Bad Air Days in Carroll County, Maryland: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 532 of 996 monitored counties, where 1 is worst.

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

When the bad days come in Carroll

Most bad days here fall in June and May. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 36 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2016, with 4 bad days on 212 monitored days.

Date	AQI	Main pollutant
2023-06-29	143	Ozone
2016-06-01	122	Ozone
2016-05-26	115	Ozone
2016-09-23	115	Ozone
2021-05-20	112	Ozone

The air on a normal day

Across 2,392 monitored days from 2016 to 2025, the air in Carroll County rated Good on 84% of them, more often than the 72% typical of monitored counties, and Moderate on 16%. The median day sat at AQI 41; one day in ten went above 59.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,392 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	238	215	23	0	0	38	90
2024	244	189	55	0	0	42	93
2023	244	183	57	4	0	44	143
2022	243	210	32	1	0	42	112
2021	243	208	34	1	0	41	112
2020	242	225	17	0	0	39	84
2019	241	205	35	1	0	43	101
2018	240	199	41	0	0	41	97
2017	245	201	43	1	0	41	108
2016	212	167	41	4	0	42	122
2015	213	162	49	2	0	43	115
2014	214	163	51	0	0	43	84
2013	209	162	46	1	0	43	101
2012	213	141	61	11	1	45	159
2011	211	148	54	9	0	44	150
2010	212	128	63	21	0	46	150

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

Elsewhere in Maryland

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.