Median AQI
31
Good
South Dakota · County air quality · 2025
Pennington County, South Dakota
Median AQI 31 (Good). 79.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 31
- Median AQI
- 79.0%
- Good-air days
- 0
- Unhealthy days
- 49%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Pennington County's air is good on balance, more polluted than the median US county, a median AQI of 31 with 79.0% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 31
- median AQI · Good
- 79.0%
- days rated Good
- PM2.5
- main pollutant
- 49%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 107.
Data updated July 2026
- Good · 143 d · 79.0%
- Moderate · 37 d · 20.4%
- USG · 1 d · 0.6%
How did Pennington County's air break down in 2025?
Across 181 monitored days, 143 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 107 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 31 (Good).
Insights: Pennington County, South Dakota. EPA monitors recorded a median Air Quality Index of 31 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 143 (79%) fell in the Good band (AQI 0–50), 37 (20%) registered Moderate readings, and 1 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 60, while the worst single-day peak hit 107 (USG). Residents averaged about 23.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (118 days), PM10 (61 days), NO2 (2 days). Across the 2020–2025 trend window, good days shifted by -121 and the median AQI moved -4 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 107, usg but never Unhealthy. Nearby counties show comparable readings: Brookings (53.0% good, AQI 48); Brown (87.1% good, AQI 25); Clay (82.6% good, AQI 37); Codington (82.1% good, AQI 33); Custer (72.4% good, AQI 46); Hughes (94.4% good, AQI 14).
Air Quality Summary
Good Days
79.0%
143 of 181 monitored days
4.0pp vs 75% target
Max AQI Recorded
107
USG
Health Grade
Good
90th-pct AQI 60
Pennington County, Good days share 79.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Pennington 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
143
79%
Moderate
37
20%
USG
1
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 Pennington County.
- PM2.5 · 118 days · 65.2%
- PM10 · 61 days · 33.7%
- NO₂ · 2 days · 1.1%
Health Impact Assessment
Good
Pennington County's air quality is rated Good based on 79.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 79.0% of monitored days in 2025, with a median AQI of 31. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 118 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Pennington County. Best year: 2020 (264 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 264 | 102 | 0 | 0 | 35 | 92 |
| 2021 | 244 | 114 | 5 | 1 | 39 | 202 |
| 2022 | 238 | 123 | 2 | 0 | 40 | 116 |
| 2023 | 216 | 140 | 5 | 4 | 45 | 172 |
| 2024 | 248 | 114 | 4 | 0 | 36 | 111 |
| 2025 | 143 | 37 | 1 | 0 | 31 | 107 |
How does Pennington County compare?
How Pennington County compares
Good-day share better than US avg
Pennington County 79.0%
Brookings County, South Dakota 53.0%
US average 76.5%
Median AQI better than US avg
Pennington County 31
Brookings County, South Dakota 48
US average 38
Unhealthy days / yr about average
Pennington County 0
Brookings County, South Dakota 1
US average 0
Other Counties in South Dakota
Air quality comparison for nearby counties in South Dakota.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Pennington County.
Bannock County, Idaho
AQI 31 · 91.5% good
Clark County, Washington
AQI 31 · 89.3% good
Erie County, Pennsylvania
AQI 31 · 81.4% good
Honolulu County, Hawaii
AQI 31 · 95.0% good
Josephine County, Oregon
AQI 31 · 76.2% good
Monroe County, Wisconsin
AQI 31 · 75.2% good
What Pennington 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 31 means for exposure. Health guidance
- See how Pennington County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Pennington County with its South Dakota neighbours before drawing a conclusion about the region. All of South Dakota
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 Pennington County, South Dakota? ▼
Pennington County has a median Air Quality Index (AQI) of 31, rated "Good." 79.0% of monitored days (143 out of 181) had good air quality in 2025.
What is the main pollutant in Pennington County? ▼
The primary pollutant in Pennington County is Fine Particles (PM2.5), which was the main AQI driver on 118 days (65% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Pennington County have? ▼
In 2025, Pennington County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 107.
Is the air quality in Pennington County getting better or worse? ▼
Air quality in Pennington County is improving based on 5-year trends (2020-2025). Best year: 2020 with 264 good days. Worst year: 2025 with 143 good days.
What does AQI 31 mean for health? ▼
Pennington County's median AQI of 31 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 Pennington County compare to other counties in South Dakota? ▼
Pennington County has 79.0% good air days. Nearby counties in South Dakota: Brookings (53.0% good), Brown (87.1% good), Clay (82.6% good), Codington (82.1% good), Custer (72.4% good), Hughes (94.4% good).
What is the 90th percentile AQI in Pennington County? ▼
The 90th percentile AQI for Pennington County is 60, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 107 (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.