Counties Above the Federal Air-Quality Standard by ZIP Code

Data current as of June 2026 — recomputed by ZipCheckup from federal data each build.

As of June 2026, 171 of the 825 U.S. counties with an EPA air-quality monitor had a 2023-2025 design value above the federal standard for ground-level ozone or fine-particle pollution.

By state

We report two independent facts side by side and do not rank states. A larger count reflects the size of a state's inventory and its reporting activity, not a judgment about water safety.

How we compute this

We read the EPA's official design-value workbooks for ozone and fine particles and use the county-level tables, which carry each county's worst monitored 2023-2025 design value along with its FIPS code. A design value is the three-year statistic the EPA uses to judge attainment, so it is a steadier measure of chronic air quality than any single year. We flag a county when that value is above the standard: ozone above 0.070 parts per million, annual fine particles above 9.0 micrograms per cubic meter, or 24-hour fine particles above 35.

These are monitored design values, not official EPA nonattainment designations — the EPA sets those at the designated-area level, and an area can cover only part of a county. Of the 825 counties with a monitor for either pollutant, 171 were above a standard, spanning 52 states and jurisdictions.

Only about a thousand of the roughly 3,140 U.S. counties operate an air-quality monitor, so every figure here is a share of MONITORED counties, never of all counties. A county absent from the EPA's data is unmonitored, not confirmed to meet the standard — we omit it rather than record it as clean. Each monitored county maps to the ZIP codes within it.

Frequently asked questions

How many U.S. counties are above the federal air-quality standard?

Based on the EPA's 2023-2025 design values, 171 of the 825 counties with an air-quality monitor had a value above a National Ambient Air Quality Standard for ozone or fine particles, as of June 2026. That is 109 counties above the ozone standard and 91 above a fine-particle standard. Counties without a monitor are not counted, because their air is unmeasured rather than confirmed to meet the standard. according to ZipCheckup's reading of federal data as of June 2026.

What is an air-quality design value?

A design value is the three-year statistic the EPA uses to decide whether an area meets a National Ambient Air Quality Standard. For ground-level ozone the standard is 0.070 parts per million; for fine particles it is 9.0 micrograms per cubic meter as an annual average and 35 over a 24-hour period. ZipCheckup compares each monitored county's worst 2023-2025 design value to these standards, as of June 2026, and reports only monitored counties.