EnviroNearby

Snohomish County, Washington air quality history

Daily Air Quality Index summaries from EPA monitors in Snohomish, Washington, 1980–2025.

68%
Good days in 2025
41
Median daily AQI, 2025
1
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 Snohomish, Washington on 365 days. 248 of those days (68%) were in the Good range, and the median daily AQI was 41. That median is higher than the typical monitored county in Washington (median 28 across 30 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 365 days. Across the years with fuller monitoring, the share of Good days fell: an average of 95% in 1980–1982 versus 69% 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 125 of 125 days19801981: Good 162 of 167 days1981: Moderate 5 of 167 days1982: Good 224 of 257 days1982: Moderate 29 of 257 days1982: Unhealthy for Sensitive Groups 3 of 257 days1982: Unhealthy 1 of 257 days1983: Good 311 of 360 days1983: Moderate 48 of 360 days1983: Unhealthy for Sensitive Groups 1 of 360 days1984: Good 304 of 361 days1984: Moderate 57 of 361 days1985: Good 274 of 353 days1985: Moderate 73 of 353 days1985: Unhealthy for Sensitive Groups 6 of 353 days19851986: Good 289 of 335 days1986: Moderate 44 of 335 days1986: Unhealthy for Sensitive Groups 2 of 335 days1987: Good 131 of 287 days1987: Moderate 153 of 287 days1987: Unhealthy for Sensitive Groups 3 of 287 days1988: Good 168 of 366 days1988: Moderate 189 of 366 days1988: Unhealthy for Sensitive Groups 9 of 366 days1989: Good 142 of 359 days1989: Moderate 214 of 359 days1989: Unhealthy for Sensitive Groups 3 of 359 days1990: Good 143 of 349 days1990: Moderate 204 of 349 days1990: Unhealthy for Sensitive Groups 2 of 349 days19901991: Good 176 of 357 days1991: Moderate 180 of 357 days1991: Unhealthy for Sensitive Groups 1 of 357 days1992: Good 185 of 366 days1992: Moderate 181 of 366 days1993: Good 245 of 365 days1993: Moderate 119 of 365 days1993: Unhealthy for Sensitive Groups 1 of 365 days1994: Good 292 of 365 days1994: Moderate 72 of 365 days1994: Unhealthy for Sensitive Groups 1 of 365 days1995: Good 325 of 365 days1995: Moderate 39 of 365 days1995: Unhealthy for Sensitive Groups 1 of 365 days19951996: Good 346 of 366 days1996: Moderate 20 of 366 days1997: Good 355 of 365 days1997: Moderate 10 of 365 days1998: Good 263 of 279 days1998: Moderate 16 of 279 days1999: Good 308 of 365 days1999: Moderate 55 of 365 days1999: Unhealthy for Sensitive Groups 2 of 365 days2000: Good 173 of 366 days2000: Moderate 182 of 366 days2000: Unhealthy for Sensitive Groups 11 of 366 days20002001: Good 153 of 365 days2001: Moderate 206 of 365 days2001: Unhealthy for Sensitive Groups 6 of 365 days2002: Good 177 of 365 days2002: Moderate 181 of 365 days2002: Unhealthy for Sensitive Groups 7 of 365 days2003: Good 163 of 365 days2003: Moderate 192 of 365 days2003: Unhealthy for Sensitive Groups 10 of 365 days2004: Good 152 of 366 days2004: Moderate 207 of 366 days2004: Unhealthy for Sensitive Groups 7 of 366 days2005: Good 175 of 365 days2005: Moderate 180 of 365 days2005: Unhealthy for Sensitive Groups 9 of 365 days2005: Unhealthy 1 of 365 days20052006: Good 187 of 365 days2006: Moderate 172 of 365 days2006: Unhealthy for Sensitive Groups 6 of 365 days2007: Good 212 of 365 days2007: Moderate 140 of 365 days2007: Unhealthy for Sensitive Groups 11 of 365 days2007: Unhealthy 2 of 365 days2008: Good 199 of 366 days2008: Moderate 166 of 366 days2008: Unhealthy for Sensitive Groups 1 of 366 days2009: Good 186 of 365 days2009: Moderate 166 of 365 days2009: Unhealthy for Sensitive Groups 13 of 365 days2010: Good 266 of 363 days2010: Moderate 97 of 363 days20102011: Good 239 of 365 days2011: Moderate 118 of 365 days2011: Unhealthy for Sensitive Groups 8 of 365 days2012: Good 250 of 366 days2012: Moderate 114 of 366 days2012: Unhealthy for Sensitive Groups 1 of 366 days2012: Unhealthy 1 of 366 days2013: Good 227 of 365 days2013: Moderate 136 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 241 of 365 days2014: Moderate 120 of 365 days2014: Unhealthy for Sensitive Groups 4 of 365 days2015: Good 238 of 362 days2015: Moderate 112 of 362 days2015: Unhealthy for Sensitive Groups 10 of 362 days2015: Unhealthy 2 of 362 days20152016: Good 278 of 366 days2016: Moderate 85 of 366 days2016: Unhealthy for Sensitive Groups 3 of 366 days2017: Good 244 of 365 days2017: Moderate 105 of 365 days2017: Unhealthy for Sensitive Groups 13 of 365 days2017: Unhealthy 3 of 365 days2018: Good 260 of 365 days2018: Moderate 96 of 365 days2018: Unhealthy for Sensitive Groups 5 of 365 days2018: Unhealthy 4 of 365 days2019: Good 227 of 364 days2019: Moderate 136 of 364 days2019: Unhealthy for Sensitive Groups 1 of 364 days2020: Good 234 of 366 days2020: Moderate 122 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days2020: Unhealthy 3 of 366 days2020: Very Unhealthy 4 of 366 days20202021: Good 248 of 365 days2021: Moderate 114 of 365 days2021: Unhealthy for Sensitive Groups 3 of 365 days2022: Good 210 of 362 days2022: Moderate 129 of 362 days2022: Unhealthy for Sensitive Groups 13 of 362 days2022: Unhealthy 6 of 362 days2022: Very Unhealthy 3 of 362 days2022: Hazardous 1 of 362 days2023: Good 246 of 365 days2023: Moderate 116 of 365 days2023: Unhealthy for Sensitive Groups 2 of 365 days2023: Unhealthy 1 of 365 days2024: Good 262 of 366 days2024: Moderate 104 of 366 days2025: Good 248 of 365 days2025: Moderate 116 of 365 days2025: Unhealthy for Sensitive Groups 1 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 year0501001980: 90th percentile AQI 371981: 90th percentile AQI 431982: 90th percentile AQI 591983: 90th percentile AQI 541984: 90th percentile AQI 541985: 90th percentile AQI 621986: 90th percentile AQI 541987: 90th percentile AQI 771988: 90th percentile AQI 841989: 90th percentile AQI 791990: 90th percentile AQI 791991: 90th percentile AQI 731992: 90th percentile AQI 701993: 90th percentile AQI 611994: 90th percentile AQI 561995: 90th percentile AQI 511996: 90th percentile AQI 471997: 90th percentile AQI 441998: 90th percentile AQI 451999: 90th percentile AQI 572000: 90th percentile AQI 792001: 90th percentile AQI 742002: 90th percentile AQI 712003: 90th percentile AQI 832004: 90th percentile AQI 762005: 90th percentile AQI 792006: 90th percentile AQI 742007: 90th percentile AQI 792008: 90th percentile AQI 702009: 90th percentile AQI 792010: 90th percentile AQI 622011: 90th percentile AQI 702012: 90th percentile AQI 632013: 90th percentile AQI 742014: 90th percentile AQI 712015: 90th percentile AQI 692016: 90th percentile AQI 612017: 90th percentile AQI 842018: 90th percentile AQI 682019: 90th percentile AQI 712020: 90th percentile AQI 682021: 90th percentile AQI 632022: 90th percentile AQI 782023: 90th percentile AQI 642024: 90th percentile AQI 592025: 90th percentile AQI 611980: Median AQI 261981: Median AQI 251982: Median AQI 351983: Median AQI 321984: Median AQI 351985: Median AQI 381986: Median AQI 351987: Median AQI 541988: Median AQI 541989: Median AQI 551990: Median AQI 551991: Median AQI 511992: Median AQI 501993: Median AQI 421994: Median AQI 391995: Median AQI 361996: Median AQI 331997: Median AQI 271998: Median AQI 301999: Median AQI 322000: Median AQI 522001: Median AQI 532002: Median AQI 512003: Median AQI 522004: Median AQI 532005: Median AQI 512006: Median AQI 492007: Median AQI 472008: Median AQI 482009: Median AQI 492010: Median AQI 362011: Median AQI 412012: Median AQI 382013: Median AQI 382014: Median AQI 392015: Median AQI 382016: Median AQI 322017: Median AQI 332018: Median AQI 332019: Median AQI 402020: Median AQI 402021: Median AQI 352022: Median AQI 392023: Median AQI 382024: Median AQI 382025: Median AQI 411980198519901995200020052010201520202025
  • 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)365100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536524811610004161125PM2.5
20243662621040000385999PM2.5
202336524611621003864175PM2.5
2022362210129136313978362PM2.5
202136524811430003563137PM2.5
202036623412233404068250PM2.5
201936422713610004071114PM2.5
20183652609654003368186PM2.5
2017365244105133003384161PM2.5
20163662788530003261120PM2.5
2015362238112102003869158PM2.5
201436524112040003971133PM2.5
201336522713620003874115PM2.5
201236625011411003863157PM2.5
201136523911880004170147PM2.5
2010363266970000366287PM2.5
2009365186166130004979131PM2.5
200836619916610004870108PM2.5
2007365212140112004779162PM2.5
200636518717260004974147PM2.5
200536517518091005179156PM2.5
200436615220770005376131PM2.5
2003365163192100005283129PM2.5
200236517718170005171132PM2.5
200136515320660005374126PM2.5
2000366173182110005279129PM2.5
19993653085520003257148CO
1998279263160000304587CO
1997365355100000274474Ozone
1996366346200000334790CO
19953653253910003651105CO
19943652927210003956108CO
199336524511910004261101CO
19923661851810000507096CO
199135717618010005173113CO
199034914320420005579109CO
198935914221430005579133CO
198836616818990005484125CO
198728713115330005477109CO
19863352894420003554105CO
19853532747360003862140CO
1984361304570000355489CO
19833603114810003254101CO
19822572242931003559179Ozone
198116716250000254390Ozone
198012512500000263749Ozone

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 Washington with a similar median AQI in 2025

All monitored counties in Washington

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