Bad Air Days in Madison County, Ohio: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 559 of 996 monitored counties, where 1 is worst.

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

The bad-air season here

Most bad days here fall in June and September. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 35 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2025, with 5 bad days on 244 monitored days.

Date	AQI	Main pollutant
2016-09-23	112	Ozone
2025-09-19	112	Ozone
2025-06-12	108	Ozone
2025-09-14	108	Ozone
2016-06-11	105	Ozone

The air on a normal day

Across 2,396 monitored days from 2016 to 2025, the air in Madison County rated Good on 85% of them, more often than the 72% typical of monitored counties, and Moderate on 15%. The median day sat at AQI 41; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,396 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	244	193	46	5	0	43	112
2024	245	203	42	0	0	44	100
2023	243	197	44	2	0	44	105
2022	244	218	26	0	0	39	90
2021	229	212	17	0	0	39	84
2020	245	220	25	0	0	39	84
2019	245	209	36	0	0	42	93
2018	244	209	34	1	0	41	101
2017	244	211	32	1	0	41	105
2016	213	161	50	2	0	43	112
2015	214	172	41	1	0	42	108
2014	205	169	33	3	0	43	108
2013	213	177	36	0	0	42	97
2012	214	126	78	10	1	47	174
2011	213	146	53	14	0	44	143
2010	210	132	70	8	0	47	126

*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.