Bad Air Days in Union County, Oregon: 4 a Year

4 bad air days a year

About the middle of monitored US counties. Ranked 286 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (100% particle days).

Which months to watch

Most bad days here fall in September and August. Averaged over 2016 to 2025.

What actually helps here

Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.

The record for Union

In 2000 to 2009 this county averaged 2 bad days a year; in 2016 to 2025, 4. Not much has changed. The worst recent year was 2017, with 11 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-12	326	PM2.5
2020-09-13	284	PM2.5
2020-09-14	234	PM2.5
2017-09-07	218	PM2.5
2020-09-15	213	PM2.5

Most days, not the worst ones

Across 3,623 monitored days from 2016 to 2025, the air in Union County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 17%. The median day sat at AQI 27; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)100%3,611 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	353	298	55	0	0	27	79
2024	366	303	61	2	0	23	128
2023	361	305	56	0	0	26	95
2022	361	283	74	4	0	28	130
2021	360	304	49	7	2	27	170
2020	366	300	57	9	8	27	326
2019	365	313	52	0	0	26	88
2018	362	282	74	6	1	32	192
2017	365	277	77	11	3	31	218
2016	364	297	67	0	0	24	99
2015	362	254	97	11	5	38	191
2014	363	255	102	6	0	34	140
2013	365	221	139	5	0	44	145
2012	365	260	103	2	0	34	147
2011	363	267	91	5	1	29	153
2010	365	261	103	1	0	33	106

*2025 may be a partial year in EPA's file.

Oregon compared

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.