Methodology and Sources
=======================

Metric definition:
Annual PM2.5 design value (µg/m³).

Ranking logic:
Lower values rank higher.

Methodology extracted from article:
Methodology The ranking uses annual PM2.5 design value, a long-term fine particle concentration measure expressed in micrograms per cubic meter. The source table is from the American Lung Association State of the Air 2026 report, which ranks metropolitan areas using official EPA air quality data for 2022, 2023 and 2024. What the metric measures Annual PM2.5 measures fine particulate matter smaller than 2.5 micrometers. These particles can penetrate deep into the lungs and are linked to asthma attacks, cardiovascular stress, strokes, lung cancer risk and premature death. Ranking direction Lower values are better. The main table is sorted from the lowest annual PM2.5 design value to the highest value in the cleanest-city list. Time period and snapshot logic The 2026 label refers to the report cycle and publication snapshot. The underlying monitored air-quality years are 2022, 2023 and 2024, which are the quality-assured years used in the source report. Metro-area calculation Metropolitan areas are ranked by the highest annual PM2.5 design value among counties within the metro area, using the metropolitan definitions applied by the source report. Rounding and ties Values are shown to one decimal place in µg/m³, matching the source table. Equal values keep the same rank where the source table reports ties. What the metric does not measure Annual PM2.5 does not measure ozone days, short-term smoke spikes, indoor air, local street-level exposure, unmonitored neighborhoods or every source of environmental quality. AQI and annual PM2.5 are different tools. AQI is a daily public communication index for pollutants such as ozone and particle pollution. Annual PM2.5 is a long-term concentration measure that fits a stable ranking, but it can understate short episodes from wildfire smoke, dust events or winter inversions. Readers comparing the cleanest U.S. cities by air quality should use annual PM2.5 for long-term exposure and daily AQI for immediate decisions. Next: Full Ranking → Back to chart ↑

Sources extracted from article:
Sources American Lung Association - State of the Air 2026 Report Main source for the cleanest-city table, including Table 3b for year-round particle pollution and methodology notes on EPA data years, design values and metro-area ranking logic. https://www.lung.org/getmedia/32f0646d-c5de-4501-b0ac-07cd63c974d4/State-of-the-Air-2026-Report.pdf American Lung Association - Cleanest Cities Public cleanest-city page explaining year-round particle pollution rankings and how they differ from ozone and short-term particle pollution lists. https://www.lung.org/research/sota/city-rankings/cleanest-cities EPA AirData / Outdoor Air Quality Data Official EPA environment for outdoor air quality data collected by monitoring sites. Used as the underlying data system referenced by State of the Air. https://www.epa.gov/outdoor-air-quality-data AirNow - Air Quality Index Basics Used to distinguish daily AQI interpretation from annual PM2.5 design values and to explain why a clean annual value does not replace daily air-quality alerts. https://www.airnow.gov/aqi/

Limitations:
The dataset is generated from the published StatRanker article table. It inherits the limitations of the original source, metric definition, reporting period, rounding and coverage. The values should not be interpreted outside the stated unit and methodology.
