Bad Air Days in McLennan County, Texas: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 535 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (18% particle days).

When the bad days come in McLennan

Most bad days here fall in August and September 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 worst days on file

In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 8 bad days on 365 monitored days.

Date	AQI	Main pollutant
2025-03-15	142	PM2.5
2024-07-10	133	Ozone
2023-08-30	129	Ozone
2023-09-02	122	Ozone
2023-09-12	122	Ozone

Most days, not the worst ones

Across 3,425 monitored days from 2016 to 2025, the air in McLennan County rated Good on 67% of them, less often than the 72% typical of monitored counties, and Moderate on 32%. The median day sat at AQI 44; one day in ten went above 61.

The pollutant setting the AQI on an ordinary day here:

ozone53%1,826 days
fine particles (PM2.5)46%1,572 days
carbon monoxide1%22 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	170	192	3	0	51	142
2024	365	126	234	5	0	53	133
2023	365	169	188	8	0	52	129
2022	364	209	155	0	0	48	100
2021	364	280	84	0	0	39	100
2020	366	294	72	0	0	39	97
2019	365	313	52	0	0	39	87
2018	312	248	64	0	0	38	98
2017	193	166	26	1	0	39	112
2016	366	327	39	0	0	37	76
2015	365	250	112	3	0	42	115
2014	365	236	128	1	0	44	105
2013	361	233	124	4	0	45	115
2012	366	257	105	4	1	43	154
2011	365	195	151	19	0	49	147
2010	365	252	111	2	0	44	115

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

Texas 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.