Tennessee · County air quality · 2025
Hamilton County, Tennessee
Median AQI 44 (Good). 64.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 64.9%
- Good-air days
- 0
- Unhealthy days
- 23%
- Cleaner than US counties
Hamilton County's 2025 annual median AQI is 44 (Good), with 64.9% Good days
According to the U.S. EPA Air Quality System, Hamilton County, Tennessee posted a 2025 median AQI of 44 (Good) across 365 monitored days, with 64.9% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Hamilton County's 64.9% Good-day share places it cleaner than 23% of US counties in 2025.
- Closest median-AQI peer
- Allegan County (63.9% Good, median AQI 44) is the closest nationwide median-AQI peer to Hamilton County.
- 2020–2025 trend
- Hamilton County's floor-qualifying Good-day share is improving from 2020 to 2025 (60.2% → 64.9%).
- Median AQI
- Median AQI: 44
According to the 2025 EPA AQS county release on PlainAirData, Hamilton County, Tennessee ranks #680 of 951 by median AQI (44) and #733 by good-day share (64.9%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Annual release change
What changed in the 2025 EPA annual release
- Hamilton County's Good-day share rose from 54.4% to 64.9% between the 2024 and 2025 EPA annual releases, a change of +10.5 percentage points.
- Hamilton County's peak single-day AQI rose from 126 to 141 between the 2024 and 2025 EPA annual releases, a change of +15 points.
- Hamilton County's median AQI fell from 48 to 44 between the 2024 and 2025 EPA annual releases, a change of -4 points.
Data updated August 2026
- Good · 237 d · 64.9%
- Moderate · 126 d · 34.5%
- USG · 2 d · 0.5%
How did Hamilton County's air break down in 2025?
Across 365 monitored days, 237 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 →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Hamilton County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Hamilton County's Good-day share is 64.9% - cleaner than 23% of that comparison set.
Hamilton County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
64.9% 23rd percentile higher than 23% of 951 US counties
Each bar is a band; taller bars hold more US counties. 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
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Hamilton County.
- PM2.5 · 240 days · 65.8%
- Ozone · 125 days · 34.2%
2024 daily-monitor rhythm in Hamilton County
Month-by-month median AQI from EPA day-level county monitors (349 reported days in 2024). Aug posted the highest typical readings (median AQI 56, peak 115); Jan was cleanest at median 32. Summer months (Jun–Aug) averaged median AQI 53 vs 41 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,770 daily readings show a recurring local pattern: Jun has the highest matched-month median AQI (55), while Jan is lowest (41). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Hamilton County's air quality is rated Moderate based on 64.9% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 64.9% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 240 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Hamilton County. Highest Good-day share: 2025 (64.9%, 237 of 365 monitored 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 | 237 | 126 | 2 | 0 | 44 | 141 |
How does Hamilton County compare?
How Hamilton County compares
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 Hamilton County, Tennessee · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
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.