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

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 552 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (53% particle days).

Which months to watch

Most bad days here fall in June. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 13 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 9 bad days on 358 monitored days.

Date	AQI	Main pollutant
2023-06-28	204	PM2.5
2023-06-27	180	PM2.5
2023-06-29	153	PM2.5
2023-06-07	148	PM2.5
2022-06-21	136	Ozone

Most days, not the worst ones

Across 3,645 monitored days from 2016 to 2025, the air in Preble County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 37%. The median day sat at AQI 45; one day in ten went above 63.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)56%2,056 days
ozone43%1,582 days

Preble County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	247	116	2	0	43	115
2024	366	252	114	0	0	44	100
2023	358	213	136	9	3	46	204
2022	365	235	128	2	0	44	136
2021	365	205	160	0	0	47	97
2020	366	262	103	1	0	42	101
2019	364	201	163	0	0	48	93
2018	365	186	178	1	0	50	107
2017	365	230	134	1	0	44	108
2016	366	250	115	1	0	43	105
2015	365	233	131	1	0	44	105
2014	365	186	176	3	0	50	119
2013	361	157	203	1	0	52	113
2012	366	144	209	13	1	54	159
2011	365	144	216	5	0	53	136
2010	359	127	227	5	0	56	136

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

Ohio compared

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.