Median AQI
36
Good
Iowa · County air quality · 2025
Johnson County, Iowa
Median AQI 36 (Good). 71.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 36
- Median AQI
- 71.0%
- Good-air days
- 1
- Unhealthy days
- 33%
- Cleaner than US counties
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 36 with 71.0% of 304 monitored days in the Good band, driven mainly by PM2.5.
- 36
- median AQI · Good
- 71.0%
- 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.
Data updated July 2026
- Good · 216 d · 71.1%
- Moderate · 84 d · 27.6%
- USG · 3 d · 1.0%
- Unhealthy · 1 d · 0.3%
How did Johnson County's air break down in 2025?
Across 304 monitored days, 216 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). 304 days monitored. Median AQI: 36 (Good).
Insights: Johnson County, Iowa. EPA monitors recorded a median Air Quality Index of 36 across 304 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 216 (71%) fell in the Good band (AQI 0–50), 84 (28%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 62, while the worst single-day peak hit 159 (Unhealthy). Residents averaged about 21.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (304 days). Across the 2020–2025 trend window, good days shifted by +9 and the median AQI moved -11 points, placing the multi-year trajectory at improving. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Black Hawk (56.6% good, AQI 48); Bremer (87.1% good, AQI 38); Clinton (59.9% good, AQI 45); Harrison (83.0% good, AQI 39); Linn (61.2% good, AQI 44); Montgomery (68.8% good, AQI 43).
Air Quality Summary
Good Days
71.0%
216 of 304 monitored days
-4.0pp vs 75% target
Max AQI Recorded
159
Unhealthy
Health Grade
Moderate
90th-pct AQI 62
Johnson County, Good days share 71.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Johnson County, Unhealthy-or-worse share 0.3%
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 304 monitored days across EPA AQI categories.
Good
216
71%
Moderate
84
28%
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 · 304 days · 100.0%
Health Impact Assessment
Moderate
Johnson County's air quality is rated Moderate based on 71.0% 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 304 of 304 monitored days.
5-Year Air Quality Trend
Air quality is improving in Johnson County. Best year: 2024 (259 good 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 | 216 | 84 | 3 | 1 | 36 | 159 |
How does Johnson County compare?
How Johnson County compares
Good-day share worse than US avg
Johnson County 71.0%
Black Hawk County, Iowa 56.6%
US average 76.5%
Median AQI better than US avg
Johnson County 36
Black Hawk County, Iowa 48
US average 38
Unhealthy days / yr worse than US avg
Johnson County 1
Black Hawk County, Iowa 1
US average 0
Other Counties in Iowa
Air quality comparison for nearby counties in Iowa.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Johnson County.
Aroostook County, Maine
AQI 36 · 84.1% good
Berkeley County, South Carolina
AQI 36 · 92.2% good
Carter County, Kentucky
AQI 36 · 89.8% good
Claiborne County, Tennessee
AQI 36 · 96.3% good
Clark County, Illinois
AQI 36 · 92.1% good
Cobb County, Georgia
AQI 36 · 92.5% good
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 36 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 304 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Johnson County, Iowa? ▼
Johnson County has a median Air Quality Index (AQI) of 36, rated "Good." 71.0% of monitored days (216 out of 304) 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 304 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 based on 5-year trends (2020-2025). Best year: 2024 with 259 good days. Worst year: 2023 with 143 good days.
What does AQI 36 mean for health? ▼
Johnson County's median AQI of 36 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Johnson County compare to other counties in Iowa? ▼
Johnson County has 71.0% good air days. Nearby counties in Iowa: Black Hawk (56.6% good), Bremer (87.1% good), Clinton (59.9% good), Harrison (83.0% good), Linn (61.2% good), Montgomery (68.8% good).
What is the 90th percentile AQI in Johnson County? ▼
The 90th percentile AQI for Johnson County is 62, 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.
Every figure on PlainAir 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.