Median AQI
44
Good
Indiana · County air quality · 2025
Delaware County, Indiana
Median AQI 44 (Good). 63.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 63.4%
- Good-air days
- 0
- Unhealthy days
- 20%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Delaware County's air is good on balance, among the more polluted 10% of US counties, a median AQI of 44 with 63.4% of 273 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 63.4%
- days rated Good
- Ozone
- main pollutant
- 20%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 108.
Data updated July 2026
- Good · 173 d · 63.4%
- Moderate · 98 d · 35.9%
- USG · 2 d · 0.7%
How did Delaware County's air break down in 2025?
Across 273 monitored days, 173 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 108 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 44 (Good).
Insights: Delaware County, Indiana. EPA monitors recorded a median Air Quality Index of 44 across 273 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 173 (63%) fell in the Good band (AQI 0–50), 98 (36%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 65, while the worst single-day peak hit 108 (USG). Residents averaged about 19.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (142 days), PM2.5 (131 days). Across the 2020–2025 trend window, good days shifted by -130 and the median AQI moved +9 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 108, usg but never Unhealthy. Nearby counties show comparable readings: Allen (58.2% good, AQI 45); Bartholomew (69.2% good, AQI 44); Boone (86.9% good, AQI 38); Brown (94.5% good, AQI 37); Carroll (87.8% good, AQI 37); Clark (59.7% good, AQI 46).
Air Quality Summary
Good Days
63.4%
173 of 273 monitored days
-11.6pp vs 75% target
Max AQI Recorded
108
USG
Health Grade
Moderate
90th-pct AQI 65
Delaware County, Good days share 63.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Delaware 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 273 monitored days across EPA AQI categories.
Good
173
63%
Moderate
98
36%
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 Delaware County.
- Ozone · 142 days · 52.0%
- PM2.5 · 131 days · 48.0%
Health Impact Assessment
Moderate
Delaware County's air quality is rated Moderate based on 63.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 63.4% 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 Ozone, driving AQI on 142 of 273 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Delaware County. Best year: 2022 (303 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 303 | 62 | 0 | 0 | 35 | 97 |
| 2021 | 299 | 63 | 0 | 0 | 37 | 97 |
| 2022 | 303 | 55 | 1 | 0 | 38 | 115 |
| 2023 | 287 | 71 | 5 | 0 | 40 | 121 |
| 2024 | 240 | 126 | 0 | 0 | 44 | 97 |
| 2025 | 173 | 98 | 2 | 0 | 44 | 108 |
How does Delaware County compare?
How Delaware County compares
Good-day share worse than US avg
Delaware County 63.4%
Allen County, Indiana 58.2%
US average 76.5%
Median AQI worse than US avg
Delaware County 44
Allen County, Indiana 45
US average 38
Unhealthy days / yr about average
Delaware County 0
Allen County, Indiana 0
US average 0
Other Counties in Indiana
Air quality comparison for nearby counties in Indiana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Delaware County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Delaware 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 44 means for exposure. Health guidance
- See how Delaware County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Delaware County with its Indiana neighbours before drawing a conclusion about the region. All of Indiana
Based on 273 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 Delaware County, Indiana? ▼
Delaware County has a median Air Quality Index (AQI) of 44, rated "Good." 63.4% of monitored days (173 out of 273) had good air quality in 2025.
What is the main pollutant in Delaware County? ▼
The primary pollutant in Delaware County is Ozone (O3), which was the main AQI driver on 142 days (52% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Delaware County have? ▼
In 2025, Delaware County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 108.
Is the air quality in Delaware County getting better or worse? ▼
Air quality in Delaware County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 303 good days. Worst year: 2025 with 173 good days.
What does AQI 44 mean for health? ▼
Delaware County's median AQI of 44 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 Delaware County compare to other counties in Indiana? ▼
Delaware County has 63.4% good air days. Nearby counties in Indiana: Allen (58.2% good), Bartholomew (69.2% good), Boone (86.9% good), Brown (94.5% good), Carroll (87.8% good), Clark (59.7% good).
What is the 90th percentile AQI in Delaware County? ▼
The 90th percentile AQI for Delaware County is 65, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 108 (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.