Bad Air Days in Franklin County, Ohio: 4 a Year

4 bad air days a year

About the middle of monitored US counties. Ranked 290 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (44% particle days).

Which months to watch

Most bad days here fall in June and July. 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.

The record for Franklin

In 2000 to 2009 this county averaged 32 bad days a year; in 2016 to 2025, 4. The air has improved. The worst recent year was 2023, with 11 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	210	PM2.5
2023-06-29	183	PM2.5
2023-06-27	161	PM2.5
2025-06-12	156	Ozone
2023-07-17	153	PM2.5

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Franklin County rated Good on 51% of them, less often than the 72% typical of monitored counties, and Moderate on 48%. The median day sat at AQI 50; one day in ten went above 68.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)66%2,415 days
ozone31%1,143 days
nitrogen dioxide1%49 days
coarse dust (PM10)1%46 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	147	213	5	1	53	156
2024	366	151	211	4	0	53	118
2023	365	136	218	11	4	54	210
2022	365	206	157	2	0	48	143
2021	365	170	195	0	0	52	100
2020	366	232	132	2	0	45	102
2019	365	157	207	1	0	53	101
2018	365	210	153	2	0	47	122
2017	365	227	135	3	0	46	112
2016	366	220	137	9	0	46	126
2015	365	166	194	5	0	52	112
2014	365	129	230	6	0	54	115
2013	365	155	204	6	0	52	136
2012	366	117	225	24	3	55	201
2011	365	114	237	14	4	55	156
2010	365	129	217	19	1	56	156

*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.