Air Quality in Oregon

Oregon earns an average Air Quality Grade of B, with a 5-year median AQI of 34 across 23 monitored areas — 7 points below 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. Oregon's 23 monitored areas collectively logged 842 days at "Unhealthy for Sensitive Groups" or worse over the last five years.

Oregon is bucking the national trend of broad improvement: 12 of 23 monitored areas are showing measurably worse air over the past decade, more than the 6 that are improving. Across the western U.S. that pattern usually traces back to expanding wildfire smoke exposure; elsewhere it can reflect rising local emissions from population or freight growth.

The dominant pollutant across 23 of 23 Oregon 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.

Within Oregon, the gap between best and worst is meaningful: Jefferson, Oregon tops the state with a Grade A and 5-year median AQI of 28, while Klamath, Oregon sits at the bottom with a Grade C and 5-year median AQI of 44. Local terrain, prevailing winds, and proximity to industrial or wildfire emission sources drive most of that within-state variation.

Jefferson, Oregon is the fastest-improving area in Oregon, with median AQI falling by 2.0 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.