Open dataset · CC BY 4.0
Annual AQI by state, 2025
A transparent rollup of EPA county summaries for 53 states and territories. County averages and shares of monitored days stay separate because they answer different questions.
- 53
- states and territories
- 74.9%
- of measured county-days rated Good
- 679
- unhealthy-or-worse county-days
What this file contains
One row per state or territory for 2025. The file publishes two deliberately separate summaries: “typical county good-day rate” gives every monitored county one vote, while “share of monitored days rated Good” weights every monitored day equally. Neither silently substitutes for the other.
- 53
- state and territory rows
- 17
- columns with explicit subjects
- 323,288
- county-days of measurement
- 100 days
- floor for named best/worst counties
Source: U.S. EPA Air Quality System annual summary (annual_aqi_by_county_2025). Observation year: 2025. Source refresh checked: August 2026.
What the columns mean
| Column | Meaning | Origin |
|---|---|---|
| state_fips, state | State or territory FIPS code and EPA geography name. | EPA |
| monitored_counties | County rows present in the annual release for this geography. | PlainAirData |
| county_days_with_aqi | Sum of county-days with a valid AQI reading. This is the denominator for good_day_share_pct. | PlainAirData |
| good_days … hazardous_days | Sum of county-days in each EPA AQI category. | PlainAirData |
| typical_county_median_aqi | Mean of county median AQIs. It is an average of subgroup medians, not a state-level median. | PlainAirData |
| typical_county_good_pct | Mean of county good-day rates, with every county weighted equally. | PlainAirData |
| good_day_share_pct | SUM(good_days) ÷ SUM(days_with_aqi) × 100, with every monitored county-day weighted equally. | PlainAirData |
| best_county_100d, worst_county_100d | Highest and lowest good-day rates among counties with at least 100 monitored days; blank if none qualifies. | PlainAirData |
| slug | PlainAirData URL key for the matching state page. | PlainAirData |
A mean of county percentages and a share of monitored days are not interchangeable. Both are included, named for their subjects and tested against their underlying sums.
Reuse and attribution
The underlying EPA measurements are public domain. This compilation, meaning the cleaning, joins and clearly labelled derived columns, is released under CC BY 4.0, which permits reuse of any kind with attribution.
Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page and both downloads execute the same state-rollup SQL. The 100-day superlative floor and both denominator contracts are pinned by the data-export test. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2025 EPA annual summary; source refresh checked August 2026.