Bad Air Days in DeKalb County, Georgia: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 353 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (19% particle days).

Which months to watch

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 37 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2016, with 9 bad days on 366 monitored days.

Date	AQI	Main pollutant
2019-09-09	159	Ozone
2016-11-14	151	PM2.5
2022-06-20	147	Ozone
2016-06-30	143	Ozone
2017-05-15	143	Ozone

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in DeKalb County rated Good on 48% of them, less often than the 72% typical of monitored counties, and Moderate on 51%. The median day sat at AQI 51; one day in ten went above 66.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)75%2,727 days
ozone20%737 days
nitrogen dioxide5%188 days

DeKalb County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	213	152	0	0	47	90
2024	366	178	182	6	0	51	133
2023	365	140	218	7	0	53	136
2022	365	177	186	2	0	51	147
2021	365	190	173	2	0	49	119
2020	366	215	150	1	0	46	106
2019	365	173	188	4	1	52	159
2018	365	195	170	0	0	49	100
2017	365	174	190	1	0	51	143
2016	366	107	250	9	1	57	151
2015	365	111	250	4	0	56	150
2014	365	86	276	3	0	56	122
2013	365	114	250	1	0	55	140
2012	366	87	266	13	3	61	185
2011	365	84	263	18	2	58	172
2010	365	66	288	11	2	61	182

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

Elsewhere in Georgia

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.