Cities With Stable Air Quality
These cities have maintained consistent air quality over the past decade with no significant improvement or decline.
What "Stable" Air Quality Actually Means
A city qualifies as "stable" when its 10-year linear regression on annual median AQI shows a slope between -0.1 and +0.1 AQI points per year — neither measurably improving nor worsening over the period. Stability is a useful baseline: residents can plan around what they know about local air without expecting major changes from year to year. But stability can mean either of two very different things — a clean city that is not eroding, or a polluted city that is not improving.
Why Air Quality Stays Stable
Stable air quality usually reflects a balance: emission reductions from cleaner vehicles and power plants are being offset by population growth, traffic increases, or periodic wildfire-smoke events. Cities that have been "average pollution" for decades tend to stay that way unless something changes — a major refinery closes, a new freight hub opens, or wildfire smoke becomes a regular summer fixture. Stability is also more common in mid-density, mid-population cities without major recent industrial change.
Health Impact
Stability is a mixed signal — good news for clean cities, bad news for polluted ones. Residents of stable Grade A or B cities are essentially in maintenance mode: current health protections are adequate as long as conditions hold. Residents of stable Grade D or F cities should not expect outdoor air quality to improve naturally; their best leverage is on indoor air quality (HEPA, HVAC filtration), exposure planning, and local advocacy for emission-reduction policies.
What to Watch
Stability can break in either direction. Watch for new industrial development, freight corridors, or port expansions that could push a stable-clean city toward worsening. Watch for vehicle fleet turnover, transit investment, or upwind power-plant retirements that could push a stable-polluted city toward improving. Watch for changing wildfire patterns: a stable Western city today may show worsening trends within a few years if wildfire activity continues to expand.
Where Stable Cities Cluster
Stable cities are distributed across the U.S., with no strong regional pattern. The largest cluster is in mid-density Midwest and Mid-Atlantic metros where the post-industrial pollution drop largely played out before the EPA AQS reporting window we use began.
Among the 430 stable cities tracked here, the largest concentrations are in TX (22), OH (21), FL (20), VA (18), NC (18). The dominant pollutant in these cities is Ozone (235 cities), followed by PM2.5 (183), PM10 (12).
All Stable Cities
Frequently Asked Questions
A city qualifies as "stable" when its 10-year linear regression on annual median AQI shows a slope between -0.1 and +0.1 AQI points per year — neither measurably improving nor worsening over the period. Stability is a useful baseline: residents can plan around what they know about local air without expecting major changes from year to year. But stability can mean either of two very different things — a clean city that is not eroding, or a polluted city that is not improving.
430 of 1,020 monitored US cities currently show stable air quality trends based on 10-year EPA data — 42.2% of all tracked areas.
Stable air quality usually reflects a balance: emission reductions from cleaner vehicles and power plants are being offset by population growth, traffic increases, or periodic wildfire-smoke events. Cities that have been "average pollution" for decades tend to stay that way unless something changes — a major refinery closes, a new freight hub opens, or wildfire smoke becomes a regular summer fixture. Stability is also more common in mid-density, mid-population cities without major recent industrial change.
Stability can break in either direction. Watch for new industrial development, freight corridors, or port expansions that could push a stable-clean city toward worsening. Watch for vehicle fleet turnover, transit investment, or upwind power-plant retirements that could push a stable-polluted city toward improving. Watch for changing wildfire patterns: a stable Western city today may show worsening trends within a few years if wildfire activity continues to expand.
Trend is calculated using a linear regression of annual median AQI values over the most recent 10 years of data. Cities with a slope below -0.1 AQI/year are classified as Improving, above +0.1 as Worsening, and between as Stable. Using a 10-year window smooths out year-to-year volatility from weather events and isolates the underlying signal.
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Source: EPA Outdoor Air Quality Data, 2026.