Median AQI
42
Good
Nebraska · County air quality · 2025
Sioux County, Nebraska
Median AQI 42 (Good). 87.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 87.4%
- Good-air days
- 0
- Unhealthy days
- 75%
- Cleaner than US counties
Sioux County's 2025 annual median AQI is 42 (Good), with 87.4% Good days
According to the U.S. EPA Air Quality System, Sioux County, Nebraska posted a 2025 median AQI of 42 (Good) across 214 monitored days, with 87.4% 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
- Sioux County's 87.4% Good-day share places it cleaner than 75% of US counties in 2025.
- Closest median-AQI peer
- Ada County (74.0% Good, median AQI 42) is the closest nationwide median-AQI peer to Sioux County.
- 2024–2025 trend
- Sioux County's floor-qualifying Good-day share is improving from 2024 to 2025 (79.6% → 87.4%).
- Median AQI
- Median AQI: 42
The verdict
According to EPA Air Quality System monitoring data, Sioux County's air is good on balance, cleaner than most US counties, a median AQI of 42 with 87.4% of 214 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 87.4%
- days rated Good
- Ozone
- main pollutant
- 75%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 100.
Annual release change
What changed in the 2025 EPA annual release
- Sioux County's Good-day share rose from 79.6% to 87.4% between the 2024 and 2025 EPA annual releases, a change of +7.8 percentage points.
- Sioux County's peak single-day AQI fell from 143 to 100 between the 2024 and 2025 EPA annual releases, a change of -43 points.
Data updated August 2026
- Good · 187 d · 87.4%
- Moderate · 27 d · 12.6%
How did Sioux County's air break down in 2025?
Across 214 monitored days, 187 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 100 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 214 days monitored. Median AQI: 42 (Good).
Insights: Sioux County, Nebraska. EPA monitors recorded a median Air Quality Index of 42 across 214 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 187 (87%) fell in the Good band (AQI 0–50), 27 (13%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 58, while the worst single-day peak hit 100 (Moderate). Residents averaged about 26.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (214 days). Across the 2024–2025 trend window, the share of monitored days rated Good shifted by +7.8 points (measured against 319 monitored days in 2024 and 214 in 2025, so raw day counts are not comparable) and the median AQI moved -2 points, placing the multi-year trajectory at improving. The worst single reading over the 2024–2025 window was AQI 100, moderate but never Unhealthy. Nearby counties show comparable readings: Cass (95.9% good, AQI 19); Douglas (71.0% good, AQI 42); Gage (75.8% good, AQI 34); Hall (82.5% good, AQI 34); Knox (92.0% good, AQI 36); Lancaster (85.4% good, AQI 37).
Air Quality Summary
Good Days
87.4%
187 of 214 monitored days
12.4pp vs 75% target
Max AQI Recorded
100
Moderate
Health Grade
Good
90th-pct AQI 58
Sioux County, Good days share 87.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Sioux 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 214 monitored days across EPA AQI categories.
Good
187
87%
Moderate
27
13%
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 Sioux County.
- Ozone · 214 days · 100.0%
Health Impact Assessment
Good
Sioux County's air quality is rated Good based on 87.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 87.4% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 214 of 214 monitored days.
5-Year Air Quality Trend
Air quality is improving in Sioux County. Highest Good-day share: 2025 (87.4%, 187 of 214 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2024 | 254 | 57 | 8 | 0 | 44 | 143 |
| 2025 | 187 | 27 | 0 | 0 | 42 | 100 |
How does Sioux County compare?
How Sioux County compares
Good-day share better than US avg
Sioux County 87.4%
Ada County, Idaho 74.0%
US average 76.0%
Median AQI worse than US avg
Sioux County 42
Ada County, Idaho 42
US average 39
Unhealthy days / yr better than US avg
Sioux County 0
Ada County, Idaho 0
US average 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Sioux County (42), not geographic neighbors.
Ada County, Idaho
Median AQI 42 · 74.0% Good-day share
Adams County, Pennsylvania
Median AQI 42 · 74.4% Good-day share
Allen County, Ohio
Median AQI 42 · 67.0% Good-day share
Asotin County, Washington
Median AQI 42 · 61.9% Good-day share
Baldwin County, Alabama
Median AQI 42 · 75.5% Good-day share
Bell County, Kentucky
Median AQI 42 · 67.0% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Amador County, California
87.4% Good-day share · median AQI 38
Arlington County, Virginia
87.4% Good-day share · median AQI 37
Warrick County, Indiana
87.4% Good-day share · median AQI 37
Lorain County, Ohio
87.3% Good-day share · median AQI 39
Manitowoc County, Wisconsin
87.4% Good-day share · median AQI 36
Custer County, Montana
87.2% Good-day share · median AQI 40
Nebraska counties on the map
Geographic containment only, other monitored counties in Nebraska, independent of AQI or pollutant match.
What Sioux 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 42 means for exposure. Health guidance
- See how Sioux County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Sioux County with its Nebraska neighbours before drawing a conclusion about the region. All of Nebraska
Based on 214 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Sioux County, Nebraska? ▼
Sioux County has a median Air Quality Index (AQI) of 42, rated "Good." 87.4% of monitored days (187 out of 214) had good air quality in 2025.
What is the main pollutant in Sioux County? ▼
The primary pollutant in Sioux County is Ozone (O3), which was the main AQI driver on 214 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Sioux County have? ▼
In 2025, Sioux County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 100.
Is the air quality in Sioux County getting better or worse? ▼
Air quality in Sioux County is improving across floor-qualifying years (2024-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 87.4% (187 of 214 days). Lowest qualifying Good-day share: 2024 at 79.6% (254 of 319 days).
What does AQI 42 mean for health? ▼
Sioux County's median AQI of 42 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Sioux County compare to other counties in Nebraska? ▼
Sioux County has 87.4% good air days. Nearby counties in Nebraska: Cass (95.9% good), Douglas (71.0% good), Gage (75.8% good), Hall (82.5% good), Knox (92.0% good), Lancaster (85.4% good).
What is the 90th percentile AQI in Sioux County? ▼
The 90th percentile AQI for Sioux County is 58, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 100 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Sioux County, Nebraska · 2020–2025
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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.