Bad Air Days in Hamilton County, Tennessee: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 543 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (35% particle days).

When the bad days come in Hamilton

Most bad days here fall in June and July. 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 2016, with 3 bad days on 288 monitored days.

Date	AQI	Main pollutant
2016-11-14	186	PM2.5
2020-07-05	151	PM2.5
2025-03-27	141	PM2.5
2023-07-17	137	PM2.5
2025-03-28	137	PM2.5

The air on a normal day

Across 3,491 monitored days from 2016 to 2025, the air in Hamilton County rated Good on 54% of them, less often than the 72% typical of monitored counties, and Moderate on 45%. The median day sat at AQI 49; one day in ten went above 65.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)65%2,277 days
ozone35%1,214 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	237	126	2	0	44	141
2024	349	190	156	3	0	48	126
2023	365	175	187	3	0	51	137
2022	341	169	171	1	0	51	105
2021	351	191	159	1	0	48	101
2020	364	219	144	1	1	46	151
2019	365	181	184	0	0	51	97
2018	365	193	171	1	0	48	101
2017	338	156	180	2	0	51	108
2016	288	179	106	3	1	47	186
2015	284	211	70	3	0	43	133
2014	287	193	93	1	0	44	105
2013	288	200	87	1	0	45	101
2012	285	148	127	10	2	50	161
2011	300	145	145	10	0	51	129
2010	301	136	145	20	1	52	159

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

Elsewhere in Tennessee

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.