Bad Air Days in Calvert County, Maryland: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 626 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 May 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.

Better or worse than it was

In 2000 to 2009 this county averaged 30 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2016, with 3 bad days on 214 monitored days.

Date	AQI	Main pollutant
2018-07-10	147	Ozone
2016-05-26	115	Ozone
2016-04-19	112	Ozone
2016-07-27	108	Ozone
2017-05-17	108	Ozone

An ordinary day in Calvert

Across 2,344 monitored days from 2016 to 2025, the air in Calvert County rated Good on 89% of them, more often than the 72% typical of monitored counties, and Moderate on 11%. The median day sat at AQI 40; one day in ten went above 53.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,344 days

Calvert County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	240	227	13	0	0	38	77
2024	237	203	33	1	0	41	108
2023	238	206	31	1	0	42	101
2022	239	225	14	0	0	39	74
2021	223	205	17	1	0	39	105
2020	238	235	3	0	0	35	67
2019	232	214	18	0	0	39	71
2018	243	209	33	1	0	39	147
2017	240	199	40	1	0	43	108
2016	214	165	46	3	0	42	115
2015	206	145	61	0	0	44	93
2014	213	156	54	3	0	44	105
2013	211	175	33	3	0	42	105
2012	211	142	54	15	2	45	206
2011	209	148	47	14	3	44	169
2010	210	120	78	12	4	47	182

*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.