Bad Air Days in Cass County, Missouri: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 635 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (33% particle days).

Which months to watch

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

What to buy, and what not to

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 Cass

In 2000 to 2009 this county averaged 14 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 5 bad days on 332 monitored days.

Date	AQI	Main pollutant
2023-06-06	143	Ozone
2025-08-01	123	PM2.5
2023-06-04	119	Ozone
2017-05-26	115	Ozone
2023-06-07	115	Ozone

An ordinary day in Cass

Across 3,599 monitored days from 2016 to 2025, the air in Cass County rated Good on 77% of them, more often than the 72% typical of monitored counties, and Moderate on 23%. The median day sat at AQI 41; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)52%1,856 days
ozone48%1,743 days

Cass County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	362	281	80	1	0	41	123
2024	366	280	85	1	0	42	107
2023	332	242	85	5	0	44	143
2022	360	287	73	0	0	40	88
2021	365	267	97	1	0	42	108
2020	362	300	60	2	0	39	105
2019	365	289	76	0	0	42	93
2018	364	266	98	0	0	41	97
2017	359	253	104	2	0	43	115
2016	364	294	70	0	0	39	80
2015	336	206	129	1	0	45	103
2014	341	147	193	1	0	53	102
2013	361	201	160	0	0	48	97
2012	364	100	244	20	1	57	161
2011	363	173	184	6	0	52	122
2010	365	161	204	0	0	53	100

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

Missouri 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.