Open dataset · CC BY 4.0
Annual AQI by metro area, 2025
One EPA row for each of 504 Core Based Statistical Areas. These are CBSA monitoring summaries, not measurements inside city limits.
- 504
- CBSAs
- 69.8%
- of measured CBSA-days rated Good
- 467
- unhealthy-or-worse CBSA-days
What this file contains
One row per EPA Core Based Statistical Area for 2025: monitored-day counts across the six AQI categories plus median, 90th-percentile and maximum AQI. A CBSA can span multiple municipalities, so the file never relabels these rows as city measurements.
- 504
- rows (one per CBSA)
- 15
- columns, 13 from EPA
- 171,256
- CBSA-days of measurement
- CBSA
- the geography contract
Source: U.S. EPA Air Quality System annual summary (annual_aqi_by_cbsa_2025). Observation year: 2025. Source refresh checked: August 2026.
What the columns mean
| Column | Meaning | Origin |
|---|---|---|
| cbsa_code, name | EPA Core Based Statistical Area code and name; this geography can contain multiple municipalities. | EPA |
| 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 |
| good_pct | good_days ÷ days_with_aqi × 100. | PlainAirData |
| slug | PlainAirData URL key for the matching metro-area page. | PlainAirData |
Day counts are days with a valid AQI reading, not calendar days. good_pct always divides by days_with_aqi; it never treats an unmonitored day as clean or polluted.
Every year: annual_aqi_by_cbsa_2020 to 2025
EPA publishes one file per year. Historical years carry fewer columns than the current one and no share column at all: this release retains no days_with_aqi per year, so there is no honest denominator, and the categories it does keep exclude unhealthy-sensitive, very-unhealthy and hazardous days, so summing them would undercount and overstate any percentage.
| EPA file | CBSAs | Download |
|---|---|---|
| annual_aqi_by_cbsa_2025 | 498 | CSV JSON |
| annual_aqi_by_cbsa_2024 | 501 | CSV JSON |
| annual_aqi_by_cbsa_2023 | 499 | CSV JSON |
| annual_aqi_by_cbsa_2022 | 504 | CSV JSON |
| annual_aqi_by_cbsa_2021 | 506 | CSV JSON |
| annual_aqi_by_cbsa_2020 | 504 | CSV JSON |
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. Every figure on this page is aggregated from the same ordered CBSA query the CSV and JSON routes serve; the page and downloads therefore share one population and denominator. 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.