Insights: Riverside-San Bernardino-Ontario, CA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 87 over 365 measured days in 2025, which corresponds to a Moderate band and a Very Poor metro-wide health grade. The monitored-day split lands at 27 Good days (7%), 202 Moderate (55%), and 83 Unhealthy-for-Sensitive-Groups (23%). The 90th-percentile AQI finished at 161 while the highest single-day reading hit 365 (Hazardous). Metro residents averaged roughly 2.2 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 +1.0 points (measured against 262 monitored days in 2020 and 277 in 2025, so raw day counts are not comparable) and the median AQI moved -11 points, which classifies the multi-year trajectory as improving. The annual record contains 53 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Metros with comparable AQI profiles include Phoenix-Mesa-Scottsdale, AZ (6.6% good, AQI 78); Los Angeles-Long Beach-Anaheim, CA (10.7% good, AQI 74); Bakersfield, CA (17.5% good, AQI 70).