Insights: Walla Walla, WA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 40 over 243 measured days in 2025, which corresponds to a Good band and a Good metro-wide health grade. The monitored-day split lands at 205 Good days (84%), 38 Moderate (16%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 55 while the highest single-day reading hit 80 (Moderate). Metro residents averaged roughly 25.3 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by -86 and the median AQI moved +11 points, which classifies the multi-year trajectory as improving. The metro avoided any Unhealthy-tier days entirely, an outcome that typically reflects favorable wind patterns, lower industrial density, or effective regional emission controls. Metros with comparable AQI profiles include Berlin, NH-VT (85.4% good, AQI 40); Burlington-South Burlington, VT (91.2% good, AQI 40); Cambridge, MD (84.4% good, AQI 40).