# Share of days unhealthy for sensitive groups or worse (US EPA AQI) Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; the counts are stored with each value. ## Key facts - San Bernardino County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 1000 counties in 2019, at 36.4%, and York County the lowest, at 0%. Source: EPA. - Published for 1,498 places, with figures from 1980 to 2025. - Figures last updated on 2026-10-12. - Indicator id: `aqi_unhealthy_sensitive_or_worse_days_share` - Unit: % - Note: Use the share rather than the number of days to compare counties, since the days with an AQI differ. United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season. - Web page: https://invokely.ai/en/unhealthy-air-quality-days-share - API: https://invokely.ai/api/v1/indicators/aqi_unhealthy_sensitive_or_worse_days_share ## Rankings - [US counties](https://invokely.ai/rankings/unhealthy-air-quality-days-share/us-counties.md) (1498 places) - [Counties in Texas](https://invokely.ai/rankings/unhealthy-air-quality-days-share/texas-counties.md) (63 places) - [Counties in North Carolina](https://invokely.ai/rankings/unhealthy-air-quality-days-share/north-carolina-counties.md) (62 places) - [Counties in Virginia](https://invokely.ai/rankings/unhealthy-air-quality-days-share/virginia-counties.md) (60 places) - [Counties in California](https://invokely.ai/rankings/unhealthy-air-quality-days-share/california-counties.md) (58 places) - [Counties in Ohio](https://invokely.ai/rankings/unhealthy-air-quality-days-share/ohio-counties.md) (58 places) - [Counties in Kentucky](https://invokely.ai/rankings/unhealthy-air-quality-days-share/kentucky-counties.md) (55 places) - [Counties in Indiana](https://invokely.ai/rankings/unhealthy-air-quality-days-share/indiana-counties.md) (53 places) - [Counties in Michigan](https://invokely.ai/rankings/unhealthy-air-quality-days-share/michigan-counties.md) (53 places) - [Counties in Wisconsin](https://invokely.ai/rankings/unhealthy-air-quality-days-share/wisconsin-counties.md) (48 places) - [Counties in Oklahoma](https://invokely.ai/rankings/unhealthy-air-quality-days-share/oklahoma-counties.md) (45 places) - [Counties in Pennsylvania](https://invokely.ai/rankings/unhealthy-air-quality-days-share/pennsylvania-counties.md) (44 places) - [Counties in Florida](https://invokely.ai/rankings/unhealthy-air-quality-days-share/florida-counties.md) (42 places) - [Counties in Tennessee](https://invokely.ai/rankings/unhealthy-air-quality-days-share/tennessee-counties.md) (42 places) - [Counties in Colorado](https://invokely.ai/rankings/unhealthy-air-quality-days-share/colorado-counties.md) (40 places) - [Counties in Minnesota](https://invokely.ai/rankings/unhealthy-air-quality-days-share/minnesota-counties.md) (40 places) - [Counties in Georgia](https://invokely.ai/rankings/unhealthy-air-quality-days-share/georgia-counties.md) (39 places) - [Counties in New York](https://invokely.ai/rankings/unhealthy-air-quality-days-share/new-york-counties.md) (39 places) - [Counties in Montana](https://invokely.ai/rankings/unhealthy-air-quality-days-share/montana-counties.md) (36 places) - [Counties in Missouri](https://invokely.ai/rankings/unhealthy-air-quality-days-share/missouri-counties.md) (34 places) - [Counties in Washington](https://invokely.ai/rankings/unhealthy-air-quality-days-share/washington-counties.md) (34 places) - [Counties in Illinois](https://invokely.ai/rankings/unhealthy-air-quality-days-share/illinois-counties.md) (33 places) - [Counties in Alabama](https://invokely.ai/rankings/unhealthy-air-quality-days-share/alabama-counties.md) (31 places) - [Counties in Idaho](https://invokely.ai/rankings/unhealthy-air-quality-days-share/idaho-counties.md) (31 places) - [Counties in Louisiana](https://invokely.ai/rankings/unhealthy-air-quality-days-share/louisiana-counties.md) (30 places) - [Counties in Mississippi](https://invokely.ai/rankings/unhealthy-air-quality-days-share/mississippi-counties.md) (29 places) - [Counties in South Carolina](https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-carolina-counties.md) (28 places) - [Counties in Arkansas](https://invokely.ai/rankings/unhealthy-air-quality-days-share/arkansas-counties.md) (26 places) - [Counties in Iowa](https://invokely.ai/rankings/unhealthy-air-quality-days-share/iowa-counties.md) (26 places) - [Counties in Oregon](https://invokely.ai/rankings/unhealthy-air-quality-days-share/oregon-counties.md) (26 places) - [Counties in Nebraska](https://invokely.ai/rankings/unhealthy-air-quality-days-share/nebraska-counties.md) (24 places) - [Counties in Kansas](https://invokely.ai/rankings/unhealthy-air-quality-days-share/kansas-counties.md) (23 places) - [Counties in New Mexico](https://invokely.ai/rankings/unhealthy-air-quality-days-share/new-mexico-counties.md) (21 places) - [Counties in Wyoming](https://invokely.ai/rankings/unhealthy-air-quality-days-share/wyoming-counties.md) (21 places) - [Counties in New Jersey](https://invokely.ai/rankings/unhealthy-air-quality-days-share/new-jersey-counties.md) (20 places) - [Counties in West Virginia](https://invokely.ai/rankings/unhealthy-air-quality-days-share/west-virginia-counties.md) (20 places) - [Counties in Maryland](https://invokely.ai/rankings/unhealthy-air-quality-days-share/maryland-counties.md) (19 places) - [Counties in Utah](https://invokely.ai/rankings/unhealthy-air-quality-days-share/utah-counties.md) (19 places) - [Counties in Maine](https://invokely.ai/rankings/unhealthy-air-quality-days-share/maine-counties.md) (16 places) - [Counties in Arizona](https://invokely.ai/rankings/unhealthy-air-quality-days-share/arizona-counties.md) (15 places) - [Counties in North Dakota](https://invokely.ai/rankings/unhealthy-air-quality-days-share/north-dakota-counties.md) (15 places) - [Counties in South Dakota](https://invokely.ai/rankings/unhealthy-air-quality-days-share/south-dakota-counties.md) (14 places) - [Counties in Alaska](https://invokely.ai/rankings/unhealthy-air-quality-days-share/alaska-counties.md) (13 places) - [Counties in Massachusetts](https://invokely.ai/rankings/unhealthy-air-quality-days-share/massachusetts-counties.md) (13 places) - [Counties in Nevada](https://invokely.ai/rankings/unhealthy-air-quality-days-share/nevada-counties.md) (12 places) - [Counties in New Hampshire](https://invokely.ai/rankings/unhealthy-air-quality-days-share/new-hampshire-counties.md) (10 places) - [Counties in Vermont](https://invokely.ai/rankings/unhealthy-air-quality-days-share/vermont-counties.md) (7 places)