EnviroNearby

Billings County, North Dakota air quality history

Daily Air Quality Index summaries from EPA monitors in Billings, North Dakota, 1986–2025.

83%
Good days in 2025
38
Median daily AQI, 2025
8
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Billings, North Dakota on 364 days. 301 of those days (83%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in North Dakota (median 38 across 9 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 275 days. Across the years with fuller monitoring, the share of Good days fell: an average of 96% in 1998–2000 versus 81% in 2023–2025.

Years with fewer than 120 monitored days (1986, 1987, 1988, 1989) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1986: Good 12 of 12 days19861987: Good 54 of 54 days1988: Good 61 of 61 days1989: Good 30 of 30 days1998: Good 130 of 133 days1998: Moderate 3 of 133 days1999: Good 343 of 358 days1999: Moderate 15 of 358 days19992000: Good 342 of 366 days2000: Moderate 24 of 366 days2001: Good 345 of 365 days2001: Moderate 20 of 365 days2002: Good 342 of 365 days2002: Moderate 23 of 365 days2003: Good 132 of 143 days2003: Moderate 11 of 143 days2004: Good 254 of 263 days2004: Moderate 9 of 263 days20042005: Good 333 of 352 days2005: Moderate 19 of 352 days2006: Good 308 of 364 days2006: Moderate 56 of 364 days2007: Good 327 of 358 days2007: Moderate 31 of 358 days2008: Good 337 of 366 days2008: Moderate 28 of 366 days2008: Unhealthy for Sensitive Groups 1 of 366 days2009: Good 351 of 360 days2009: Moderate 9 of 360 days20092010: Good 334 of 354 days2010: Moderate 20 of 354 days2011: Good 307 of 323 days2011: Moderate 16 of 323 days2012: Good 333 of 354 days2012: Moderate 21 of 354 days2013: Good 345 of 365 days2013: Moderate 20 of 365 days2014: Good 357 of 365 days2014: Moderate 8 of 365 days20142015: Good 303 of 365 days2015: Moderate 58 of 365 days2015: Unhealthy for Sensitive Groups 3 of 365 days2015: Unhealthy 1 of 365 days2016: Good 353 of 366 days2016: Moderate 13 of 366 days2017: Good 322 of 364 days2017: Moderate 40 of 364 days2017: Unhealthy for Sensitive Groups 1 of 364 days2017: Unhealthy 1 of 364 days2018: Good 311 of 361 days2018: Moderate 50 of 361 days2019: Good 346 of 365 days2019: Moderate 19 of 365 days20192020: Good 346 of 366 days2020: Moderate 20 of 366 days2021: Good 299 of 364 days2021: Moderate 60 of 364 days2021: Unhealthy for Sensitive Groups 3 of 364 days2021: Unhealthy 2 of 364 days2022: Good 323 of 363 days2022: Moderate 40 of 363 days2023: Good 282 of 365 days2023: Moderate 73 of 365 days2023: Unhealthy for Sensitive Groups 7 of 365 days2023: Unhealthy 2 of 365 days2023: Very Unhealthy 1 of 365 days2024: Good 303 of 366 days2024: Moderate 53 of 366 days2024: Unhealthy for Sensitive Groups 9 of 366 days2024: Unhealthy 1 of 366 days20242025: Good 301 of 364 days2025: Moderate 55 of 364 days2025: Unhealthy for Sensitive Groups 4 of 364 days2025: Unhealthy 4 of 364 days2025
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001986: 90th percentile AQI 201987: 90th percentile AQI 231988: 90th percentile AQI 191989: 90th percentile AQI 161998: 90th percentile AQI 461999: 90th percentile AQI 472000: 90th percentile AQI 482001: 90th percentile AQI 472002: 90th percentile AQI 482003: 90th percentile AQI 452004: 90th percentile AQI 452005: 90th percentile AQI 482006: 90th percentile AQI 582007: 90th percentile AQI 492008: 90th percentile AQI 492009: 90th percentile AQI 462010: 90th percentile AQI 482011: 90th percentile AQI 482012: 90th percentile AQI 482013: 90th percentile AQI 492014: 90th percentile AQI 452015: 90th percentile AQI 552016: 90th percentile AQI 452017: 90th percentile AQI 512018: 90th percentile AQI 542019: 90th percentile AQI 462020: 90th percentile AQI 462021: 90th percentile AQI 672022: 90th percentile AQI 512023: 90th percentile AQI 642024: 90th percentile AQI 602025: 90th percentile AQI 601986: Median AQI 141987: Median AQI 81988: Median AQI 91989: Median AQI 91998: Median AQI 311999: Median AQI 372000: Median AQI 362001: Median AQI 362002: Median AQI 352003: Median AQI 282004: Median AQI 312005: Median AQI 362006: Median AQI 382007: Median AQI 352008: Median AQI 372009: Median AQI 352010: Median AQI 382011: Median AQI 392012: Median AQI 352013: Median AQI 382014: Median AQI 362015: Median AQI 372016: Median AQI 352017: Median AQI 372018: Median AQI 382019: Median AQI 342020: Median AQI 352021: Median AQI 372022: Median AQI 392023: Median AQI 392024: Median AQI 382025: Median AQI 3819861999200420092014201920242025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Ozone27576%
Fine particles (PM2.5)8924%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253643015544003860195Ozone
20243663035391003860172Ozone
20233652827372103964226Ozone
2022363323400000395179Ozone
20213642996032003767161Ozone
2020366346200000354665Ozone
2019365346190000344684Ozone
2018361311500000385490Ozone
20173643224011003751156Ozone
2016366353130000354592Ozone
20153653035831003755154Ozone
201436535780000364563Ozone
2013365345200000384977Ozone
2012354333210000354867Ozone
2011323307160000394864Ozone
2010354334200000384890Ozone
200936035190000354671Ozone
20083663372810003749102Ozone
2007358327310000354997Ozone
20063643085600003858100Ozone
2005352333190000364874Ozone
200426325490000314576Ozone
2003143132110000284577PM2.5
2002365342230000354890Ozone
2001365345200000364767Ozone
2000366342240000364874Ozone
1999358343150000374777Ozone
199813313030000314658Ozone
198930300000091646PM10
198861610000091933PM10
198754540000082347PM10
1986121200000142031PM10

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in North Dakota with a similar median AQI in 2025

All monitored counties in North Dakota

Source: U.S. EPA AirData, “Annual AQI by County” files for 1986–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem