Wasco County, Oregon air quality history

Daily Air Quality Index summaries from EPA monitors in Wasco, Oregon, 1986–2025.

86%

Good days in 2025

Median daily AQI, 2025

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 Wasco, Oregon on 365 days. 315 of those days (86%) were in the Good range, and the median daily AQI was 25. That median is lower than the typical monitored county in Oregon (median 29 across 21 counties), and lower than 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 rose: an average of 79% in 2004–2006 versus 86% in 2023–2025.

Years with fewer than 120 monitored days (1987, 1999, 2000, 2001, 2002, 2003…) 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.

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 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.

Pollutant	Days as main pollutant	Share of monitored days
Fine particles (PM2.5)	365	100%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Hazardous	Median AQI	90th pct.	Max AQI	Main pollutant
2025	365	315	50	0	0	0	0	25	54	81	PM2.5
2024	364	317	47	0	0	0	0	23	52	93	PM2.5
2023	289	244	40	2	2	1	0	27	55	214	PM2.5
2022	161	161	0	0	0	0	0	16	23	50	PM2.5
2021	319	287	30	1	1	0	0	22	51	163	PM2.5
2020	355	307	45	0	0	0	3	24	54	599	PM2.5
2019	350	262	88	0	0	0	0	31	62	89	PM2.5
2018	334	256	73	4	1	0	0	37	59	156	PM2.5
2017	364	249	99	7	8	1	0	39	72	278	PM2.5
2016	358	297	61	0	0	0	0	34	55	80	PM2.5
2015	358	300	56	0	2	0	0	27	55	158	PM2.5
2014	365	306	58	1	0	0	0	24	55	101	PM2.5
2013	361	275	82	3	1	0	0	35	58	183	PM2.5
2012	365	294	71	0	0	0	0	26	55	76	PM2.5
2011	365	313	52	0	0	0	0	23	55	87	PM2.5
2010	365	294	70	1	0	0	0	25	57	104	PM2.5
2009	365	277	88	0	0	0	0	30	58	83	PM2.5
2008	364	294	70	0	0	0	0	26	59	94	PM2.5
2007	362	277	85	0	0	0	0	28	63	95	PM2.5
2006	360	300	58	1	1	0	0	27	58	155	PM2.5
2005	360	279	81	0	0	0	0	26	62	99	PM2.5
2004	245	183	59	3	0	0	0	30	63	124	PM2.5
2003	52	41	11	0	0	0	0	30	57	75	PM2.5
2002	59	47	12	0	0	0	0	36	73	90	PM2.5
2001	61	48	12	1	0	0	0	32	57	117	PM2.5
2000	60	37	22	1	0	0	0	43	71	103	PM2.5
1999	3	3	0	0	0	0	0	46	49	49	PM2.5
1987	7	3	4	0	0	0	0	51	83	83	PM10
1986	48	42	6	0	0	0	0	31	56	78	PM10

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 Oregon with a similar median AQI in 2025

All monitored counties in Oregon

Source: U.S. EPA AirData, “Annual AQI by County” files for 1986–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem