EnviroNearby

Cass County, Minnesota air quality history

Daily Air Quality Index summaries from EPA monitors in Cass, Minnesota, 2003–2025.

83%
Good days in 2025
28
Median daily AQI, 2025
13
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 Cass, Minnesota on 364 days. 301 of those days (83%) were in the Good range, and the median daily AQI was 28. That median is lower than the typical monitored county in Minnesota (median 37 across 21 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 364 days. Across the years with fuller monitoring, the share of Good days fell: an average of 89% in 2018–2020 versus 81% in 2023–2025.

Years with fewer than 120 monitored days (2007, 2008, 2009, 2010, 2011, 2012…) 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%2003: Good 45 of 55 days2003: Moderate 10 of 55 days20032004: Good 46 of 59 days2004: Moderate 13 of 59 days2005: Good 46 of 54 days2005: Moderate 8 of 54 days20052006: Good 47 of 59 days2006: Moderate 12 of 59 days2007: Good 48 of 52 days2007: Moderate 3 of 52 days2007: Unhealthy for Sensitive Groups 1 of 52 days20072008: Good 42 of 47 days2008: Moderate 5 of 47 days2009: Good 13 of 14 days2009: Moderate 1 of 14 days20092010: Good 27 of 27 days2011: Good 33 of 37 days2011: Moderate 4 of 37 days20112012: Good 17 of 20 days2012: Moderate 3 of 20 days2018: Good 268 of 320 days2018: Moderate 52 of 320 days20182019: Good 321 of 350 days2019: Moderate 28 of 350 days2019: Unhealthy for Sensitive Groups 1 of 350 days2020: Good 316 of 346 days2020: Moderate 30 of 346 days20202021: Good 103 of 352 days2021: Moderate 237 of 352 days2021: Unhealthy for Sensitive Groups 7 of 352 days2021: Unhealthy 4 of 352 days2021: Very Unhealthy 1 of 352 days2022: Good 309 of 348 days2022: Moderate 39 of 348 days20222023: Good 260 of 359 days2023: Moderate 94 of 359 days2023: Unhealthy for Sensitive Groups 5 of 359 days2024: Good 313 of 362 days2024: Moderate 48 of 362 days2024: Unhealthy 1 of 362 days20242025: Good 301 of 364 days2025: Moderate 50 of 364 days2025: Unhealthy for Sensitive Groups 5 of 364 days2025: Unhealthy 8 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 year0501002003: 90th percentile AQI 542004: 90th percentile AQI 582005: 90th percentile AQI 552006: 90th percentile AQI 582007: 90th percentile AQI 492008: 90th percentile AQI 522009: 90th percentile AQI 472010: 90th percentile AQI 442011: 90th percentile AQI 532012: 90th percentile AQI 552018: 90th percentile AQI 552019: 90th percentile AQI 442020: 90th percentile AQI 462021: 90th percentile AQI 692022: 90th percentile AQI 522023: 90th percentile AQI 642024: 90th percentile AQI 542025: 90th percentile AQI 592003: Median AQI 322004: Median AQI 312005: Median AQI 222006: Median AQI 272007: Median AQI 242008: Median AQI 212009: Median AQI 272010: Median AQI 222011: Median AQI 222012: Median AQI 222018: Median AQI 312019: Median AQI 182020: Median AQI 222021: Median AQI 542022: Median AQI 322023: Median AQI 322024: Median AQI 272025: Median AQI 282003200520072009201120182020202220242025
  • 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
Fine particles (PM2.5)364100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253643015058002859177PM2.5
20243623134801002754164PM2.5
20233592609450003264145PM2.5
2022348309390000325264PM2.5
202135210323774105469275PM2.5
2020346316300000224678PM2.5
20193503212810001844125PM2.5
20183202685200003155100PM2.5
2012201730000225564PM2.5
2011373340000225358PM2.5
2010272700000224450PM2.5
2009141310000274773PM2.5
2008474250000215287PM2.5
20075248310002449102PM2.5
20065947120000275879PM2.5
2005544680000225576PM2.5
20045946130000315882PM2.5
20035545100000325474PM2.5

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 Minnesota with a similar median AQI in 2025

All monitored counties in Minnesota

Source: U.S. EPA AirData, “Annual AQI by County” files for 2003–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem