Louisiana · County air quality · 2025
St. Martin County, Louisiana
Median AQI 36 (Good). 92.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 36
- Median AQI
- 92.2%
- Good-air days
- 0
- Unhealthy days
- 85%
- Cleaner than US counties
St. Martin County's 2025 annual median AQI is 36 (Good), with 92.2% Good days
According to the U.S. EPA Air Quality System, St. Martin County, Louisiana posted a 2025 median AQI of 36 (Good) across 360 monitored days, with 92.2% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- St. Martin County's 92.2% Good-day share places it cleaner than 85% of US counties in 2025.
- Closest median-AQI peer
- Ashland County (81.6% Good, median AQI 36) is the closest nationwide median-AQI peer to St. Martin County.
- 2020–2025 trend
- St. Martin County's floor-qualifying Good-day share is stable from 2020 to 2025 (94.1% → 92.2%).
- Median AQI
- Median AQI: 36
According to the 2025 EPA AQS county release on PlainAirData, St. Martin County, Louisiana ranks #233 of 951 by median AQI (36) and #141 by good-day share (92.2%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Annual release change
What changed in the 2025 EPA annual release
- St. Martin County's Good-day share rose from 88.0% to 92.2% between the 2024 and 2025 EPA annual releases, a change of +4.3 percentage points.
- St. Martin County's peak single-day AQI fell from 101 to 77 between the 2024 and 2025 EPA annual releases, a change of -24 points.
Data updated August 2026
- Good · 332 d · 92.2%
- Moderate · 28 d · 7.8%
How did St. Martin County's air break down in 2025?
Across 360 monitored days, 332 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 77 (Moderate).
EPA AQS →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where St. Martin County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. St. Martin County's Good-day share is 92.2% - cleaner than 85% of that comparison set.
St. Martin County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
92.2% Cleaner than 85% higher than 85% of 951 US counties
Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in St. Martin County.
- Ozone · 360 days · 100.0%
2024 daily-monitor rhythm in St. Martin County
Month-by-month median AQI from EPA day-level county monitors (332 reported days in 2024). Oct posted the highest typical readings (median AQI 48, peak 97); Jul was cleanest at median 27.
Five-year seasonal record
EPA day-level county files · 2020–20241,752 daily readings show a recurring local pattern: Apr has the highest matched-month median AQI (44), while Jul is lowest (27). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
St. Martin County's air quality is rated Excellent based on 92.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 92.2% of monitored days in 2025, with a median AQI of 36. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 360 of 360 monitored days.
5-Year Air Quality Trend
Air quality is stable in St. Martin County. Highest Good-day share: 2021 (96.4%, 347 of 360 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 337 | 21 | 0 | 0 | 33 | 87 |
| 2021 | 347 | 13 | 0 | 0 | 34 | 87 |
| 2022 | 296 | 42 | 0 | 0 | 34 | 97 |
| 2023 | 316 | 47 | 1 | 0 | 37 | 112 |
| 2024 | 292 | 39 | 1 | 0 | 38 | 101 |
| 2025 | 332 | 28 | 0 | 0 | 36 | 77 |
How does St. Martin County compare?
How St. Martin County compares
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for St. Martin County, Louisiana · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
Every figure on PlainAirData 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.