Median AQI
39
Good
Kentucky · County air quality · 2025
Simpson County, Kentucky
Median AQI 39 (Good). 92.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 92.6%
- Good-air days
- 0
- Unhealthy days
- 82%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Simpson County's air is good on balance, cleaner than most US counties, a median AQI of 39 with 92.6% of 121 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 92.6%
- days rated Good
- Ozone
- main pollutant
- 82%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 74.
Data updated July 2026
- Good · 112 d · 92.6%
- Moderate · 9 d · 7.4%
How did Simpson County's air break down in 2025?
Across 121 monitored days, 112 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 74 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 121 days monitored. Median AQI: 39 (Good).
Insights: Simpson County, Kentucky. EPA monitors recorded a median Air Quality Index of 39 across 121 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 112 (93%) fell in the Good band (AQI 0–50), 9 (7%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 50, while the worst single-day peak hit 74 (Moderate). Residents averaged about 27.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (121 days). Across the 2020–2025 trend window, good days shifted by -105 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 74, moderate but never Unhealthy. Nearby counties show comparable readings: Bell (63.5% good, AQI 43); Boone (95.1% good, AQI 38); Boyd (82.8% good, AQI 39); Bullitt (92.7% good, AQI 39); Campbell (78.5% good, AQI 39); Carter (89.8% good, AQI 36).
Air Quality Summary
Good Days
92.6%
112 of 121 monitored days
17.6pp vs 75% target
Max AQI Recorded
74
Moderate
Health Grade
Excellent
90th-pct AQI 50
Simpson County, Good days share 92.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Simpson County, Unhealthy-or-worse share 0.0%
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 121 monitored days across EPA AQI categories.
Good
112
93%
Moderate
9
7%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Simpson County.
- Ozone · 121 days · 100.0%
Health Impact Assessment
Excellent
Simpson County's air quality is rated Excellent based on 92.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.6% of monitored days in 2025, with a median AQI of 39. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 121 of 121 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Simpson County. Best year: 2021 (222 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 217 | 4 | 0 | 0 | 36 | 67 |
| 2021 | 222 | 21 | 0 | 0 | 37 | 90 |
| 2022 | 217 | 24 | 0 | 0 | 39 | 93 |
| 2023 | 204 | 33 | 7 | 0 | 43 | 122 |
| 2024 | 204 | 38 | 0 | 0 | 43 | 97 |
| 2025 | 112 | 9 | 0 | 0 | 39 | 74 |
How does Simpson County compare?
How Simpson County compares
Good-day share better than US avg
Simpson County 92.6%
Bell County, Kentucky 63.5%
US average 76.5%
Median AQI worse than US avg
Simpson County 39
Bell County, Kentucky 43
US average 38
Unhealthy days / yr about average
Simpson County 0
Bell County, Kentucky 0
US average 0
Other Counties in Kentucky
Air quality comparison for nearby counties in Kentucky.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Simpson County.
Ada County, Idaho
AQI 39 · 80.6% good
Aiken County, South Carolina
AQI 39 · 89.1% good
Albany County, New York
AQI 39 · 67.4% good
Alexander County, North Carolina
AQI 39 · 92.4% good
Ashland County, Wisconsin
AQI 39 · 85.6% good
Bennington County, Vermont
AQI 39 · 82.9% good
What Simpson County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 39 means for exposure. Health guidance
- See how Simpson County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Simpson County with its Kentucky neighbours before drawing a conclusion about the region. All of Kentucky
Based on 121 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 Simpson County, Kentucky? ▼
Simpson County has a median Air Quality Index (AQI) of 39, rated "Good." 92.6% of monitored days (112 out of 121) had good air quality in 2025.
What is the main pollutant in Simpson County? ▼
The primary pollutant in Simpson County is Ozone (O3), which was the main AQI driver on 121 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Simpson County have? ▼
In 2025, Simpson County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 74.
Is the air quality in Simpson County getting better or worse? ▼
Air quality in Simpson County is worsening based on 5-year trends (2020-2025). Best year: 2021 with 222 good days. Worst year: 2025 with 112 good days.
What does AQI 39 mean for health? ▼
Simpson County's median AQI of 39 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 Simpson County compare to other counties in Kentucky? ▼
Simpson County has 92.6% good air days. Nearby counties in Kentucky: Bell (63.5% good), Boone (95.1% good), Boyd (82.8% good), Bullitt (92.7% good), Campbell (78.5% good), Carter (89.8% good).
What is the 90th percentile AQI in Simpson County? ▼
The 90th percentile AQI for Simpson County is 50, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 74 (Moderate).
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.