Median AQI
37
Good
Iowa · County air quality · 2025
Johnson County, Iowa
Median AQI 37 (Good). 70.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 70.1%
- Good-air days
- 1
- Unhealthy days
- 33%
- Cleaner than US counties
Johnson County's 2025 annual median AQI is 37 (Good), with 70.1% Good days
According to the U.S. EPA Air Quality System, Johnson County, Iowa posted a 2025 median AQI of 37 (Good) across 365 monitored days, with 70.1% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Johnson County's 70.1% Good-day share places it cleaner than 33% of US counties in 2025.
- Closest median-AQI peer
- Alachua County (88.7% Good, median AQI 37) is the closest nationwide median-AQI peer to Johnson County.
- 2020–2025 trend
- Johnson County's floor-qualifying Good-day share is improving from 2020 to 2025 (57.2% → 70.1%).
- Median AQI
- Median AQI: 37
The verdict
According to EPA Air Quality System monitoring data, Johnson County's air is good on balance, more polluted than the median US county, a median AQI of 37 with 70.1% of 365 monitored days in the Good band, driven mainly by PM2.5.
- 37
- median AQI · Good
- 70.1%
- days rated Good
- PM2.5
- main pollutant
- 33%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 159.
Annual release change
What changed in the 2025 EPA annual release
- Johnson County's peak single-day AQI rose from 83 to 159 between the 2024 and 2025 EPA annual releases, a change of +76 points.
- Johnson County's Unhealthy-category days rose from 0 to 1 between the 2024 and 2025 EPA annual releases, a change of +1 days.
Data updated August 2026
- Good · 256 d · 70.1%
- Moderate · 105 d · 28.8%
- USG · 3 d · 0.8%
- Unhealthy · 1 d · 0.3%
How did Johnson County's air break down in 2025?
Across 365 monitored days, 256 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 159 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 37 (Good).
Insights: Johnson County, Iowa. EPA monitors recorded a median Air Quality Index of 37 across 365 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 256 (70%) fell in the Good band (AQI 0–50), 105 (29%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 159 (Unhealthy). Residents averaged about 21.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (365 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +13.0 points and the median AQI moved -10 points, placing the multi-year trajectory at improving. The annual record contains 1 day at Unhealthy or worse. On that day, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Black Hawk (53.4% good, AQI 49); Bremer (87.1% good, AQI 38); Clinton (59.5% good, AQI 45); Harrison (83.0% good, AQI 39); Linn (61.4% good, AQI 44); Montgomery (69.3% good, AQI 43).
Air Quality Summary
Good Days
70.1%
256 of 365 monitored days
-4.9pp vs 75% target
Max AQI Recorded
159
Unhealthy
Health Grade
Moderate
90th-pct AQI 61
Johnson County, Good days share 70.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Johnson County, Unhealthy-or-worse share 2.7%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
256
70%
Moderate
105
29%
USG
3
1%
Unhealthy
1
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Johnson County.
- PM2.5 · 365 days · 100.0%
Health Impact Assessment
Moderate
Johnson County's air quality is rated Moderate based on 70.1% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 3 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 159. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 365 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Johnson County. Highest Good-day share: 2024 (70.8%, 259 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 207 | 154 | 1 | 0 | 47 | 105 |
| 2021 | 172 | 190 | 2 | 0 | 52 | 121 |
| 2022 | 223 | 141 | 1 | 0 | 44 | 108 |
| 2023 | 143 | 216 | 2 | 3 | 53 | 210 |
| 2024 | 259 | 107 | 0 | 0 | 39 | 83 |
| 2025 | 256 | 105 | 3 | 1 | 37 | 159 |
How does Johnson County compare?
How Johnson County compares
Good-day share worse than typical
Johnson County 70.1%
Alachua County, Florida 88.7%
Typical US county 76.0%
Median AQI better than typical
Johnson County 37
Alachua County, Florida 37
Typical US county 39
Unhealthy days / yr about typical
Johnson County 1
Alachua County, Florida 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Johnson County (37), not geographic neighbors.
Alachua County, Florida
Median AQI 37 · 88.7% Good-day share
Arlington County, Virginia
Median AQI 37 · 87.4% Good-day share
Bennington County, Vermont
Median AQI 37 · 83.6% Good-day share
Boone County, Missouri
Median AQI 37 · 93.2% Good-day share
Bradford County, Pennsylvania
Median AQI 37 · 81.6% Good-day share
Brown County, Wisconsin
Median AQI 37 · 73.2% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Hancock County, Mississippi
70.1% Good-day share · median AQI 43
Macomb County, Michigan
70.1% Good-day share · median AQI 40
Ramsey County, Minnesota
70.1% Good-day share · median AQI 34
Sangamon County, Illinois
70.1% Good-day share · median AQI 41
Tippecanoe County, Indiana
70.3% Good-day share · median AQI 39
Pottawattamie County, Iowa
70.3% Good-day share · median AQI 37
Iowa counties on the map
Geographic containment only, other monitored counties in Iowa, independent of AQI or pollutant match.
What Johnson County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 37 means for exposure. Health guidance
- See how Johnson County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Johnson County with its Iowa neighbours before drawing a conclusion about the region. All of Iowa
Based on 365 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Johnson County, Iowa? ▼
Johnson County has a median Air Quality Index (AQI) of 37, rated "Good." 70.1% of monitored days (256 out of 365) had good air quality in 2025.
What is the main pollutant in Johnson County? ▼
The primary pollutant in Johnson County is Fine Particles (PM2.5), which was the main AQI driver on 365 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Johnson County have? ▼
In 2025, Johnson County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 159.
Is the air quality in Johnson County getting better or worse? ▼
Air quality in Johnson County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 70.8% (259 of 366 days). Lowest qualifying Good-day share: 2023 at 39.3% (143 of 365 days).
What does AQI 37 mean for health? ▼
Johnson County's median AQI of 37 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Johnson County compare to other counties in Iowa? ▼
Johnson County has 70.1% good air days. Nearby counties in Iowa: Black Hawk (53.4% good), Bremer (87.1% good), Clinton (59.5% good), Harrison (83.0% good), Linn (61.4% good), Montgomery (69.3% good).
What is the 90th percentile AQI in Johnson County? ▼
The 90th percentile AQI for Johnson County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 159 (Unhealthy).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Johnson County, Iowa · 2020–2025
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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.