Saint Charles, Missouri Air Quality
Saint Charles County, Missouri (MO)
→ Stableover 10 years
How Saint Charles, Missouri Air Quality Compares
Saint Charles, Missouri's median AQI of 45is 10% worse than the national average of 41. The area averages 6 unhealthy air days per year. The primary pollutant of concern is Ground-Level Ozone.
Saint Charles, Missouri Air Quality: The Full Picture
Saint Charles, Missouri (Saint Charles County) holds an AirHistory Air Quality Grade of C (fair, scoring 63 out of 100), built from 10 years of EPA Air Quality System monitoring. Its median AQI rose 2 points between 2014 (43) and 2023 (45), and the five-year median now sits at 42 — inside the "Good" band on the EPA scale.
The pollutant driving most of the area's AQI readings is Ground-Level Ozone. In 2023, it set the daily AQI on 245 of 245 monitored days (100% of the year), making it the controlling pollutant for the C grade. The single worst reading logged that year hit an AQI of 147 (Unhealthy for Sensitive Groups), while the 90th-percentile day — the level the dirtiest 10% of days reach — came in at 87.
In 2023, Saint Charles County recorded 156 "Good" air days (64% of the 245 days with valid AQI data), 74 "Moderate" days, and 15 days at "Unhealthy for Sensitive Groups" or above. Over the most recent five years on record, monitors logged 32 days that crossed into "Unhealthy for Sensitive Groups" or worse — about 6 per year.
The decade-long trend is essentially flat, with year-to-year median AQI shifting by less than 0.07 points per year on average. The cleanest year in the record was 2020 (median AQI 39), and the most polluted was 2023 (median AQI 45). Because the data come straight from federally certified EPA monitors, these figures track the Missouri county the monitors physically sit in rather than a city boundary.
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10-Year AQI Trend
The solid line shows the median AQI each year. The dashed line shows the 90th percentile (worst 10% of days).
Air Quality Day Breakdown
Number of days per year in each EPA AQI category. Green = Good (AQI 0-50), Yellow = Moderate (51-100), Orange = Unhealthy for Sensitive Groups (101-150), Red = Unhealthy or worse (151+).
Year-by-Year Data
| Year | Median AQI | 90th Pct | Max AQI | Good Days | Moderate | Unhealthy+ | Pollutant |
|---|---|---|---|---|---|---|---|
| 2023 | 45 | 87 | 147 | 156 | 74 | 15 | Ozone |
| 2022 | 42 | 64 | 129 | 206 | 32 | 7 | Ozone |
| 2021 | 41 | 54 | 119 | 209 | 34 | 2 | Ozone |
| 2020 | 39 | 54 | 112 | 216 | 25 | 4 | Ozone |
| 2019 | 42 | 58 | 151 | 202 | 38 | 4 | Ozone |
| 2018 | 42 | 71 | 147 | 190 | 47 | 8 | Ozone |
| 2017 | 44 | 71 | 159 | 185 | 56 | 4 | Ozone |
| 2016 | 44 | 77 | 151 | 154 | 48 | 12 | Ozone |
| 2015 | 42 | 74 | 126 | 174 | 37 | 3 | Ozone |
| 2014 | 43 | 84 | 126 | 166 | 40 | 8 | Ozone |
What This Means for Saint Charles County Residents
Saint Charles, Missouri has received an Air Quality Grade of C (63/100) based on a decade of monitoring data from the EPA's air quality monitoring program. The current median AQI of 45 falls in the "Good" range.
The primary pollutant affecting this area is Ground-Level Ozone. Over the past 5 years, this area has averaged 6 unhealthy air quality days per year, days when sensitive groups (children, elderly, those with respiratory conditions) should limit outdoor activity. The American Lung Association's State of the Air report provides additional context on long-term health risks from air pollution exposure.
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Frequently Asked Questions
Saint Charles, Missouri has a current median AQI of 45, which falls in the "Good" range. The area has received an Air Quality Grade of C (63/100) based on 10 years of EPA monitoring data.
Air quality in Saint Charles, Missouri is stable over the past decade. The median AQI has changed by +2 points from 2014 to 2023.
Saint Charles, Missouri averages 6 unhealthy air quality days per year over the past 5 years. On these days, sensitive groups including children, the elderly, and those with respiratory conditions should limit outdoor activity.
The primary pollutant affecting Saint Charles, Missouri is Ground-Level Ozone. This is the dominant contributor to elevated AQI readings in the Saint Charles County area.
Saint Charles, Missouri averages 6 unhealthy air days per year. Asthma patients should monitor daily AQI readings and limit outdoor activity when AQI exceeds 100. The primary pollutant is Ground-Level Ozone, which is a known asthma trigger.
With a median AQI of 45 (Good), outdoor exercise in Saint Charles, Missouri is generally safe year-round. Saint Charles, Missouri averages 6 days per year when athletes should move workouts indoors.