Bad Air Days in Jefferson County, Tennessee: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 697 of 996 monitored counties, where 1 is worst.

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

Which months to watch

Most bad days here fall in April and June and July and August. 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 37 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2016, with 2 bad days on 239 monitored days.

Date	AQI	Main pollutant
2016-06-11	133	Ozone
2016-04-20	112	Ozone
2023-06-10	112	Ozone
2023-04-20	108	Ozone
2024-08-28	105	Ozone

Most days, not the worst ones

Across 2,349 monitored days from 2016 to 2025, the air in Jefferson 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 42; one day in ten went above 56.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,349 days

Jefferson County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	237	215	22	0	0	41	93
2024	244	222	21	1	0	40	105
2023	241	210	29	2	0	42	112
2022	244	219	25	0	0	41	87
2021	235	199	36	0	0	41	100
2020	240	232	8	0	0	37	74
2019	234	197	37	0	0	44	93
2018	244	202	42	0	0	42	100
2017	191	148	42	1	0	43	101
2016	239	158	79	2	0	47	133
2015	245	183	61	1	0	44	101
2014	245	190	55	0	0	44	93
2013	242	197	43	2	0	43	101
2012	245	152	84	9	3	46	206
2011	245	162	75	8	0	46	147
2010	241	153	73	15	0	46	140

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

Nearby counties on file

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.