EnviroNearby

King County, Washington air quality history

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

67%
Good days in 2025
43
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 King, Washington on 365 days. 245 of those days (67%) were in the Good range, and the median daily AQI was 43. That median is higher than the typical monitored county in Washington (median 28 across 30 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 217 days. Across the years with fuller monitoring, the share of Good days rose: an average of 21% in 1980–1982 versus 65% 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 82 of 366 days1980: Moderate 248 of 366 days1980: Unhealthy for Sensitive Groups 34 of 366 days1980: Unhealthy 2 of 366 days19801981: Good 69 of 365 days1981: Moderate 240 of 365 days1981: Unhealthy for Sensitive Groups 48 of 365 days1981: Unhealthy 5 of 365 days1981: Very Unhealthy 3 of 365 days1982: Good 78 of 365 days1982: Moderate 205 of 365 days1982: Unhealthy for Sensitive Groups 78 of 365 days1982: Unhealthy 4 of 365 days1983: Good 89 of 365 days1983: Moderate 257 of 365 days1983: Unhealthy for Sensitive Groups 15 of 365 days1983: Unhealthy 3 of 365 days1983: Very Unhealthy 1 of 365 days1984: Good 128 of 366 days1984: Moderate 232 of 366 days1984: Unhealthy for Sensitive Groups 6 of 366 days1985: Good 138 of 365 days1985: Moderate 199 of 365 days1985: Unhealthy for Sensitive Groups 25 of 365 days1985: Unhealthy 3 of 365 days19851986: Good 115 of 365 days1986: Moderate 226 of 365 days1986: Unhealthy for Sensitive Groups 21 of 365 days1986: Unhealthy 3 of 365 days1987: Good 124 of 365 days1987: Moderate 226 of 365 days1987: Unhealthy for Sensitive Groups 10 of 365 days1987: Unhealthy 4 of 365 days1987: Very Unhealthy 1 of 365 days1988: Good 202 of 366 days1988: Moderate 154 of 366 days1988: Unhealthy for Sensitive Groups 9 of 366 days1988: Unhealthy 1 of 366 days1989: Good 207 of 365 days1989: Moderate 147 of 365 days1989: Unhealthy for Sensitive Groups 11 of 365 days1990: Good 211 of 365 days1990: Moderate 136 of 365 days1990: Unhealthy for Sensitive Groups 11 of 365 days1990: Unhealthy 5 of 365 days1990: Very Unhealthy 2 of 365 days19901991: Good 216 of 365 days1991: Moderate 142 of 365 days1991: Unhealthy for Sensitive Groups 4 of 365 days1991: Unhealthy 3 of 365 days1992: Good 206 of 366 days1992: Moderate 144 of 366 days1992: Unhealthy for Sensitive Groups 12 of 366 days1992: Unhealthy 4 of 366 days1993: Good 249 of 365 days1993: Moderate 113 of 365 days1993: Unhealthy for Sensitive Groups 3 of 365 days1994: Good 295 of 365 days1994: Moderate 67 of 365 days1994: Unhealthy for Sensitive Groups 1 of 365 days1994: Very Unhealthy 2 of 365 days1995: Good 287 of 365 days1995: Moderate 71 of 365 days1995: Unhealthy for Sensitive Groups 7 of 365 days19951996: Good 278 of 366 days1996: Moderate 73 of 366 days1996: Unhealthy for Sensitive Groups 9 of 366 days1996: Unhealthy 6 of 366 days1997: Good 266 of 365 days1997: Moderate 94 of 365 days1997: Unhealthy for Sensitive Groups 4 of 365 days1997: Unhealthy 1 of 365 days1998: Good 288 of 365 days1998: Moderate 69 of 365 days1998: Unhealthy for Sensitive Groups 5 of 365 days1998: Unhealthy 1 of 365 days1998: Very Unhealthy 2 of 365 days1999: Good 139 of 365 days1999: Moderate 214 of 365 days1999: Unhealthy for Sensitive Groups 10 of 365 days1999: Unhealthy 2 of 365 days2000: Good 73 of 366 days2000: Moderate 274 of 366 days2000: Unhealthy for Sensitive Groups 18 of 366 days2000: Unhealthy 1 of 366 days20002001: Good 68 of 365 days2001: Moderate 283 of 365 days2001: Unhealthy for Sensitive Groups 13 of 365 days2001: Unhealthy 1 of 365 days2002: Good 110 of 365 days2002: Moderate 244 of 365 days2002: Unhealthy for Sensitive Groups 11 of 365 days2003: Good 96 of 365 days2003: Moderate 250 of 365 days2003: Unhealthy for Sensitive Groups 17 of 365 days2003: Unhealthy 2 of 365 days2004: Good 96 of 366 days2004: Moderate 254 of 366 days2004: Unhealthy for Sensitive Groups 14 of 366 days2004: Unhealthy 2 of 366 days2005: Good 86 of 365 days2005: Moderate 265 of 365 days2005: Unhealthy for Sensitive Groups 14 of 365 days20052006: Good 114 of 365 days2006: Moderate 231 of 365 days2006: Unhealthy for Sensitive Groups 13 of 365 days2006: Unhealthy 5 of 365 days2006: Very Unhealthy 2 of 365 days2007: Good 183 of 365 days2007: Moderate 174 of 365 days2007: Unhealthy for Sensitive Groups 7 of 365 days2007: Unhealthy 1 of 365 days2008: Good 171 of 366 days2008: Moderate 190 of 366 days2008: Unhealthy for Sensitive Groups 4 of 366 days2008: Unhealthy 1 of 366 days2009: Good 63 of 365 days2009: Moderate 291 of 365 days2009: Unhealthy for Sensitive Groups 10 of 365 days2009: Unhealthy 1 of 365 days2010: Good 221 of 365 days2010: Moderate 141 of 365 days2010: Unhealthy for Sensitive Groups 3 of 365 days20102011: Good 205 of 365 days2011: Moderate 160 of 365 days2012: Good 181 of 366 days2012: Moderate 178 of 366 days2012: Unhealthy for Sensitive Groups 7 of 366 days2013: Good 113 of 365 days2013: Moderate 246 of 365 days2013: Unhealthy for Sensitive Groups 6 of 365 days2014: Good 188 of 365 days2014: Moderate 174 of 365 days2014: Unhealthy for Sensitive Groups 3 of 365 days2015: Good 131 of 364 days2015: Moderate 224 of 364 days2015: Unhealthy for Sensitive Groups 9 of 364 days20152016: Good 240 of 366 days2016: Moderate 126 of 366 days2017: Good 194 of 365 days2017: Moderate 153 of 365 days2017: Unhealthy for Sensitive Groups 10 of 365 days2017: Unhealthy 7 of 365 days2017: Very Unhealthy 1 of 365 days2018: Good 212 of 365 days2018: Moderate 139 of 365 days2018: Unhealthy for Sensitive Groups 8 of 365 days2018: Unhealthy 4 of 365 days2018: Very Unhealthy 2 of 365 days2019: Good 208 of 365 days2019: Moderate 157 of 365 days2020: Good 248 of 366 days2020: Moderate 106 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days2020: Unhealthy 4 of 366 days2020: Very Unhealthy 5 of 366 days20202021: Good 248 of 365 days2021: Moderate 112 of 365 days2021: Unhealthy for Sensitive Groups 3 of 365 days2021: Unhealthy 2 of 365 days2022: Good 216 of 365 days2022: Moderate 130 of 365 days2022: Unhealthy for Sensitive Groups 14 of 365 days2022: Unhealthy 3 of 365 days2022: Very Unhealthy 2 of 365 days2023: Good 214 of 365 days2023: Moderate 145 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2023: Unhealthy 1 of 365 days2024: Good 255 of 366 days2024: Moderate 108 of 366 days2024: Unhealthy for Sensitive Groups 3 of 366 days2025: Good 245 of 365 days2025: Moderate 120 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 year0501001501980: 90th percentile AQI 1001981: 90th percentile AQI 1121982: 90th percentile AQI 1181983: 90th percentile AQI 871984: 90th percentile AQI 801985: 90th percentile AQI 921986: 90th percentile AQI 891987: 90th percentile AQI 861988: 90th percentile AQI 671989: 90th percentile AQI 741990: 90th percentile AQI 771991: 90th percentile AQI 761992: 90th percentile AQI 801993: 90th percentile AQI 641994: 90th percentile AQI 561995: 90th percentile AQI 621996: 90th percentile AQI 681997: 90th percentile AQI 651998: 90th percentile AQI 611999: 90th percentile AQI 752000: 90th percentile AQI 872001: 90th percentile AQI 822002: 90th percentile AQI 842003: 90th percentile AQI 902004: 90th percentile AQI 872005: 90th percentile AQI 802006: 90th percentile AQI 842007: 90th percentile AQI 792008: 90th percentile AQI 672009: 90th percentile AQI 782010: 90th percentile AQI 612011: 90th percentile AQI 662012: 90th percentile AQI 692013: 90th percentile AQI 752014: 90th percentile AQI 702015: 90th percentile AQI 732016: 90th percentile AQI 602017: 90th percentile AQI 772018: 90th percentile AQI 712019: 90th percentile AQI 642020: 90th percentile AQI 662021: 90th percentile AQI 602022: 90th percentile AQI 772023: 90th percentile AQI 632024: 90th percentile AQI 612025: 90th percentile AQI 611980: Median AQI 671981: Median AQI 661982: Median AQI 671983: Median AQI 601984: Median AQI 561985: Median AQI 571986: Median AQI 571987: Median AQI 561988: Median AQI 491989: Median AQI 491990: Median AQI 471991: Median AQI 471992: Median AQI 491993: Median AQI 441994: Median AQI 411995: Median AQI 401996: Median AQI 411997: Median AQI 421998: Median AQI 401999: Median AQI 542000: Median AQI 582001: Median AQI 562002: Median AQI 552003: Median AQI 552004: Median AQI 572005: Median AQI 562006: Median AQI 552007: Median AQI 502008: Median AQI 522009: Median AQI 582010: Median AQI 452011: Median AQI 482012: Median AQI 512013: Median AQI 552014: Median AQI 492015: Median AQI 532016: Median AQI 442017: Median AQI 482018: Median AQI 462019: Median AQI 482020: Median AQI 432021: Median AQI 432022: Median AQI 462023: Median AQI 462024: Median AQI 412025: Median AQI 431980198519901995200020052010201520202025
  • 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)21759%
Ozone13838%
Nitrogen dioxide (NO₂)103%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652451200000436197PM2.5
202436625510830004161119PM2.5
202336521414551004663165PM2.5
2022365216130143204677237PM2.5
202136524811232004360177PM2.5
202036624810634504366299PM2.5
20193652081570000486490PM2.5
201836521213984204671210PM2.5
2017365194153107104877227PM2.5
201636624012600004460100PM2.5
201536413122490005373129PM2.5
201436518817430004970150PM2.5
201336511324660005575149PM2.5
201236618117870005169140PM2.5
20113652051600000486699PM2.5
201036522114130004561122PM2.5
200936563291101005878162PM2.5
200836617119041005267164PM2.5
200736518317471005079159PM2.5
2006365114231135205584206PM2.5
200536586265140005680135PM2.5
200436696254142005787154PM2.5
200336596250172005590179PM2.5
2002365110244110005584143PM2.5
200136568283131005682161PM2.5
200036673274181005887151PM2.5
1999365139214102005475159PM2.5
19983652886951204061206CO
19973652669441004265166CO
19963662787396004168187CO
19953652877170004062143CO
19943652956710204156219CO
199336524911330004464115CO
1992366206144124004980172CO
199136521614243004776166CO
1990365211136115204777210CO
1989365207147110004974143CO
198836620215491004967187CO
1987365124226104105686208CO
1986365115226213005789195CO
1985365138199253005792173CO
198436612823260005680120CO
198336589257153106087202CO
1982365782057840067118176CO
1981365692404853066112220CO
1980366822483420067100168CO

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