Bad Air Days in Clark County, Ohio: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 383 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (24% particle days).

The bad-air season here

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

What to buy, and what not to

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 worst days on file

In 2000 to 2009 this county averaged 30 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2023, with 8 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	196	PM2.5
2023-06-27	166	PM2.5
2023-06-29	155	PM2.5
2023-07-17	142	PM2.5
2018-07-14	140	Ozone

An ordinary day in Clark

Across 3,589 monitored days from 2016 to 2025, the air in Clark County rated Good on 55% of them, less often than the 72% typical of monitored counties, and Moderate on 44%. The median day sat at AQI 48; one day in ten went above 66.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)67%2,415 days
ozone33%1,174 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	363	223	138	2	0	45	126
2024	363	239	121	3	0	45	133
2023	365	187	170	8	3	50	196
2022	338	212	125	1	0	46	129
2021	365	169	196	0	0	52	100
2020	343	218	124	1	0	44	108
2019	362	147	213	2	0	53	105
2018	362	170	188	4	0	52	140
2017	365	209	154	2	0	47	105
2016	363	200	157	6	0	48	119
2015	365	183	175	7	0	50	133
2014	365	175	189	1	0	51	105
2013	365	157	202	6	0	52	112
2012	363	110	231	22	1	56	172
2011	365	140	210	15	0	54	140
2010	350	123	217	10	0	57	136

*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.