Bad Air Days in Baltimore County, Maryland: 8 a Year

8 bad air days a year

More bad air days than three quarters of monitored counties. Ranked 113 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (5% particle days).

When the bad days come in Baltimore

Most bad days here fall in July and June and August. Averaged over 2016 to 2025.

Is a purifier worth it here?

Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.

Better or worse than it was

In 2000 to 2009 this county averaged 28 bad days a year; in 2016 to 2025, 8. The air has improved. The worst recent year was 2016, with 22 bad days on 366 monitored days.

Date	AQI	Main pollutant
2023-06-29	205	Ozone
2016-07-27	204	Ozone
2023-06-08	180	PM2.5
2017-06-13	166	Ozone
2016-07-26	164	Ozone

The air on a normal day

Across 3,652 monitored days from 2016 to 2025, the air in Baltimore County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 34%. The median day sat at AQI 45; one day in ten went above 70.

The pollutant setting the AQI on an ordinary day here:

ozone56%2,057 days
fine particles (PM2.5)40%1,479 days
nitrogen dioxide3%116 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	236	126	3	0	45	129
2024	366	240	121	5	0	45	115
2023	365	228	124	13	4	45	205
2022	365	238	126	1	0	45	122
2021	365	207	148	10	0	47	140
2020	365	257	106	2	0	43	105
2019	365	232	124	9	0	46	150
2018	365	218	142	5	0	46	115
2017	365	262	91	12	1	43	166
2016	366	200	144	22	5	48	204
2015	365	242	110	13	0	43	143
2014	365	257	105	3	0	42	136
2013	365	256	105	4	0	41	119
2012	366	228	113	25	2	44	204
2011	363	227	110	26	6	43	190
2010	362	217	111	34	4	46	210

*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.