Median AQI
40
Good
North Dakota · County air quality · 2025
Billings County, North Dakota
Median AQI 40 (Good). 80.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 40
- Median AQI
- 80.3%
- Good-air days
- 4
- Unhealthy days
- 53%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Billings County's air is good on balance, cleaner than the median US county, a median AQI of 40 with 80.3% of 243 monitored days in the Good band, driven mainly by Ozone.
- 40
- median AQI · Good
- 80.3%
- days rated Good
- Ozone
- main pollutant
- 53%
- cleaner than US counties
4 days reached Unhealthy or worse; the worst single reading hit AQI 195.
Data updated July 2026
- Good · 195 d · 80.2%
- Moderate · 41 d · 16.9%
- USG · 3 d · 1.2%
- Unhealthy · 4 d · 1.6%
How did Billings County's air break down in 2025?
Across 243 monitored days, 195 fell in the Good band (AQI 0–50) and 4 reached Unhealthy or worse. The worst single day peaked at AQI 195 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 40 (Good).
Insights: Billings County, North Dakota. EPA monitors recorded a median Air Quality Index of 40 across 243 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 195 (80%) fell in the Good band (AQI 0–50), 41 (17%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 64, while the worst single-day peak hit 195 (Unhealthy). Residents averaged about 24.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (190 days), PM2.5 (53 days). Across the 2020–2025 trend window, good days shifted by -151 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. Residents and visitors experienced 4 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Burke (72.8% good, AQI 40); Burleigh (77.5% good, AQI 41); Cass (73.2% good, AQI 39); Dunn (78.6% good, AQI 40); McKenzie (79.0% good, AQI 41); Mercer (80.3% good, AQI 39).
Air Quality Summary
Good Days
80.3%
195 of 243 monitored days
5.3pp vs 75% target
Max AQI Recorded
195
Unhealthy
Health Grade
Good
90th-pct AQI 64
Billings County, Good days share 80.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Billings County, Unhealthy-or-worse share 1.6%
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 243 monitored days across EPA AQI categories.
Good
195
80%
Moderate
41
17%
USG
3
1%
Unhealthy
4
2%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Billings County.
- Ozone · 190 days · 78.2%
- PM2.5 · 53 days · 21.8%
Health Impact Assessment
Good
Billings County's air quality is rated Good based on 80.3% good air days. There were 4 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 3 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 195. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 190 of 243 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Billings County. Best year: 2020 (346 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 346 | 20 | 0 | 0 | 35 | 65 |
| 2021 | 299 | 60 | 3 | 2 | 37 | 161 |
| 2022 | 323 | 40 | 0 | 0 | 39 | 79 |
| 2023 | 282 | 73 | 7 | 2 | 39 | 226 |
| 2024 | 303 | 53 | 9 | 1 | 38 | 172 |
| 2025 | 195 | 41 | 3 | 4 | 40 | 195 |
How does Billings County compare?
How Billings County compares
Good-day share better than US avg
Billings County 80.3%
Burke County, North Dakota 72.8%
US average 76.5%
Median AQI worse than US avg
Billings County 40
Burke County, North Dakota 40
US average 38
Unhealthy days / yr worse than US avg
Billings County 4
Burke County, North Dakota 8
US average 0
Other Counties in North Dakota
Air quality comparison for nearby counties in North Dakota.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Billings County.
Amador County, California
AQI 40 · 84.8% good
Anne Arundel County, Maryland
AQI 40 · 87.2% good
Arlington County, Virginia
AQI 40 · 84.8% good
Bergen County, New Jersey
AQI 40 · 71.1% good
Berkeley County, West Virginia
AQI 40 · 81.1% good
Bossier County, Louisiana
AQI 40 · 86.5% good
What Billings County's air means for you
On most days the air here is fine, but Ozone drives 4 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 40 means for exposure. Health guidance
- See how Billings County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Billings County with its North Dakota neighbours before drawing a conclusion about the region. All of North Dakota
Based on 243 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 Billings County, North Dakota? ▼
Billings County has a median Air Quality Index (AQI) of 40, rated "Good." 80.3% of monitored days (195 out of 243) had good air quality in 2025.
What is the main pollutant in Billings County? ▼
The primary pollutant in Billings County is Ozone (O3), which was the main AQI driver on 190 days (78% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Billings County have? ▼
In 2025, Billings County recorded 4 unhealthy air days (4 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 195.
Is the air quality in Billings County getting better or worse? ▼
Air quality in Billings County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 346 good days. Worst year: 2025 with 195 good days.
What does AQI 40 mean for health? ▼
Billings County's median AQI of 40 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 Billings County compare to other counties in North Dakota? ▼
Billings County has 80.3% good air days. Nearby counties in North Dakota: Burke (72.8% good), Burleigh (77.5% good), Cass (73.2% good), Dunn (78.6% good), McKenzie (79.0% good), Mercer (80.3% good).
What is the 90th percentile AQI in Billings County? ▼
The 90th percentile AQI for Billings County is 64, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 195 (Unhealthy).
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.