Bad Air Days in Mason County, Michigan: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 414 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (0% particle days).

When the bad days come in Mason

Most bad days here fall in June. Averaged over 2016 to 2025.

Is a purifier worth it 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 Mason

The worst recent year was 2016, with 6 bad days on 180 monitored days.

Date	AQI	Main pollutant
2022-06-20	161	Ozone
2020-06-19	159	Ozone
2023-06-29	143	Ozone
2018-05-25	133	Ozone
2016-05-24	129	Ozone

Most days, not the worst ones

Across 2,339 monitored days from 2016 to 2025, the air in Mason County rated Good on 89% of them, more often than the 72% typical of monitored counties, and Moderate on 10%. The median day sat at AQI 37; one day in ten went above 53.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,339 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	213	190	23	0	0	36	87
2024	244	218	26	0	0	37	97
2023	221	178	41	2	0	40	143
2022	236	219	15	2	1	36	161
2021	243	206	34	3	0	38	115
2020	251	229	20	2	1	37	159
2019	254	244	10	0	0	35	64
2018	252	226	25	1	0	37	133
2017	245	217	27	1	0	38	108
2016	180	157	17	6	0	38	129
2015	183	159	23	1	0	39	105
2014	183	156	25	2	0	39	115
2013	181	141	38	2	0	40	112
2012	182	131	29	22	3	42	156
2011	183	159	20	4	1	38	172
2010	183	154	27	2	0	39	126

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

Elsewhere in Michigan

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, and on why a purifier does not touch ozone in smoke vs ozone.