Open dataset · CC BY 4.0
Annual AQI by county, 2025
The EPA's annual county air-quality summary, cleaned and joined, as a single CSV or JSON file. 1,002 counties across 53 states and DC.
- 1,002
- counties
- 74.9%
- of measured days rated Good
- 679
- unhealthy-or-worse days
What this file contains
One row per county for 2025: how many days had a valid AQI reading, how those days split across the six EPA categories, and the median, 90th-percentile and maximum AQI. Counts are DAYS WITH A READING, not calendar days, and that is the denominator every share here divides by.
- 1,002
- rows (one per county)
- 22
- columns, 20 of them EPA’s own
- 328,003
- county-days of measurement
- 2020–2025
- years available in the trend table
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 |
|---|---|---|
| days_with_aqi | Days with a valid AQI reading. The denominator for every share. | EPA |
| good_days … hazardous_days | Days falling in each of the six EPA AQI categories. | EPA |
| median_aqi, pct90_aqi, max_aqi | Median, 90th-percentile and worst single-day AQI for the year. | EPA |
| days_ozone … days_co | Days on which each pollutant was the AQI-defining one. | EPA |
| good_pct | good_days ÷ days_with_aqi × 100. | PlainAirData |
| slug | Our URL key, so a row joins to its county page. | PlainAirData |
Two columns are ours and are labelled as such; the other twenty keep EPA's semantics so a reader can diff this file against the source release directly.
Reuse and attribution
The underlying EPA measurements are public domain. This compilation, meaning the cleaning, the joins and the two 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. Every figure on this page is read from the same query the CSV and JSON endpoints serve, so the page and the downloads cannot state different totals. 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.