Bad Air Days in Butler County, Ohio: 6 a Year

6 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 174 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (33% particle days).

Which months to watch

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

Is a purifier worth it here?

Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.

Better or worse than it was

In 2000 to 2009 this county averaged 33 bad days a year; in 2016 to 2025, 6. The air has improved. The worst recent year was 2023, with 16 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	197	PM2.5
2023-06-27	164	PM2.5
2023-06-07	153	PM2.5
2023-06-29	152	PM2.5
2025-07-23	151	Ozone

Most days, not the worst ones

Across 3,647 monitored days from 2016 to 2025, the air in Butler County rated Good on 52% of them, less often than the 72% typical of monitored counties, and Moderate on 46%. The median day sat at AQI 49; one day in ten went above 72.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)51%1,842 days
ozone48%1,766 days
coarse dust (PM10)1%39 days

Butler County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	121	239	5	1	55	151
2024	366	154	209	3	0	53	122
2023	365	107	242	16	4	56	197
2022	365	146	215	4	0	53	119
2021	365	128	232	5	0	55	116
2020	366	279	84	3	0	41	126
2019	364	236	126	2	0	44	101
2018	365	241	118	6	0	42	140
2017	364	248	110	6	0	43	126
2016	362	234	117	11	0	44	136
2015	360	237	120	3	0	44	112
2014	359	231	123	5	0	44	133
2013	365	232	130	3	0	44	119
2012	361	183	146	32	4	50	179
2011	349	196	129	24	1	47	172
2010	362	193	141	28	1	49	151

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

Elsewhere in Ohio

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.