Bad Air Days in Bartholomew County, Indiana: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 519 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (21% particle days).

Which months to watch

Most bad days here fall in June and May. 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.

The record for Bartholomew

The worst recent year was 2023, with 8 bad days on 361 monitored days.

Date	AQI	Main pollutant
2023-06-28	215	PM2.5
2023-06-27	145	PM2.5
2023-06-06	122	Ozone
2023-06-29	121	PM2.5
2023-05-24	119	Ozone

Most days, not the worst ones

Across 3,646 monitored days from 2016 to 2025, the air in Bartholomew County rated Good on 69% of them, close to the 72% typical of monitored counties, and Moderate on 30%. The median day sat at AQI 44; one day in ten went above 60.

The pollutant setting the AQI on an ordinary day here:

ozone50%1,831 days
fine particles (PM2.5)50%1,809 days

Bartholomew County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	265	100	0	0	43	97
2024	366	262	103	1	0	44	101
2023	361	234	119	8	1	46	215
2022	365	280	84	1	0	41	105
2021	364	252	112	0	0	43	93
2020	366	275	91	0	0	41	97
2019	364	256	108	0	0	44	77
2018	365	242	119	4	0	44	108
2017	364	256	108	0	0	43	93
2016	366	211	150	5	0	47	105
2015	365	178	185	2	0	51	115
2014	364	234	129	1	0	43	108
2013	214	175	39	0	0	35	93

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

Indiana 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.