# Counties in Virginia by share of days unhealthy for sensitive groups or worse (US EPA AQI), 1999

All 42 values come from U.S. Environmental Protection Agency for 1999, so the places are comparable. 18 counties have no value for that period and are not ranked.

- Indicator id: `aqi_unhealthy_sensitive_or_worse_days_share`
- Unit: %
- Definition: 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.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/unhealthy-air-quality-days-share/virginia-counties

| Rank | Place | % |
|---:|---|---:|
| 1 | Hanover County | 25.4 |
| 2 | Stafford County | 24.3 |
| 3 | Fauquier County | 20.7 |
| 4 | Madison County | 19.4 |
| 5 | Suffolk city | 18.7 |
| 6 | Henrico County | 18 |
| 6 | Page County | 18 |
| 8 | Giles County | 17.9 |
| 9 | Frederick County | 16.9 |
| 10 | Chesterfield County | 15.9 |
| 11 | Fairfax County | 15.6 |
| 12 | Wythe County | 14.5 |
| 13 | Arlington County | 13.7 |
| 14 | Prince William County | 13.4 |
| 15 | Caroline County | 13.2 |
| 16 | Charles City County | 12.5 |
| 17 | Hampton city | 12 |
| 18 | Loudoun County | 11.8 |
| 19 | Rockbridge County | 11.4 |
| 20 | Roanoke County | 9.3 |
| 21 | Prince Edward County | 8.1 |
| 22 | Alexandria city | 7.9 |
| 23 | Bristol city | 2.2 |
| 23 | Virginia Beach city | 2.2 |
| 25 | Chesapeake city | 1.8 |
| 25 | Lynchburg city | 1.8 |
| 27 | Richmond city | 1.6 |
| 28 | Newport News city | 1.3 |
| 29 | Norfolk city | 0.8 |
| 30 | Carroll County | 0 |
| 30 | Charlottesville city | 0 |
| 30 | Culpeper County | 0 |
| 30 | Fredericksburg city | 0 |
| 30 | King William County | 0 |
| 30 | Northumberland County | 0 |
| 30 | Roanoke city | 0 |
| 30 | Rockingham County | 0 |
| 30 | Salem city | 0 |
| 30 | Tazewell County | 0 |
| 30 | Warren County | 0 |
| 30 | Winchester city | 0 |
| 30 | Wise County | 0 |