Median AQI
35
Good
Tennessee · County air quality · 2025
DeKalb County, Tennessee
Median AQI 35 (Good). 95.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 35
- Median AQI
- 95.4%
- Good-air days
- 0
- Unhealthy days
- 90%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, DeKalb County's air is good on balance, among the cleanest 10% of US counties, a median AQI of 35 with 95.4% of 237 monitored days in the Good band, driven mainly by Ozone.
- 35
- median AQI · Good
- 95.4%
- days rated Good
- Ozone
- main pollutant
- 90%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Data updated July 2026
- Good · 226 d · 95.4%
- Moderate · 11 d · 4.6%
How did DeKalb County's air break down in 2025?
Across 237 monitored days, 226 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 84 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 237 days monitored. Median AQI: 35 (Good).
Insights: DeKalb County, Tennessee. EPA monitors recorded a median Air Quality Index of 35 across 237 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 226 (95%) fell in the Good band (AQI 0–50), 11 (5%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 47, while the worst single-day peak hit 84 (Moderate). Residents averaged about 28.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (237 days). Across the 2020–2025 trend window, good days shifted by -110 and the median AQI moved +2 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 84, moderate 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); Dyer (79.4% good, AQI 34); Hamilton (64.1% good, AQI 45).
Air Quality Summary
Good Days
95.4%
226 of 237 monitored days
20.4pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Excellent
90th-pct AQI 47
DeKalb County, Good days share 95.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
DeKalb 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 237 monitored days across EPA AQI categories.
Good
226
95%
Moderate
11
5%
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 DeKalb County.
- Ozone · 237 days · 100.0%
Health Impact Assessment
Excellent
DeKalb County's air quality is rated Excellent based on 95.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 95.4% of monitored days in 2025, with a median AQI of 35. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 237 of 237 monitored days.
5-Year Air Quality Trend
Air quality is worsening in DeKalb County. Best year: 2021 (349 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 336 | 5 | 0 | 0 | 33 | 61 |
| 2021 | 349 | 14 | 0 | 0 | 35 | 84 |
| 2022 | 348 | 11 | 0 | 0 | 35 | 100 |
| 2023 | 333 | 19 | 0 | 0 | 37 | 90 |
| 2024 | 312 | 24 | 0 | 0 | 38 | 77 |
| 2025 | 226 | 11 | 0 | 0 | 35 | 84 |
How does DeKalb County compare?
How DeKalb County compares
Good-day share better than US avg
DeKalb County 95.4%
Anderson County, Tennessee 91.0%
US average 76.5%
Median AQI better than US avg
DeKalb County 35
Anderson County, Tennessee 42
US average 38
Unhealthy days / yr about average
DeKalb 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 DeKalb County.
Androscoggin County, Maine
AQI 35 · 85.5% good
Asotin County, Washington
AQI 35 · 73.8% good
Benton County, Washington
AQI 35 · 88.9% good
Benzie County, Michigan
AQI 35 · 91.1% good
Brooke County, West Virginia
AQI 35 · 79.3% good
Bucks County, Pennsylvania
AQI 35 · 87.5% good
What DeKalb 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 35 means for exposure. Health guidance
- See how DeKalb County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare DeKalb County with its Tennessee neighbours before drawing a conclusion about the region. All of Tennessee
Based on 237 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 DeKalb County, Tennessee? ▼
DeKalb County has a median Air Quality Index (AQI) of 35, rated "Good." 95.4% of monitored days (226 out of 237) had good air quality in 2025.
What is the main pollutant in DeKalb County? ▼
The primary pollutant in DeKalb County is Ozone (O3), which was the main AQI driver on 237 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does DeKalb County have? ▼
In 2025, DeKalb County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 84.
Is the air quality in DeKalb County getting better or worse? ▼
Air quality in DeKalb County is worsening based on 5-year trends (2020-2025). Best year: 2021 with 349 good days. Worst year: 2025 with 226 good days.
What does AQI 35 mean for health? ▼
DeKalb County's median AQI of 35 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 DeKalb County compare to other counties in Tennessee? ▼
DeKalb County has 95.4% good air days. Nearby counties in Tennessee: Anderson (91.0% good), Blount (69.6% good), Claiborne (96.3% good), Davidson (51.8% good), Dyer (79.4% good), Hamilton (64.1% good).
What is the 90th percentile AQI in DeKalb County? ▼
The 90th percentile AQI for DeKalb County is 47, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 84 (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.