Bad Air Days in Fairfax County, Virginia: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 401 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (36% particle days).

Which months to watch

Most bad days here fall in June and July and August. 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 Fairfax

In 2000 to 2009 this county averaged 33 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2023, with 10 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-08	222	PM2.5
2023-06-07	184	PM2.5
2023-06-29	177	PM2.5
2023-06-02	147	Ozone
2023-06-28	131	PM2.5

Most days, not the worst ones

Across 3,653 monitored days from 2016 to 2025, the air in Fairfax County rated Good on 62% of them, less often than the 72% typical of monitored counties, and Moderate on 37%. The median day sat at AQI 46; one day in ten went above 62.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)61%2,237 days
ozone34%1,249 days
nitrogen dioxide5%167 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	284	80	1	0	42	124
2024	366	263	100	3	0	42	112
2023	365	217	138	10	3	46	222
2022	365	232	133	0	0	47	87
2021	365	208	153	4	0	47	129
2020	366	236	130	0	0	44	100
2019	365	192	171	2	0	49	105
2018	365	203	161	1	0	48	101
2017	365	206	158	1	0	49	105
2016	366	228	132	6	0	44	129
2015	365	217	144	4	0	46	119
2014	363	219	143	1	0	46	105
2013	365	220	144	1	0	46	119
2012	364	190	153	21	3	49	201
2011	360	179	165	16	4	51	185
2010	365	172	170	23	6	52	174

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

Virginia 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.