EnviroNearby

Jefferson County, Washington air quality history

Daily Air Quality Index summaries from EPA monitors in Jefferson, Washington, 1992–2025.

97%
Good days in 2025
20
Median daily AQI, 2025
0
Days above 100 in 2025
335
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Jefferson, Washington on 335 days. 326 of those days (97%) were in the Good range, and the median daily AQI was 20. That median is lower than the typical monitored county in Washington (median 28 across 30 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 335 days. Across the years with fuller monitoring, the share of Good days rose: an average of 78% in 2003–2005 versus 97% in 2023–2025.

Years with fewer than 120 monitored days (1992, 2000, 2001, 2002) 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%1992: Good 16 of 16 days19922000: Good 38 of 59 days2000: Moderate 20 of 59 days2000: Unhealthy for Sensitive Groups 1 of 59 days2001: Good 8 of 15 days2001: Moderate 7 of 15 days20012002: Good 38 of 92 days2002: Moderate 54 of 92 days2003: Good 284 of 365 days2003: Moderate 81 of 365 days20032004: Good 290 of 366 days2004: Moderate 76 of 366 days2005: Good 283 of 365 days2005: Moderate 82 of 365 days20052006: Good 273 of 320 days2006: Moderate 47 of 320 days2007: Good 295 of 362 days2007: Moderate 67 of 362 days20072008: Good 297 of 366 days2008: Moderate 69 of 366 days2009: Good 288 of 364 days2009: Moderate 76 of 364 days20092010: Good 329 of 355 days2010: Moderate 26 of 355 days2011: Good 331 of 363 days2011: Moderate 32 of 363 days20112012: Good 333 of 347 days2012: Moderate 14 of 347 days2013: Good 320 of 362 days2013: Moderate 42 of 362 days20132014: Good 302 of 342 days2014: Moderate 40 of 342 days2015: Good 275 of 307 days2015: Moderate 32 of 307 days20152016: Good 336 of 348 days2016: Moderate 12 of 348 days2017: Good 328 of 365 days2017: Moderate 36 of 365 days2017: Unhealthy for Sensitive Groups 1 of 365 days20172018: Good 327 of 359 days2018: Moderate 26 of 359 days2018: Unhealthy for Sensitive Groups 3 of 359 days2018: Unhealthy 3 of 359 days2019: Good 344 of 365 days2019: Moderate 21 of 365 days20192020: Good 321 of 340 days2020: Moderate 11 of 340 days2020: Unhealthy for Sensitive Groups 2 of 340 days2020: Unhealthy 2 of 340 days2020: Very Unhealthy 4 of 340 days2021: Good 352 of 358 days2021: Moderate 6 of 358 days20212022: Good 327 of 349 days2022: Moderate 22 of 349 days2023: Good 336 of 350 days2023: Moderate 14 of 350 days20232024: Good 300 of 311 days2024: Moderate 11 of 311 days2025: Good 326 of 335 days2025: Moderate 9 of 335 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 year0501001992: 90th percentile AQI 312000: 90th percentile AQI 652001: 90th percentile AQI 592002: 90th percentile AQI 832003: 90th percentile AQI 612004: 90th percentile AQI 562005: 90th percentile AQI 562006: 90th percentile AQI 532007: 90th percentile AQI 572008: 90th percentile AQI 572009: 90th percentile AQI 572010: 90th percentile AQI 442011: 90th percentile AQI 482012: 90th percentile AQI 392013: 90th percentile AQI 522014: 90th percentile AQI 522015: 90th percentile AQI 512016: 90th percentile AQI 392017: 90th percentile AQI 512018: 90th percentile AQI 482019: 90th percentile AQI 422020: 90th percentile AQI 432021: 90th percentile AQI 322022: 90th percentile AQI 412023: 90th percentile AQI 392024: 90th percentile AQI 352025: 90th percentile AQI 361992: Median AQI 212000: Median AQI 392001: Median AQI 492002: Median AQI 542003: Median AQI 322004: Median AQI 342005: Median AQI 342006: Median AQI 332007: Median AQI 292008: Median AQI 322009: Median AQI 332010: Median AQI 242011: Median AQI 252012: Median AQI 242013: Median AQI 282014: Median AQI 272015: Median AQI 262016: Median AQI 242017: Median AQI 242018: Median AQI 252019: Median AQI 262020: Median AQI 232021: Median AQI 202022: Median AQI 212023: Median AQI 212024: Median AQI 212025: Median AQI 2019922001200320052007200920112013201520172019202120232025
  • 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)335100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202533532690000203659PM2.5
2024311300110000213557PM2.5
2023350336140000213988PM2.5
2022349327220000214190PM2.5
202135835260000203279PM2.5
20203403211122402343232PM2.5
2019365344210000264257PM2.5
20183593272633002548184PM2.5
20173653283610002451108PM2.5
2016348336120000243965PM2.5
2015307275320000265175PM2.5
2014342302400000275268PM2.5
2013362320420000285268PM2.5
2012347333140000243963PM2.5
2011363331320000254865PM2.5
2010355329260000244466PM2.5
2009364288760000335774PM2.5
2008366297690000325784PM2.5
2007362295670000295775PM2.5
2006320273470000335371PM2.5
2005365283820000345683PM2.5
2004366290760000345682PM2.5
2003365284810000326190PM2.5
20029238540000548392PM2.5
200115870000495966PM2.5
200059382010003965106PM2.5
1992161600000213133PM10

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 1992–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem