Insights: Duluth, MN-WI metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 42 over 365 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 242 Good days (66%), 100 Moderate (27%), and 11 Unhealthy-for-Sensitive-Groups (3%). The 90th-percentile AQI finished at 79 while the highest single-day reading hit 216 (Very Unhealthy). Metro residents averaged roughly 19.9 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -7.9 points and the median AQI moved +1 points, which classifies the multi-year trajectory as worsening. The annual record contains 12 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Metros with comparable AQI profiles include Allentown-Bethlehem-Easton, PA-NJ (66.8% good, AQI 42); Amarillo, TX (78.4% good, AQI 42); Carson City, NV (86.2% good, AQI 42).