Indiana · County air quality · 2025
Spencer County, Indiana
Median AQI 39 (Good). 67.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 67.4%
- Good-air days
- 0
- Unhealthy days
- 27%
- Cleaner than US counties
Spencer County's 2025 annual median AQI is 39 (Good), with 67.4% Good days
According to the U.S. EPA Air Quality System, Spencer County, Indiana posted a 2025 median AQI of 39 (Good) across 365 monitored days, with 67.4% 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
- Spencer County's 67.4% Good-day share places it cleaner than 27% of US counties in 2025.
- Closest median-AQI peer
- Aiken County (90.6% Good, median AQI 39) is the closest nationwide median-AQI peer to Spencer County.
- 2020–2025 trend
- Spencer County's floor-qualifying Good-day share is stable from 2020 to 2025 (65.6% → 67.4%).
- Median AQI
- Median AQI: 39
According to the 2025 EPA AQS county release on PlainAirData, Spencer County, Indiana ranks #392 of 951 by median AQI (39) and #696 by good-day share (67.4%). 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
- Spencer County's Good-day share fell from 78.1% to 67.4% between the 2024 and 2025 EPA annual releases, a change of -10.7 percentage points.
- Spencer County's peak single-day AQI rose from 68 to 88 between the 2024 and 2025 EPA annual releases, a change of +20 points.
- Spencer County's median AQI rose from 34 to 39 between the 2024 and 2025 EPA annual releases, a change of +5 points.
Data updated August 2026
- Good · 246 d · 67.4%
- Moderate · 119 d · 32.6%
How did Spencer County's air break down in 2025?
Across 365 monitored days, 246 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 88 (Moderate).
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 Spencer County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Spencer County's Good-day share is 67.4% - cleaner than 27% of that comparison set.
Spencer County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
67.4% 27th percentile higher than 27% 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 Spencer County.
- PM2.5 · 365 days · 100.0%
2024 daily-monitor rhythm in Spencer County
Month-by-month median AQI from EPA day-level county monitors (169 reported days in 2024). Aug posted the highest typical readings (median AQI 52, peak 62); Apr was cleanest at median 22. Summer months (Jun–Aug) averaged median AQI 47 vs 35 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–2024642 daily readings show a recurring local pattern: Jul has the highest matched-month median AQI (50), while Apr is lowest (33). 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
Spencer County's air quality is rated Moderate based on 67.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 67.4% 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 PM2.5, driving AQI on 365 of 365 monitored days.
5-Year Air Quality Trend
Air quality is stable in Spencer County. Highest Good-day share: 2024 (78.1%, 132 of 169 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 80 | 42 | 0 | 0 | 42 | 67 |
| 2021 | 78 | 42 | 0 | 0 | 42 | 89 |
| 2022 | 75 | 36 | 0 | 0 | 42 | 79 |
| 2023 | 80 | 39 | 0 | 1 | 43 | 170 |
| 2024 | 132 | 37 | 0 | 0 | 34 | 68 |
| 2025 | 246 | 119 | 0 | 0 | 39 | 88 |
How does Spencer County compare?
How Spencer 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 Spencer County, Indiana · 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.