Median AQI
45
Good
Tennessee · County air quality · 2025
Hamilton County, Tennessee
Median AQI 45 (Good). 64.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 45
- Median AQI
- 64.1%
- Good-air days
- 0
- Unhealthy days
- 21%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Hamilton County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 45 with 64.1% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 45
- median AQI · Good
- 64.1%
- days rated Good
- PM2.5
- main pollutant
- 21%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 141.
Data updated July 2026
- Good · 116 d · 64.1%
- Moderate · 63 d · 34.8%
- USG · 2 d · 1.1%
How did Hamilton County's air break down in 2025?
Across 181 monitored days, 116 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 141 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 45 (Good).
Insights: Hamilton County, Tennessee. EPA monitors recorded a median Air Quality Index of 45 across 181 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 116 (64%) fell in the Good band (AQI 0–50), 63 (35%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 141 (USG). Residents averaged about 19.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (124 days), Ozone (57 days). Across the 2020–2025 trend window, good days shifted by -103 and the median AQI moved -1 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 141, usg but never Unhealthy. Nearby counties show comparable readings: Anderson (91.0% good, AQI 42); Blount (69.6% good, AQI 46); Claiborne (96.3% good, AQI 36); Davidson (51.8% good, AQI 50); DeKalb (95.4% good, AQI 35); Dyer (79.4% good, AQI 34).
Air Quality Summary
Good Days
64.1%
116 of 181 monitored days
-10.9pp vs 75% target
Max AQI Recorded
141
USG
Health Grade
Moderate
90th-pct AQI 61
Hamilton County, Good days share 64.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hamilton 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 181 monitored days across EPA AQI categories.
Good
116
64%
Moderate
63
35%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Hamilton County.
- PM2.5 · 124 days · 68.5%
- Ozone · 57 days · 31.5%
Health Impact Assessment
Moderate
Hamilton County's air quality is rated Moderate based on 64.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 64.1% of monitored days in 2025, with a median AQI of 45. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 124 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Hamilton County. Best year: 2020 (219 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 219 | 144 | 0 | 1 | 46 | 151 |
| 2021 | 191 | 159 | 1 | 0 | 48 | 101 |
| 2022 | 169 | 171 | 1 | 0 | 51 | 105 |
| 2023 | 175 | 187 | 3 | 0 | 51 | 137 |
| 2024 | 190 | 156 | 3 | 0 | 48 | 126 |
| 2025 | 116 | 63 | 2 | 0 | 45 | 141 |
How does Hamilton County compare?
How Hamilton County compares
Good-day share worse than US avg
Hamilton County 64.1%
Anderson County, Tennessee 91.0%
US average 76.5%
Median AQI worse than US avg
Hamilton County 45
Anderson County, Tennessee 42
US average 38
Unhealthy days / yr about average
Hamilton County 0
Anderson County, Tennessee 0
US average 0
Other Counties in Tennessee
Air quality comparison for nearby counties in Tennessee.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Hamilton County.
Adair County, Oklahoma
AQI 45 · 59.2% good
Allen County, Indiana
AQI 45 · 58.2% good
Atascosa County, Texas
AQI 45 · 58.0% good
Baker County, Florida
AQI 45 · 69.1% good
Carson City County, Nevada
AQI 45 · 79.3% good
Clinton County, Iowa
AQI 45 · 59.9% good
What Hamilton County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 45 means for exposure. Health guidance
- See how Hamilton County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Hamilton County with its Tennessee neighbours before drawing a conclusion about the region. All of Tennessee
Based on 181 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 Hamilton County, Tennessee? ▼
Hamilton County has a median Air Quality Index (AQI) of 45, rated "Good." 64.1% of monitored days (116 out of 181) had good air quality in 2025.
What is the main pollutant in Hamilton County? ▼
The primary pollutant in Hamilton County is Fine Particles (PM2.5), which was the main AQI driver on 124 days (69% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Hamilton County have? ▼
In 2025, Hamilton County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 141.
Is the air quality in Hamilton County getting better or worse? ▼
Air quality in Hamilton County is improving based on 5-year trends (2020-2025). Best year: 2020 with 219 good days. Worst year: 2025 with 116 good days.
What does AQI 45 mean for health? ▼
Hamilton County's median AQI of 45 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 Hamilton County compare to other counties in Tennessee? ▼
Hamilton County has 64.1% good air days. Nearby counties in Tennessee: Anderson (91.0% good), Blount (69.6% good), Claiborne (96.3% good), Davidson (51.8% good), DeKalb (95.4% good), Dyer (79.4% good).
What is the 90th percentile AQI in Hamilton County? ▼
The 90th percentile AQI for Hamilton County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 141 (USG).
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.