Median AQI
39
Good
Wyoming · County air quality · 2024
Big Horn County, Wyoming
Median AQI 39 (Good). 89.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 89.2%
- Good-air days
- 0
- Unhealthy days
- 73%
- Cleaner than US counties
Big Horn County's 2024 annual median AQI is 39 (Good), with 89.2% Good days
According to the U.S. EPA Air Quality System, Big Horn County, Wyoming posted a 2024 median AQI of 39 (Good) across 353 monitored days, with 89.2% 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
- Big Horn County's 89.2% Good-day share places it cleaner than 73% of US counties in 2024.
- Closest median-AQI peer
- Chattooga County (96.3% Good, median AQI 39) is the closest nationwide median-AQI peer to Big Horn County.
- 2020–2024 trend
- Big Horn County's floor-qualifying Good-day share is worsening from 2020 to 2024 (97.2% → 89.2%).
- Median AQI
- Median AQI: 39
The verdict
According to EPA Air Quality System monitoring data, Big Horn County's air is good on balance, cleaner than the median US county, a median AQI of 39 with 89.2% of 353 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 89.2%
- days rated Good
- Ozone
- main pollutant
- 73%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 119.
Annual release change
What changed in the 2024 EPA annual release
- Big Horn County's peak single-day AQI rose from 77 to 119 between the 2023 and 2024 EPA annual releases, a change of +42 points.
- Big Horn County's Good-day share fell from 93.3% to 89.2% between the 2023 and 2024 EPA annual releases, a change of -4.1 percentage points.
Data updated August 2026
- Good · 315 d · 89.2%
- Moderate · 36 d · 10.2%
- USG · 2 d · 0.6%
How did Big Horn County's air break down in 2024?
Across 353 monitored days, 315 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 119 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2024). 353 days monitored. Median AQI: 39 (Good).
Insights: Big Horn County, Wyoming. EPA monitors recorded a median Air Quality Index of 39 across 353 measured days in 2024, earning a Good classification and a Good health grade. Of those days, 315 (89%) fell in the Good band (AQI 0–50), 36 (10%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 51, while the worst single-day peak hit 119 (USG). Residents averaged about 26.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (353 days). Across the 2020–2024 trend window, the share of monitored days rated Good shifted by -8.0 points and the median AQI moved +1 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2024 window was AQI 119, usg but never Unhealthy. Nearby counties show comparable readings: Albany (55.6% good, AQI 49); Campbell (74.3% good, AQI 44); Carbon (100.0% good, AQI 8); Converse (96.2% good, AQI 40); Fremont (69.6% good, AQI 47); Johnson (92.8% good, AQI 41).
Air Quality Summary
Good Days
89.2%
315 of 353 monitored days
14.2pp vs 75% target
Max AQI Recorded
119
USG
Health Grade
Good
90th-pct AQI 51
Big Horn County, Good days share 89.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Big Horn 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 (2024)
Distribution of 353 monitored days across EPA AQI categories.
Good
315
89%
Moderate
36
10%
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 Big Horn County.
- Ozone · 353 days · 100.0%
Health Impact Assessment
Good
Big Horn County's air quality is rated Good based on 89.2% good air days. No unhealthy air days were recorded in 2024.
Air quality was acceptable on 89.2% of monitored days in 2024, 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 Ozone, driving AQI on 353 of 353 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Big Horn County. Highest Good-day share: 2022 (98.3%, 356 of 362 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 349 | 8 | 2 | 0 | 38 | 126 |
| 2021 | 324 | 39 | 1 | 0 | 39 | 101 |
| 2022 | 356 | 6 | 0 | 0 | 38 | 64 |
| 2023 | 335 | 24 | 0 | 0 | 39 | 77 |
| 2024 | 315 | 36 | 2 | 0 | 39 | 119 |
How does Big Horn County compare?
How Big Horn County compares
Good-day share better than US avg
Big Horn County 89.2%
Chattooga County, Georgia 96.3%
US average 76.0%
Median AQI about average
Big Horn County 39
Chattooga County, Georgia 39
US average 39
Unhealthy days / yr better than US avg
Big Horn County 0
Chattooga County, Georgia 0
US average 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Big Horn County (39), not geographic neighbors.
Chattooga County, Georgia
Median AQI 39 · 96.3% Good-day share
Weston County, Wyoming
Median AQI 39 · 87.7% Good-day share
Sumter County, Georgia
Median AQI 38 · 93.4% Good-day share
Columbia County, Georgia
Median AQI 36 · 94.2% Good-day share
Jefferson County, Oklahoma
Median AQI 42 · 81.0% Good-day share
Pontotoc County, Oklahoma
Median AQI 43 · 71.6% 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).
Wyoming counties on the map
Geographic containment only, other monitored counties in Wyoming, independent of AQI or pollutant match.
What Big Horn 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 39 means for exposure. Health guidance
- See how Big Horn County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Big Horn County with its Wyoming neighbours before drawing a conclusion about the region. All of Wyoming
Based on 353 EPA-monitored days in 2024; 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 Big Horn County, Wyoming? ▼
Big Horn County has a median Air Quality Index (AQI) of 39, rated "Good." 89.2% of monitored days (315 out of 353) had good air quality in 2024.
What is the main pollutant in Big Horn County? ▼
The primary pollutant in Big Horn County is Ozone (O3), which was the main AQI driver on 353 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Big Horn County have? ▼
In 2024, Big Horn County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 119.
Is the air quality in Big Horn County getting better or worse? ▼
Air quality in Big Horn County is worsening across floor-qualifying years (2020-2024); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2022 at 98.3% (356 of 362 days). Lowest qualifying Good-day share: 2021 at 89.0% (324 of 364 days).
What does AQI 39 mean for health? ▼
Big Horn County's median AQI of 39 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Big Horn County compare to other counties in Wyoming? ▼
Big Horn County has 89.2% good air days. Nearby counties in Wyoming: Albany (55.6% good), Campbell (74.3% good), Carbon (100.0% good), Converse (96.2% good), Fremont (69.6% good), Johnson (92.8% good).
What is the 90th percentile AQI in Big Horn County? ▼
The 90th percentile AQI for Big Horn County is 51, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 119 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Big Horn County, Wyoming · 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.