Median AQI
34
Good
Louisiana · County air quality · 2025
St. James County, Louisiana
Median AQI 34 (Good). 92.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 34
- Median AQI
- 92.5%
- Good-air days
- 0
- Unhealthy days
- 81%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, St. James County's air is good on balance, cleaner than most US counties, a median AQI of 34 with 92.5% of 267 monitored days in the Good band, driven mainly by Ozone.
- 34
- median AQI · Good
- 92.5%
- days rated Good
- Ozone
- main pollutant
- 81%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Data updated July 2026
- Good · 247 d · 92.5%
- Moderate · 20 d · 7.5%
How did St. James County's air break down in 2025?
Across 267 monitored days, 247 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 84 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 267 days monitored. Median AQI: 34 (Good).
Insights: St. James County, Louisiana. EPA monitors recorded a median Air Quality Index of 34 across 267 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 247 (93%) fell in the Good band (AQI 0–50), 20 (7%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 84 (Moderate). Residents averaged about 27.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (267 days). Across the 2020–2025 trend window, good days shifted by -104 and the median AQI moved +5 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 84, moderate but never Unhealthy. Nearby counties show comparable readings: Ascension (94.1% good, AQI 33); Bossier (86.5% good, AQI 40); Caddo (84.3% good, AQI 38); Calcasieu (61.5% good, AQI 47); East Baton Rouge (49.3% good, AQI 51); Iberville (78.4% good, AQI 41).
Air Quality Summary
Good Days
92.5%
247 of 267 monitored days
17.5pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Excellent
90th-pct AQI 49
St. James County, Good days share 92.5%
National avg
Share of monitored days at AQI 0-50 (Good band).
St. James County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 267 monitored days across EPA AQI categories.
Good
247
93%
Moderate
20
7%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in St. James County.
- Ozone · 267 days · 100.0%
Health Impact Assessment
Excellent
St. James County's air quality is rated Excellent based on 92.5% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.5% of monitored days in 2025, with a median AQI of 34. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 267 of 267 monitored days.
5-Year Air Quality Trend
Air quality is worsening in St. James County. Best year: 2020 (351 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 351 | 6 | 0 | 0 | 29 | 90 |
| 2021 | 326 | 4 | 0 | 0 | 28 | 58 |
| 2022 | 345 | 16 | 0 | 0 | 32 | 93 |
| 2023 | 314 | 35 | 2 | 0 | 33 | 115 |
| 2024 | 339 | 21 | 3 | 0 | 32 | 108 |
| 2025 | 247 | 20 | 0 | 0 | 34 | 84 |
How does St. James County compare?
How St. James County compares
Good-day share better than US avg
St. James County 92.5%
Ascension County, Louisiana 94.1%
US average 76.5%
Median AQI better than US avg
St. James County 34
Ascension County, Louisiana 33
US average 38
Unhealthy days / yr about average
St. James County 0
Ascension County, Louisiana 0
US average 0
Other Counties in Louisiana
Air quality comparison for nearby counties in Louisiana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to St. James County.
Belknap County, New Hampshire
AQI 34 · 87.9% good
Dyer County, Tennessee
AQI 34 · 79.4% good
Flagler County, Florida
AQI 34 · 97.4% good
Grant County, Oregon
AQI 34 · 66.7% good
Highlands County, Florida
AQI 34 · 93.2% good
Johnson County, Texas
AQI 34 · 91.6% good
What St. James County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 34 means for exposure. Health guidance
- See how St. James County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare St. James County with its Louisiana neighbours before drawing a conclusion about the region. All of Louisiana
Based on 267 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in St. James County, Louisiana? ▼
St. James County has a median Air Quality Index (AQI) of 34, rated "Good." 92.5% of monitored days (247 out of 267) had good air quality in 2025.
What is the main pollutant in St. James County? ▼
The primary pollutant in St. James County is Ozone (O3), which was the main AQI driver on 267 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does St. James County have? ▼
In 2025, St. James County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 84.
Is the air quality in St. James County getting better or worse? ▼
Air quality in St. James County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 351 good days. Worst year: 2025 with 247 good days.
What does AQI 34 mean for health? ▼
St. James County's median AQI of 34 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does St. James County compare to other counties in Louisiana? ▼
St. James County has 92.5% good air days. Nearby counties in Louisiana: Ascension (94.1% good), Bossier (86.5% good), Caddo (84.3% good), Calcasieu (61.5% good), East Baton Rouge (49.3% good), Iberville (78.4% good).
What is the 90th percentile AQI in St. James County? ▼
The 90th percentile AQI for St. James County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 84 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.