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

4 bad air days a year

About the middle of monitored US counties. Ranked 268 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (71% particle days).

When the bad days come in Marion

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

What actually helps here

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The record for Marion

In 2000 to 2009 this county averaged 4 bad days a year; in 2016 to 2025, 4. Not much has changed. The worst recent year was 2020, with 11 bad days on 365 monitored days.

Date	AQI	Main pollutant
2020-09-11	1272	PM2.5
2020-09-09	998	PM2.5
2020-09-13	992	PM2.5
2020-09-12	927	PM2.5
2020-09-10	798	PM2.5

Most days, not the worst ones

Across 3,629 monitored days from 2016 to 2025, the air in Marion County rated Good on 77% of them, more often than the 72% typical of monitored counties, and Moderate on 22%. The median day sat at AQI 35; one day in ten went above 61.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)65%2,363 days
ozone35%1,266 days

Marion County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	292	73	0	0	35	85
2024	366	298	64	4	0	35	129
2023	365	268	93	4	0	38	128
2022	365	254	104	7	2	36	168
2021	363	280	83	0	0	36	93
2020	365	278	76	11	10	36	1272
2019	356	262	94	0	0	37	93
2018	361	271	84	6	0	35	125
2017	362	287	66	9	0	33	150
2016	361	304	57	0	0	33	97
2015	365	267	95	3	2	37	176
2014	365	287	77	1	1	34	155
2013	361	247	109	5	0	37	123
2012	364	285	79	0	0	33	93
2011	365	277	88	0	0	34	96
2010	365	291	73	1	0	31	126

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

Nearby counties on file

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.