Bad Air Days in Umatilla County, Oregon: 5 a Year

5 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 225 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (83% particle days).

Which months to watch

Most bad days here fall in August and September. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 4 bad days a year; in 2016 to 2025, 5. Not much has changed. The worst recent year was 2017, with 12 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-12	738	PM2.5
2020-09-13	638	PM2.5
2020-09-11	469	PM2.5
2020-09-14	460	PM2.5
2020-09-15	316	PM2.5

Most days, not the worst ones

Across 3,621 monitored days from 2016 to 2025, the air in Umatilla County rated Good on 72% of them, close to the 72% typical of monitored counties, and Moderate on 26%. The median day sat at AQI 39; one day in ten went above 63.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)67%2,440 days
ozone33%1,181 days

Umatilla County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	260	105	0	0	41	95
2024	366	272	90	4	0	38	117
2023	365	259	103	3	3	42	267
2022	365	244	118	3	0	39	141
2021	365	265	92	8	2	38	169
2020	366	273	85	8	8	38	738
2019	365	267	97	1	0	40	104
2018	333	257	68	8	3	36	254
2017	365	222	131	12	3	44	252
2016	366	297	68	1	0	35	112
2015	365	246	110	9	3	41	160
2014	361	273	88	0	0	37	99
2013	364	220	138	6	0	45	115
2012	365	244	119	2	0	42	108
2011	362	274	87	1	0	39	104
2010	365	245	120	0	0	40	93

*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.