Data / Median Air Quality Index (US EPA) / Washington County

Median Air Quality Index (US EPA) in Washington County

Median Air Quality Index (US EPA) in Washington County was 36 in 2025, according to the U.S. Environmental Protection Agency. That is up 3 from 2024.

2025, index36
Change on 2024+3
Series high422004
Series low282006

Next release: Tuesday, 13 July 2027, estimated by Invokely from past publication dates (low confidence), not announced by the publisher. Release calendar

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Median Air Quality Index (US EPA) in Washington County, 1999 to 2025

253035404519992003200720112015201920251999: 29 index2000: 40 index2001: 38 index2002: 38 index2003: 34 index2004: 42 index2005: 33 index2006: 28 index2007: 30 index2008: 33 index2009: 40 index2010: 33 index2011: 35 index2012: 37 index2013: 36 index2014: 35 index2015: 40 index2016: 35 index2017: 37 index2018: 36 index2019: 37 index2020: 34 index2021: 36 index2022: 37 index2023: 36 index2024: 33 index2025: 36 index253035404519992008201720251999: 29 index2000: 40 index2001: 38 index2002: 38 index2003: 34 index2004: 42 index2005: 33 index2006: 28 index2007: 30 index2008: 33 index2009: 40 index2010: 33 index2011: 35 index2012: 37 index2013: 36 index2014: 35 index2015: 40 index2016: 35 index2017: 37 index2018: 36 index2019: 37 index2020: 34 index2021: 36 index2022: 37 index2023: 36 index2024: 33 index2025: 36 index
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12, published 2026-07-13.
All 27 values
Periodindex
202536
202433
202336
202237
202136
202034
201937
201836
201737
201635
201540
201435
201336
201237
201135
201033
200940
200833
200730
200628
200533
200442
200334
200238
200138
200040
199929

Washington County compared with nearby places

Baker County: 29 indexClackamas County: 31 indexColumbia County: 27 indexCrook County: 28 indexDeschutes County: 23 indexGrant County: 37 indexHarney County: 28 indexJackson County: 43 indexJefferson County: 28 indexJosephine County: 33 indexKlamath County: 38 indexLake County: 26 indexLane County: 46 indexLinn County: 27 indexMarion County: 35 indexMultnomah County: 37 indexUmatilla County: 41 indexUnion County: 27 indexWallowa County: 26 indexWasco County: 25 indexWashington County: 36 index
  • Under 27
  • 27 to 28
  • 28 to 33
  • 33 to 37
  • 37 and over
  • No data
Median Air Quality Index (US EPA), 2025, index. Washington County is outlined. Same source and period for every area shown. Source: U.S. Environmental Protection Agency. Boundaries: U.S. Census Bureau cartographic boundary files.

Rankings

Definition

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

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How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Median Air Quality Index (US EPA), Washington County, 1999 to 2025) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Washington County, 1999 to 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/median-air-quality-index/washington-county-oregon. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Median Air Quality Index (US EPA), Washington County, 1999 to 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/median-air-quality-index/washington-county-oregon.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Washington County, 1999 to 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/median-air-quality-index/washington-county-oregon (Accessed: 12 October 2026).

BibTeX
@misc{environmental_median_air_quality_index_2025,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Washington County, 1999 to 2025}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/washington-county-oregon. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Washington County, 1999 to 2025
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/en/median-air-quality-index/washington-county-oregon
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/washington-county-oregon.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

What is the median Air Quality Index (US EPA) in Washington County?

Median Air Quality Index (US EPA) in Washington County was 36 in 2025, according to the U.S. Environmental Protection Agency. That is up 3 from 2024.

Where does this figure come from?

U.S. Environmental Protection Agency. EPA AirData annual AQI by county: median daily AQI. Retrieved by Invokely on 2026-10-12.

What was the highest median Air Quality Index (US EPA) in Washington County?

42 in 2004, the highest value since 1999 in this series.

Related statistics for Washington County

All statistics for Washington County | Washington County in figures