Bay St. Louis, Mississippi Air Quality
Bay St. Louis has a median AQI of 44, earning an air quality grade of A- — excellent air quality that ranks better than 31% of US cities. Air quality has been trending worse over the past decade, a concern for local residents and health officials. Particulate matter (PM2.5) is the primary concern, often linked to vehicle traffic, industrial activity, and wildfire smoke. In 2025, Bay St. Louis recorded 185 good air quality days (68% of monitored days).
Population: 10,188 • County: Hancock
Current AQI
Quick Facts
| Current AQI | 23 — Good |
| Air Quality Grade | A- |
| Median AQI (2025) | 44 |
| vs. U.S. Cities | Better than 31% |
| Primary Pollutant | PM2.5 |
| Unhealthy Days/Year | 0 |
| 10-Year Trend | ↓ Worsening |
| Data Source | EPA AQS (historical) · AirNow (live) |
Health Recommendation
Air quality is satisfactory, and air pollution poses little or no risk.
It's a great day to be active outside!
5-Day AQI Forecast
Last 90 Days
Current Pollutant Levels
Real-time data from EPA AirNow
Local Air Quality Context
Air quality data for Bay St. Louis is sourced from the WAVELAND monitoring area, located approximately 2 miles from city center. This EPA-certified station continuously tracks particulate matter (PM2.5), the primary driver of air quality alerts in this area.
Bay St. Louis tends to see elevated PM2.5 readings during fall and winter months when temperature inversions trap pollutants near the surface. Wood burning, vehicle exhaust, and reduced wind speeds compound the effect. Residents with respiratory conditions should monitor forecasts closely between November and February.
AQI Trend (10 Years)
Air Quality Days by Year
Bay St. Louis Median AQI by Year
Annual EPA air quality data for Bay St. Louis — median AQI, day-category breakdown, and primary pollutant per year.
| Year | Median AQI | Good Days | Unhealthy Days | Max AQI | Primary Pollutant |
|---|---|---|---|---|---|
| 2025 | 44 | 185 | — | 84 | PM2.5 |
| 2024 | 43 | 245 | — | 87 | PM2.5 |
| 2023 | 50 | 188 | 1 | 112 | PM2.5 |
| 2022 | 44 | 238 | — | 89 | PM2.5 |
| 2021 | 45 | 225 | — | 97 | PM2.5 |
| 2020 | 45 | 217 | — | 90 | PM2.5 |
| 2019 | 43 | 263 | — | 80 | PM2.5 |
| 2018 | 41 | 257 | 1 | 102 | PM2.5 |
| 2017 | 40 | 225 | — | 77 | Ozone |
| 2016 | 40 | 234 | — | 90 | Ozone |
Source: EPA Air Quality System (AQS) annual summaries. "Unhealthy Days" includes Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous categories.
2025 Air Quality Summary
Primary Pollutant Days (2025)
Days when each pollutant was the primary driver of AQI. Learn about pollutants →
Frequently Asked Questions About Bay St. Louis Air Quality
What is the air quality in Bay St. Louis today?
The current AQI in Bay St. Louis is 23, rated "Good". Air quality is good — outdoor activity is safe for everyone today. Air quality is satisfactory, and air pollution poses little or no risk.
Is air quality in Bay St. Louis getting better or worse?
Air quality in Bay St. Louis has been worsening. The median AQI has risen 4 points (from 40 in 2016 to 44 in 2025), a concern for local health officials.
What is the most common air pollutant in Bay St. Louis?
PM2.5 is the primary air pollutant in Bay St. Louis, responsible for 170 days (62% of monitored days) in 2025. Particulate matter originates from vehicle exhaust, wildfires, construction, and industrial activity.
How many unhealthy air days does Bay St. Louis have per year?
In 2025, Bay St. Louis recorded 68% good air quality days (185 days) out of 273 monitored days. There were 0 Unhealthy for Sensitive Groups days and 0 Unhealthy days (AQI above 100). The highest single-day AQI recorded was 84.
What air quality grade does Bay St. Louis receive?
Bay St. Louis receives an air quality grade of A-, placing it better than 31% of US cities. This is based on a median AQI of 44 in 2025, with 185 good air quality days. The EPA monitors air quality in this area continuously using certified monitoring stations.
Air Quality Grade
Better than 31% of US cities
Nearby Cities
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National Rankings
See how Bay St. Louis compares to every other US city by air quality.
Best Air Quality Cities →All city rankingsRecommended Air Purifiers for Bay St. Louis
Bay St. Louis sees its worst PM2.5 during winter temperature inversions when particulates get trapped near ground level. A unit with True HEPA and an auto-mode sensor is most effective for responding to these spikes.
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