About
About Clean Air Data
An independent environmental data platform making long-term US air quality information accessible, transparent, and actionable — built for people who need to make real decisions about where to live.
What Makes Us Different
Clean Air Data is not a government agency, not affiliated with any air quality product or service, and carries no commercial interest in where you choose to live. We exist for one reason: to make the EPA's official monitoring data more useful for everyday decisions.
Most air quality tools show you today's AQI — a snapshot that changes by the hour. That's useful if you're deciding whether to go for a run this afternoon. It's not useful if you're choosing a city to raise a family in, or if you have a respiratory condition and need to understand multi-year exposure patterns.
We built Clean Air Data around a different question: over the past five years, which cities have consistently had the cleanest air? Every score on this site has a publicly documented formula. Every number traces back to an EPA monitoring station. Nothing is estimated or modeled — only measured data counts.
Our Data Sources
EPA AirNow Monitoring Network
All historical air quality scores are derived exclusively from the U.S. Environmental Protection Agency's AirNow program — the official federal source for ambient air quality data. AirNow aggregates readings from thousands of ground-level monitoring stations operated by state, local, and tribal agencies across the United States. These stations measure criteria pollutants including PM2.5, PM10, ozone (O₃), carbon monoxide (CO), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂).
Our long-term rankings use annual PM2.5 concentration data and AQI day-count distributions from 2021 through 2025, sourced from the EPA's Air Quality System (AQS) database. This five-year window is long enough to reflect genuine air quality conditions while remaining recent enough to capture the effects of policy changes and wildfire trends.
Health Standards We Reference
To give scores meaningful health context, we benchmark data against two authoritative standards:
- EPA National Ambient Air Quality Standards (NAAQS): The US regulatory threshold for annual PM2.5 is 9.0 μg/m³ (revised 2024). Cities below this level meet the federal standard.
- WHO Air Quality Guidelines: The World Health Organization's 2021 guidelines set an annual PM2.5 target of 5.0 μg/m³ — stricter than the US standard, and the benchmark we use to identify top-performing cities.
Real-Time Forecasts
The 5-day AQI forecasts shown on city pages are powered by the World Air Quality Index (WAQI) project and OpenAQ, which aggregate near-real-time sensor readings globally. These forecasts are clearly labeled and kept separate from our historical long-term scores.
How Scores Are Calculated
The Clean Air Score (0–100) is a composite index calculated from six components, each weighted by its significance to long-term health outcomes. The formula is fully documented and reproducible — anyone with access to EPA AQS data can verify any city's score independently.
The five-year average of annual mean PM2.5 concentrations, the single strongest predictor of long-term respiratory health impact.
The percentage of days per year when AQI exceeds 100, capturing acute pollution events that affect sensitive populations.
Whether air quality is improving or worsening over the study period — a forward-looking signal for long-term residents.
How consistently air quality holds across seasons. High variability (e.g., wildfire smoke summers) penalizes otherwise clean cities.
Days when AQI exceeds 150 (Unhealthy). Rare but severe spikes matter disproportionately for at-risk individuals.
Cities without a direct EPA monitor are scored using the nearest qualifying station, with transparent distance disclosure on each page.
For the complete formula with weightings, data sources, and worked examples, read our full methodology page. Every score on this site is an honest summary of public data — not a prediction, not an estimate, and not a marketing claim.
Who Uses Clean Air Data
Our users share a common need: they want accurate, long-term environmental data to inform decisions that matter. The most common use cases we hear about:
Comparing cities before a move, particularly when children's health or outdoor lifestyle is a priority.
Individuals with asthma, COPD, or cardiovascular disease who need to evaluate long-term exposure before choosing where to live.
Agents and buyers who want objective environmental data when evaluating neighborhood quality and long-term property value.
Policy researchers, public health analysts, and data journalists looking for a clean, city-level summary of EPA monitoring data.
Accuracy and Limitations
We believe in being transparent about what our data can and cannot tell you:
- → Scores are based on official monitor data only. They reflect conditions at EPA-certified monitoring stations, not necessarily in every neighborhood of a city. Large cities can have significant within-city variation.
- → Historical ≠ predictive. A five-year track record is a strong signal, but air quality can change due to new industrial activity, wildfires, or policy shifts. Always check current AQI before outdoor activity.
- → We focus on PM2.5. While our data includes AQI (which covers multiple pollutants), PM2.5 is the primary driver of our scores because it is the pollutant most consistently linked to long-term health outcomes by peer-reviewed research.
- → Proxy monitors are disclosed. Cities without a dedicated EPA station are evaluated using nearby monitors. The distance and source are shown on every city page.
Contact & Feedback
We take data accuracy seriously. If you notice an error in a city's score, a missing monitoring station, or outdated information, please let us know.
📧 Email: [email protected]
We respond to data correction requests and partnership inquiries within 2–3 business days.
Last updated: March 2026