Insights: Seattle-Tacoma-Bellevue, WA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 48 over 243 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 137 Good days (56%), 106 Moderate (44%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 71 while the highest single-day reading hit 100 (Moderate). Metro residents averaged roughly 16.9 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by -59 and the median AQI moved -1 points, which classifies the multi-year trajectory as stable. 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 Brookings, SD (53.0% good, AQI 48); Charleston-North Charleston, SC (58.2% good, AQI 48); Chattanooga, TN-GA (53.9% good, AQI 48).