Bad Air Days in St. John the Baptist Parish, Louisiana: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 701 of 996 monitored counties, where 1 is worst.

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

The bad-air season here

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

Is a purifier worth it 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 worst days on file

In 2000 to 2009 this county averaged 13 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2023, with 4 bad days on 358 monitored days.

Date	AQI	Main pollutant
2023-08-18	112	Ozone
2018-06-08	108	Ozone
2021-06-14	108	Ozone
2023-08-17	108	Ozone
2016-04-05	105	Ozone

An ordinary day in St. John the Baptist

Across 3,569 monitored days from 2016 to 2025, the air in St. John the Baptist Parish rated Good on 93% of them, more often than the 72% typical of monitored counties, and Moderate on 6%. The median day sat at AQI 33; one day in ten went above 49.

The pollutant setting the AQI on an ordinary day here:

ozone100%3,569 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	364	339	25	0	0	34	87
2024	359	320	37	2	0	36	105
2023	358	315	39	4	0	35	112
2022	351	335	16	0	0	33	80
2021	336	327	8	1	0	31	108
2020	351	341	10	0	0	31	80
2019	364	334	30	0	0	33	93
2018	359	336	22	1	0	31	108
2017	362	337	25	0	0	33	100
2016	365	347	17	1	0	35	105
2015	365	341	22	2	0	33	105
2014	352	322	29	1	0	35	108
2013	364	332	30	2	0	36	105
2012	359	284	65	10	0	40	129
2011	363	291	61	11	1	37	151
2010	365	297	61	7	0	38	115

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

Elsewhere in Louisiana

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.