Air Quality in Pennsylvania

Pennsylvania earns an average Air Quality Grade of B, with a 5-year median AQI of 43 across 40 monitored areas — 2 points above 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. Pennsylvania's 40 monitored areas collectively logged 480 days at "Unhealthy for Sensitive Groups" or worse over the last five years.

Pennsylvania is on a clear improving trajectory: 29 of 40 monitored areas are showing measurably cleaner air over the past decade, versus only 9 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 25 of 40 Pennsylvania areas 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 monitored areas in the state report Ground-Level Ozone (15) as their dominant pollutant.

Within Pennsylvania, the gap between best and worst is meaningful: Wyoming, Pennsylvania tops the state with a Grade A and 5-year median AQI of 33, while Allegheny, Pennsylvania sits at the bottom with a Grade C and 5-year median AQI of 56. Local terrain, prevailing winds, and proximity to industrial or wildfire emission sources drive most of that within-state variation.

Wyoming, Pennsylvania is the fastest-improving area in Pennsylvania, with median AQI falling by 2.1 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.