Our Mission

PlainAir exists because the air you breathe is one of the most important factors in long-term health, yet most people have no idea how their county's air quality compares to the rest of the country. The EPA collects excellent monitoring data from thousands of stations nationwide, but accessing it requires navigating bulk download files and technical documentation designed for environmental scientists.

We believe air quality data collected at public expense should be accessible to the people who breathe that air. PlainAir transforms EPA data into a modern, searchable format covering nearly 1,000 counties, 500+ metro areas, and all 50 states, making it possible for anyone to look up their area's air quality history, compare locations, and understand trends over time.

Data Source

All data on PlainAir comes from the EPA's Air Quality System (AQS), which collects ambient air quality data from thousands of monitoring stations across the United States. Our data covers 2020-2025 and includes annual AQI summaries by county and metropolitan area.

What We Track

• Counties: Air quality data for nearly 1,000 U.S. counties with AQI breakdowns, pollutant days, and 5-year trends.
• Metro Areas: AQI summaries for 500+ metropolitan statistical areas (CBSAs).
• States: Aggregated state-level summaries computed from county-level data.
• Rankings: Best and worst air quality rankings for counties, metros, and states.

Key Terms

• AQI (Air Quality Index): A scale from 0-500 measuring air pollution levels. Lower is better.
• Good Days (0-50 AQI): Air quality is satisfactory, posing little or no risk.
• Moderate Days (51-100 AQI): Acceptable quality; some pollutants may affect very sensitive individuals.
• USG Days (101-150 AQI): Unhealthy for Sensitive Groups, people with lung disease, older adults, children, and active people may be affected.
• Unhealthy Days (151-200 AQI): Everyone may begin to experience health effects.
• Primary Pollutant: The pollutant that drives the AQI reading on a given day (ozone, PM2.5, PM10, NO2, or CO).

Data Currency

PlainAir currently displays data from the EPA Air Quality System 2020-2025 annual summary files. The 2024 data represents the most recent complete calendar year available. EPA publishes annual AQI summary files typically within 6-9 months of the reference year's end. We update PlainAir within 30 days of each new annual data release.

Five-year trend data (2020 through 2024) is presented where available, providing a window into whether air quality in a given area has been improving or declining. Not all counties have monitoring data for all five years, new monitoring stations come online and others are decommissioned. Trend data requires at least three years of coverage to be meaningful.

For real-time air quality conditions, visit AirNow.gov. PlainAir shows historical annual data, not current conditions.

Editorial Independence

Content on PlainAir is compiled by our editorial team. Raw EPA air quality data is transformed into readable county and state profiles by our continuous editorial pipeline, then validated against the source before publication. The PlainAir editorial team, is responsible for editorial standards, methodology, and corrections.

We do not accept payment, sponsorship, or promoted placement from government agencies, environmental organizations, or any other covered entity. Our only revenue source is contextual display advertising served by Google AdSense, advertisers do not influence which areas or data we cover, and they do not receive preferential placement.

Limitations

• Not all counties have monitoring stations. Data reflects only monitored areas.
• AQI data represents annual summaries, not real-time readings.
• State-level figures are averages of monitored counties only and may not represent the entire state.
• EPA publishes data with a delay. Our most recent year is 2024.

Disclaimer

PlainAir is not affiliated with, endorsed by, or connected to the U.S. Environmental Protection Agency or any government agency. This site is for informational purposes only. For real-time air quality and health guidance, visit AirNow.gov.

Contact

Questions or feedback? Reach out at hello@plainairdata.com.

How We Process Air Quality Data

PlainAir downloads annual AQI summary files from the EPA Air Quality System and loads them into a structured database. County-level readings, including good, moderate, and unhealthy day counts plus primary pollutant breakdowns, are the foundation. Metro-area and state summaries are computed by aggregating data from the monitored counties within each geography, not by interpolating for counties without monitoring stations.

Five-year trend data (2020 through 2024) is presented where available, giving a window into whether air quality in a given area has been improving or declining. Rankings are based on median AQI, a straightforward metric that reflects the typical day, not just the worst episodes.

Important Disclaimer

This site is for informational purposes only. Data may not reflect current conditions. Do not rely solely on this data for personal safety decisions. Always follow official guidance from local authorities and emergency services.