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

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 527 of 996 monitored counties, where 1 is worst.

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

Which months to watch

Most bad days here fall in July and April 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 Charles

In 2000 to 2009 this county averaged 37 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2016, with 6 bad days on 213 monitored days.

Date	AQI	Main pollutant
2016-07-27	133	Ozone
2018-07-10	133	Ozone
2024-08-28	119	Ozone
2016-04-19	115	Ozone
2023-04-13	115	Ozone

Most days, not the worst ones

Across 2,344 monitored days from 2016 to 2025, the air in Charles County rated Good on 88% of them, more often than the 72% typical of monitored counties, and Moderate on 12%. The median day sat at AQI 40; one day in ten went above 55.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,344 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	236	218	18	0	0	38	97
2024	232	209	21	2	0	40	119
2023	243	199	42	2	0	42	115
2022	245	225	20	0	0	41	87
2021	242	215	26	1	0	38	105
2020	236	235	1	0	0	34	58
2019	221	202	19	0	0	40	77
2018	235	202	32	1	0	39	133
2017	241	189	52	0	0	44	100
2016	213	166	41	6	0	42	133
2015	212	153	58	1	0	44	122
2014	209	173	33	3	0	44	122
2013	198	167	31	0	0	40	97
2012	196	142	41	13	3	45	192
2011	207	142	54	11	3	45	182
2010	213	128	72	13	3	47	169

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

Maryland 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.