State air quality · 2025
Iowa Air Quality Ranking
Across 15 monitored counties, the typical county in Iowa posts a median AQI of 42 (Good) and 66.8% of monitored days were rated Good, from EPA AQS.
- 42
- Avg median AQI
- 66.8%
- Good-air days
- 15
- Counties monitored
- 10%
- Cleaner than US states
Iowa's typical county median AQI is 42 (Good) across 15 monitored counties
According to the U.S. EPA Air Quality System, Iowa monitors 15 counties with a day-weighted Good-day share of 66.8%. Cleanest: Bremer County (87.1% Good). Most polluted: Black Hawk County (53.4%). These are annual summaries, not live AirNow readings.
Data source EPA Air Quality System (AQS)
- Cleaner than US states
- Iowa's day-weighted Good-day share of 66.8% places it cleaner than 10% of US states.
- In-state spread
- Within Iowa, Bremer County leads at 87.1% Good days while Black Hawk County sits at 53.4% across 15 monitored counties.
- 2024→2025 release
- Iowa's Good-day share moved -3.1 points vs the 2024 EPA annual release.
- Typical median AQI
- Typical median AQI: 42
Verify with AirNow → · EPA AQS →
EPA state monitoring brief
AQS state key IOWA
Iowa · 2025 EPA AQS · 15 counties · med AQI 42 · 66.8% Good · Bremer→Black Hawk spread
- GOOD 42 Median AQI · Good
- SHARE 66.8% Good-day share
- COUNT 15 Counties monitored
- UNH 7 Unhealthy+ days
- RANK 10% Cleaner than states
- PM25 64.9% Main pollutant share
Good-day share peers
Iowa's 66.8% Good-day share is cleaner than 10% of monitored US states; Bremer and Black Hawk County bracket the in-state range. Open Bremer County →
According to EPA AQS annual summaries on PlainAirData, Iowa ranks #46 of 52 by day-weighted good-day share (66.8%) and #43 by mean county median AQI (42.2). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).
Data updated August 2026
What changed, what drives it, and how thick is the sample
Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.
Release change
66.8%
Good-day share in 2025, down 3.1 percentage points vs 2024. County-mean median AQI 42, 0.8 points lower (cleaner) than 2024.
Pollutant mix
PM2.5
Main driver on 64.9% of pollutant-assigned days.
- PM2.5 64.9%
- Ozone 33.2%
- PM10 1.9%
Monitoring coverage
314
Average monitored days per county in the latest release. Every monitored county clears the 100-day ranking floor.
Counties Monitored
15
Good Days %
66.8%
Avg Median AQI
42
Total Unhealthy Days
7
Best Air Quality
Bremer County
Worst Air Quality
Black Hawk County
Where Iowa sits nationally
COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Iowa's day-weighted Good-day share is 66.8% - cleaner than 10% of that comparison set.
Iowa Good-day share vs. every US state
Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
66.8% 10th percentile higher than 10% of 52 US states
Each bar is a band; taller bars hold more US states. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Which counties in Iowa have the cleanest and most polluted air?
Cleanest counties in Iowa
| County | Good % | Median AQI | Max AQI | Unhealthy Days |
|---|---|---|---|---|
| Bremer | 87.1% | 38 | 115 | 0 |
| Harrison | 83.0% | 39 | 119 | 0 |
| Woodbury | 79.6% | 39 | 122 | 0 |
| Palo Alto | 72.3% | 40 | 134 | 0 |
| Pottawattamie | 70.3% | 37 | 87 | 0 |
| Johnson | 70.1% | 37 | 159 | 1 |
| Montgomery | 69.3% | 43 | 133 | 0 |
| Muscatine | 66.0% | 43 | 141 | 0 |
| Van Buren | 64.8% | 44 | 129 | 0 |
| Linn | 61.4% | 44 | 163 | 1 |
| Polk | 61.4% | 44 | 136 | 0 |
| Clinton | 59.5% | 45 | 166 | 1 |
| Webster | 59.2% | 45 | 165 | 2 |
| Scott | 58.9% | 46 | 159 | 1 |
| Black Hawk | 53.4% | 49 | 158 | 1 |
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.
Coverage: 15 counties in Iowa with active monitoring stations. Unmonitored counties are not represented.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025
Every figure on PlainAirData is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.