Data / Rankings / Share of days with good air quality (US EPA AQI) / Counties in Oregon

Counties in Oregon by share of days with good air quality (US EPA AQI)

Columbia County had the highest share of days with good air quality (US EPA AQI) of 23 counties in 2018, at 90.9%. Klamath County had the lowest, at 51.1%. The median was 74.5%. Source: EPA.

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Highest90.9Columbia County
Lowest51.1Klamath County
Median74.523 counties

Map of counties, 2018

Baker County: 78.7 %Benton County: 86.5 %Clackamas County: 82.1 %Columbia County: 90.9 %Crook County: 69.1 %Deschutes County: 75.2 %Douglas County: 76.2 %Grant County: 56.9 %Harney County: 60.8 %Jackson County: 52.2 %Jefferson County: 52.2 %Josephine County: 53.7 %Klamath County: 51.1 %Lake County: 68.2 %Lane County: 58.4 %Linn County: 69.6 %Marion County: 75.1 %Multnomah County: 74.5 %Umatilla County: 77.2 %Union County: 77.9 %Wallowa County: 76.3 %Wasco County: 76.6 %Washington County: 71.2 %
  • Under 58
  • 58 to 70
  • 70 to 75
  • 75 to 78
  • 78 and over
  • No data
%, 2018. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2018

Columbia County: 90.9 %Columbia County90.9Benton County: 86.5 %Benton County86.5Clackamas County: 82.1 %Clackamas County82.1Baker County: 78.7 %Baker County78.7Union County: 77.9 %Union County77.9Umatilla County: 77.2 %Umatilla County77.2Wasco County: 76.6 %Wasco County76.6Wallowa County: 76.3 %Wallowa County76.3Douglas County: 76.2 %Douglas County76.2Deschutes County: 75.2 %Deschutes County75.2Marion County: 75.1 %Marion County75.1Multnomah County: 74.5 %Multnomah County74.5Washington County: 71.2 %Washington County71.2Linn County: 69.6 %Linn County69.6Crook County: 69.1 %Crook County69.1Lake County: 68.2 %Lake County68.2Harney County: 60.8 %Harney County60.8Lane County: 58.4 %Lane County58.4Grant County: 56.9 %Grant County56.9Josephine County: 53.7 %Josephine County53.7Jackson County: 52.2 %Jackson County52.2Jefferson County: 52.2 %Jefferson County52.2Klamath County: 51.1 %Klamath County51.1Columbia County: 90.9 %Columbia County90.9Benton County: 86.5 %Benton County86.5Clackamas County: 82.1 %Clackamas County82.1Baker County: 78.7 %Baker County78.7Union County: 77.9 %Union County77.9Umatilla County: 77.2 %Umatilla County77.2Wasco County: 76.6 %Wasco County76.6Wallowa County: 76.3 %Wallowa County76.3Douglas County: 76.2 %Douglas County76.2Deschutes County: 75.2 %Deschutes County75.2Marion County: 75.1 %Marion County75.1Multnomah County: 74.5 %Multnomah County74.5Washington County: 71.2 %Washington County71.2Linn County: 69.6 %Linn County69.6Crook County: 69.1 %Crook County69.1Lake County: 68.2 %Lake County68.2Harney County: 60.8 %Harney County60.8Lane County: 58.4 %Lane County58.4Grant County: 56.9 %Grant County56.9Josephine County: 53.7 %Josephine County53.7Jackson County: 52.2 %Jackson County52.2Jefferson County: 52.2 %Jefferson County52.2Klamath County: 51.1 %Klamath County51.1
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2018 (%)Change on 2017
1Columbia County90.9+2.5 pts
2Benton County86.5+4.1 pts
3Clackamas County82.1-0.3 pts
4Baker County78.7+3.9 pts
5Union County77.9+2 pts
6Umatilla County77.2+16.4 pts
7Wasco County76.6+8.2 pts
8Wallowa County76.3-0.5 pts
9Douglas County76.2+2.1 pts
10Deschutes County75.2-1.5 pts
11Marion County75.1-4.2 pts
12Multnomah County74.5-1.7 pts
13Washington County71.2+0.8 pts
14Linn County69.60 pts
15Crook County69.1+5 pts
16Lake County68.2-2.9 pts
17Harney County60.8+5.2 pts
18Lane County58.4+3.6 pts
19Grant County56.9-0.4 pts
20Josephine County53.7-6.3 pts
21Jackson County52.2-5.6 pts
21Jefferson County52.2-6.5 pts
23Klamath County51.1-8.5 pts

Other periods

About this ranking

Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.

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.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 3 counties with data in other periods have no value for 2018 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts (Counties in Oregon by share of days with good air quality (US EPA AQI), 2018) [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: good days as a share of days with an AQI, calculated with stored counts, Counties in Oregon by share of days with good air quality (US EPA AQI), 2018. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/good-air-quality-days-share/oregon-counties?period=2018. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Counties in Oregon by share of days with good air quality (US EPA AQI), 2018. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/good-air-quality-days-share/oregon-counties?period=2018.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts, Counties in Oregon by share of days with good air quality (US EPA AQI), 2018 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/good-air-quality-days-share/oregon-counties?period=2018 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_oregon_by_2018,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts: Counties in Oregon by share of days with good air quality (US EPA AQI), 2018}},
  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/rankings/good-air-quality-days-share/oregon-counties?period=2018. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. 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: good days as a share of days with an AQI, calculated with stored counts: Counties in Oregon by share of days with good air quality (US EPA AQI), 2018
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/rankings/good-air-quality-days-share/oregon-counties?period=2018
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/good-air-quality-days-share/oregon-counties?period=2018.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

Which county has the highest share of days with good air quality (US EPA AQI)?

Columbia County, with 90.9% in 2018, according to EPA.

Which county has the lowest share of days with good air quality (US EPA AQI)?

Klamath County, with 51.1% in 2018.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 3 counties have no value for 2018 and are not ranked.

Share of days with good air quality (US EPA AQI): other rankings

Counties in Oregon: more rankings