EnviroNearby

Missoula County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Missoula, Montana, 1980–2025.

82%
Good days in 2025
38
Median daily AQI, 2025
0
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Missoula, Montana on 365 days. 298 of those days (82%) were in the Good range, and the median daily AQI was 38. That median is higher than the typical monitored county in Montana (median 25.5 across 18 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 188 days. Across the years with fuller monitoring, the share of Good days rose: an average of 52% in 1980–1982 versus 63% in 2023–2025.

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%1980: Good 135 of 348 days1980: Moderate 190 of 348 days1980: Unhealthy for Sensitive Groups 18 of 348 days1980: Unhealthy 5 of 348 days19801981: Good 205 of 359 days1981: Moderate 142 of 359 days1981: Unhealthy for Sensitive Groups 8 of 359 days1981: Unhealthy 4 of 359 days1982: Good 158 of 257 days1982: Moderate 94 of 257 days1982: Unhealthy for Sensitive Groups 4 of 257 days1982: Unhealthy 1 of 257 days1983: Good 74 of 138 days1983: Moderate 57 of 138 days1983: Unhealthy for Sensitive Groups 5 of 138 days1983: Unhealthy 2 of 138 days1984: Good 306 of 351 days1984: Moderate 43 of 351 days1984: Unhealthy 2 of 351 days1985: Good 125 of 164 days1985: Moderate 33 of 164 days1985: Unhealthy for Sensitive Groups 5 of 164 days1985: Unhealthy 1 of 164 days19851986: Good 238 of 363 days1986: Moderate 112 of 363 days1986: Unhealthy for Sensitive Groups 13 of 363 days1987: Good 218 of 357 days1987: Moderate 127 of 357 days1987: Unhealthy for Sensitive Groups 11 of 357 days1987: Unhealthy 1 of 357 days1988: Good 189 of 366 days1988: Moderate 163 of 366 days1988: Unhealthy for Sensitive Groups 14 of 366 days1989: Good 233 of 365 days1989: Moderate 123 of 365 days1989: Unhealthy for Sensitive Groups 8 of 365 days1989: Unhealthy 1 of 365 days1990: Good 262 of 365 days1990: Moderate 102 of 365 days1990: Unhealthy for Sensitive Groups 1 of 365 days19901991: Good 254 of 365 days1991: Moderate 105 of 365 days1991: Unhealthy for Sensitive Groups 6 of 365 days1992: Good 241 of 334 days1992: Moderate 93 of 334 days1993: Good 268 of 364 days1993: Moderate 96 of 364 days1994: Good 305 of 365 days1994: Moderate 60 of 365 days1995: Good 326 of 365 days1995: Moderate 39 of 365 days19951996: Good 334 of 366 days1996: Moderate 32 of 366 days1997: Good 342 of 365 days1997: Moderate 23 of 365 days1998: Good 317 of 331 days1998: Moderate 14 of 331 days1999: Good 286 of 337 days1999: Moderate 50 of 337 days1999: Unhealthy 1 of 337 days2000: Good 299 of 366 days2000: Moderate 56 of 366 days2000: Unhealthy for Sensitive Groups 9 of 366 days2000: Unhealthy 1 of 366 days2000: Very Unhealthy 1 of 366 days20002001: Good 290 of 365 days2001: Moderate 70 of 365 days2001: Unhealthy for Sensitive Groups 5 of 365 days2002: Good 305 of 365 days2002: Moderate 60 of 365 days2003: Good 291 of 364 days2003: Moderate 63 of 364 days2003: Unhealthy for Sensitive Groups 6 of 364 days2003: Unhealthy 3 of 364 days2003: Very Unhealthy 1 of 364 days2004: Good 196 of 251 days2004: Moderate 50 of 251 days2004: Unhealthy for Sensitive Groups 3 of 251 days2004: Unhealthy 2 of 251 days2005: Good 276 of 342 days2005: Moderate 61 of 342 days2005: Unhealthy for Sensitive Groups 2 of 342 days2005: Unhealthy 3 of 342 days20052006: Good 282 of 359 days2006: Moderate 72 of 359 days2006: Unhealthy for Sensitive Groups 3 of 359 days2006: Unhealthy 2 of 359 days2007: Good 282 of 365 days2007: Moderate 77 of 365 days2007: Unhealthy for Sensitive Groups 5 of 365 days2007: Unhealthy 1 of 365 days2008: Good 269 of 352 days2008: Moderate 82 of 352 days2008: Unhealthy for Sensitive Groups 1 of 352 days2009: Good 211 of 364 days2009: Moderate 134 of 364 days2009: Unhealthy for Sensitive Groups 17 of 364 days2009: Unhealthy 2 of 364 days2010: Good 84 of 365 days2010: Moderate 234 of 365 days2010: Unhealthy for Sensitive Groups 40 of 365 days2010: Unhealthy 7 of 365 days20102011: Good 71 of 365 days2011: Moderate 237 of 365 days2011: Unhealthy for Sensitive Groups 49 of 365 days2011: Unhealthy 8 of 365 days2012: Good 54 of 366 days2012: Moderate 265 of 366 days2012: Unhealthy for Sensitive Groups 32 of 366 days2012: Unhealthy 15 of 366 days2013: Good 94 of 365 days2013: Moderate 247 of 365 days2013: Unhealthy for Sensitive Groups 18 of 365 days2013: Unhealthy 6 of 365 days2014: Good 173 of 365 days2014: Moderate 174 of 365 days2014: Unhealthy for Sensitive Groups 16 of 365 days2014: Unhealthy 2 of 365 days2015: Good 126 of 365 days2015: Moderate 216 of 365 days2015: Unhealthy for Sensitive Groups 14 of 365 days2015: Unhealthy 7 of 365 days2015: Very Unhealthy 2 of 365 days20152016: Good 72 of 366 days2016: Moderate 269 of 366 days2016: Unhealthy for Sensitive Groups 25 of 366 days2017: Good 52 of 365 days2017: Moderate 240 of 365 days2017: Unhealthy for Sensitive Groups 24 of 365 days2017: Unhealthy 14 of 365 days2017: Very Unhealthy 15 of 365 days2017: Hazardous 20 of 365 days2018: Good 146 of 365 days2018: Moderate 215 of 365 days2018: Unhealthy for Sensitive Groups 3 of 365 days2018: Unhealthy 1 of 365 days2019: Good 173 of 365 days2019: Moderate 188 of 365 days2019: Unhealthy for Sensitive Groups 3 of 365 days2019: Unhealthy 1 of 365 days2020: Good 155 of 366 days2020: Moderate 192 of 366 days2020: Unhealthy for Sensitive Groups 13 of 366 days2020: Unhealthy 6 of 366 days20202021: Good 122 of 365 days2021: Moderate 213 of 365 days2021: Unhealthy for Sensitive Groups 24 of 365 days2021: Unhealthy 6 of 365 days2022: Good 149 of 365 days2022: Moderate 201 of 365 days2022: Unhealthy for Sensitive Groups 11 of 365 days2022: Unhealthy 4 of 365 days2023: Good 156 of 364 days2023: Moderate 200 of 364 days2023: Unhealthy for Sensitive Groups 8 of 364 days2024: Good 237 of 366 days2024: Moderate 125 of 366 days2024: Unhealthy for Sensitive Groups 3 of 366 days2024: Unhealthy 1 of 366 days2025: Good 298 of 365 days2025: Moderate 67 of 365 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 year0501001502001980: 90th percentile AQI 921981: 90th percentile AQI 771982: 90th percentile AQI 771983: 90th percentile AQI 781984: 90th percentile AQI 541985: 90th percentile AQI 711986: 90th percentile AQI 811987: 90th percentile AQI 771988: 90th percentile AQI 791989: 90th percentile AQI 731990: 90th percentile AQI 671991: 90th percentile AQI 751992: 90th percentile AQI 631993: 90th percentile AQI 581994: 90th percentile AQI 551995: 90th percentile AQI 511996: 90th percentile AQI 491997: 90th percentile AQI 441998: 90th percentile AQI 401999: 90th percentile AQI 542000: 90th percentile AQI 662001: 90th percentile AQI 612002: 90th percentile AQI 552003: 90th percentile AQI 642004: 90th percentile AQI 622005: 90th percentile AQI 602006: 90th percentile AQI 612007: 90th percentile AQI 622008: 90th percentile AQI 612009: 90th percentile AQI 772010: 90th percentile AQI 1112011: 90th percentile AQI 1132012: 90th percentile AQI 1172013: 90th percentile AQI 902014: 90th percentile AQI 872015: 90th percentile AQI 922016: 90th percentile AQI 962017: 90th percentile AQI 1852018: 90th percentile AQI 802019: 90th percentile AQI 782020: 90th percentile AQI 852021: 90th percentile AQI 942022: 90th percentile AQI 812023: 90th percentile AQI 762024: 90th percentile AQI 682025: 90th percentile AQI 561980: Median AQI 541981: Median AQI 471982: Median AQI 441983: Median AQI 471984: Median AQI 101985: Median AQI 231986: Median AQI 441987: Median AQI 431988: Median AQI 491989: Median AQI 451990: Median AQI 351991: Median AQI 401992: Median AQI 411993: Median AQI 421994: Median AQI 361995: Median AQI 321996: Median AQI 301997: Median AQI 281998: Median AQI 251999: Median AQI 252000: Median AQI 252001: Median AQI 342002: Median AQI 332003: Median AQI 252004: Median AQI 272005: Median AQI 232006: Median AQI 272007: Median AQI 262008: Median AQI 262009: Median AQI 432010: Median AQI 612011: Median AQI 622012: Median AQI 652013: Median AQI 612014: Median AQI 522015: Median AQI 562016: Median AQI 582017: Median AQI 652018: Median AQI 542019: Median AQI 522020: Median AQI 542021: Median AQI 562022: Median AQI 542023: Median AQI 532024: Median AQI 432025: Median AQI 381980198519901995200020052010201520202025
  • 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)18852%
Ozone17748%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365298670000385698PM2.5
202436623712531004368153PM2.5
202336415620080005376134PM2.5
2022365149201114005481190PM2.5
2021365122213246005694162PM2.5
2020366155192136005485185PM2.5
201936517318831005278153PM2.5
201836514621531005480154PM2.5
20173655224024141520651851130PM2.5
201636672269250005896139PM2.5
2015365126216147205692209PM2.5
2014365173174162005287159PM2.5
201336594247186006190168PM2.5
20123665426532150065117188PM2.5
2011365712374980062113160PM2.5
2010365842344070061111192PM2.5
2009364211134172004377153PM2.5
20083522698210002661104PM2.5
20073652827751002662162PM10
20063592827232002761163PM10
20053422766123002360166PM10
20042511965032002762159PM2.5
20033642916363102564288PM2.5
2002365305600000335594Ozone
20013652907050003461132PM2.5
20003662995691102566254PM10
19993372865001002554175PM10
1998331317140000254086CO
1997365342230000284482CO
1996366334320000304989CO
1995365326390000325184CO
1994365305600000365581CO
1993364268960000425884CO
1992334241930000416398PM10
199136525410560004075125CO
199036526210210003567104PM10
198936523312381004573151CO
1988366189163140004979113CO
1987357218127111004377161CO
1986363238112130004481143PM10
19851641253351002371152CO
19843513064302001054165CO
1983138745752004778186CO
19822571589441004477195CO
198135920514284004777171CO
1980348135190185005492197CO

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 Montana with a similar median AQI in 2025

All monitored counties in Montana

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem