Middlesex, Connecticut Air Quality
Middlesex County, Connecticut (CT)
→ Stableover 10 years
How Middlesex, Connecticut Air Quality Compares
Middlesex, Connecticut's median AQI of 43is 5% 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.
Middlesex, Connecticut Air Quality: The Full Picture
Middlesex, Connecticut (Middlesex County) holds an AirHistory Air Quality Grade of B (good, scoring 65 out of 100), built from 10 years of EPA Air Quality System monitoring. Its median AQI held flat between 2014 (43) and 2023 (43), and the five-year median now sits at 40 — 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 209 of 209 monitored days (100% of the year), making it the controlling pollutant for the B grade. The single worst reading logged that year hit an AQI of 140 (Unhealthy for Sensitive Groups), while the 90th-percentile day — the level the dirtiest 10% of days reach — came in at 64.
In 2023, Middlesex County recorded 170 "Good" air days (81% of the 209 days with valid AQI data), 35 "Moderate" days, and 4 days at "Unhealthy for Sensitive Groups" or above. Over the most recent five years on record, monitors logged 30 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 0.29 points per year on average. The cleanest year in the record was 2020 (median AQI 39), and the most polluted was 2016 (median AQI 44). Because the data come straight from federally certified EPA monitors, these figures track the Connecticut 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 | 43 | 64 | 140 | 170 | 35 | 4 | Ozone |
| 2022 | 40 | 67 | 147 | 173 | 33 | 6 | Ozone |
| 2021 | 39 | 80 | 151 | 171 | 25 | 11 | Ozone |
| 2020 | 39 | 54 | 129 | 182 | 24 | 2 | Ozone |
| 2019 | 41 | 61 | 154 | 175 | 23 | 7 | Ozone |
| 2018 | 40 | 67 | 126 | 168 | 32 | 8 | Ozone |
| 2017 | 40 | 61 | 151 | 171 | 28 | 8 | Ozone |
| 2016 | 44 | 97 | 187 | 125 | 36 | 13 | Ozone |
| 2015 | 43 | 90 | 147 | 134 | 37 | 12 | Ozone |
| 2014 | 43 | 80 | 151 | 140 | 31 | 11 | Ozone |
What This Means for Middlesex County Residents
Middlesex, Connecticut has received an Air Quality Grade of B (65/100) based on a decade of monitoring data from the EPA's air quality monitoring program. The current median AQI of 43 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.
Frequently Asked Questions
Middlesex, Connecticut has a current median AQI of 43, which falls in the "Good" range. The area has received an Air Quality Grade of B (65/100) based on 10 years of EPA monitoring data.
Air quality in Middlesex, Connecticut is stable over the past decade. The median AQI has changed by 0 points from 2014 to 2023.
Middlesex, Connecticut 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 Middlesex, Connecticut is Ground-Level Ozone. This is the dominant contributor to elevated AQI readings in the Middlesex County area.
Middlesex, Connecticut 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 43 (Good), outdoor exercise in Middlesex, Connecticut is generally safe year-round. Middlesex, Connecticut averages 6 days per year when athletes should move workouts indoors.