controls.