Union County, Oregon air quality history

Daily Air Quality Index summaries from EPA monitors in Union, Oregon, 1984–2025.

84%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

353

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Union, Oregon on 353 days. 298 of those days (84%) were in the Good range, and the median daily AQI was 27. That median is about the same as 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 352 days. Across the years with fuller monitoring, the share of Good days rose: an average of 79% in 1988–1990 versus 84% in 2023–2025.

Years with fewer than 120 monitored days (1984, 1985, 1986, 1987) 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)	352	100%
Coarse particles (PM10)	1	<1%

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	353	298	55	0	0	0	0	27	54	79	PM2.5
2024	366	303	61	2	0	0	0	23	59	128	PM2.5
2023	361	305	56	0	0	0	0	26	54	95	PM2.5
2022	361	283	74	4	0	0	0	28	57	130	PM2.5
2021	360	304	49	5	2	0	0	27	61	170	PM2.5
2020	366	300	57	1	4	3	1	27	56	326	PM2.5
2019	365	313	52	0	0	0	0	26	53	88	PM2.5
2018	362	282	74	5	1	0	0	32	59	192	PM2.5
2017	365	277	77	8	2	1	0	31	66	218	PM2.5
2016	364	297	67	0	0	0	0	24	56	99	PM2.5
2015	362	254	97	6	5	0	0	38	69	191	PM2.5
2014	363	255	102	6	0	0	0	34	75	140	PM2.5
2013	365	221	139	5	0	0	0	44	74	145	PM2.5
2012	365	260	103	2	0	0	0	34	62	147	PM2.5
2011	363	267	91	4	1	0	0	29	63	153	PM2.5
2010	365	261	103	1	0	0	0	33	61	106	PM2.5
2009	365	253	112	0	0	0	0	36	66	90	PM2.5
2008	365	249	116	0	0	0	0	39	62	87	PM2.5
2007	350	274	76	0	0	0	0	28	58	88	PM2.5
2006	364	236	117	10	1	0	0	38	69	187	PM2.5
2005	365	255	105	4	1	0	0	35	70	151	PM2.5
2004	365	263	101	1	0	0	0	33	61	104	PM2.5
2003	129	103	26	0	0	0	0	27	57	80	PM2.5
2002	343	262	79	2	0	0	0	31	60	118	PM2.5
2001	345	267	78	0	0	0	0	30	61	97	PM2.5
2000	346	282	63	1	0	0	0	28	58	111	PM2.5
1999	197	152	45	0	0	0	0	30	55	72	PM2.5
1998	179	176	3	0	0	0	0	19	32	67	PM10
1997	188	179	9	0	0	0	0	22	43	68	PM10
1996	173	153	20	0	0	0	0	22	51	96	PM10
1995	173	162	11	0	0	0	0	23	41	84	PM10
1994	179	154	23	2	0	0	0	28	54	122	PM10
1993	191	149	42	0	0	0	0	30	59	97	PM10
1992	173	150	23	0	0	0	0	31	52	83	PM10
1991	348	296	51	1	0	0	0	30	57	110	PM10
1990	362	314	47	1	0	0	0	31	53	113	PM10
1989	336	260	74	2	0	0	0	32	61	135	PM10
1988	334	242	87	5	0	0	0	34	66	124	PM10
1987	49	27	22	0	0	0	0	46	72	92	PM10
1986	54	31	23	0	0	0	0	46	66	92	PM10
1985	22	17	5	0	0	0	0	32	55	71	PM10
1984	10	5	5	0	0	0	0	53	61	61	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 1984–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem