Bad Air Days in Middlesex County, Connecticut: 13 a Year
13 bad air days a year
Among the worst tenth of monitored US counties. Ranked 60 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in July and June and August and May. Averaged over 2016 to 2025.
What to buy, and what not to
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
- Sign up for EnviroFlash ozone alerts for this area during the worst months.
Better or worse than it was
In 2000 to 2009 this county averaged 34 bad days a year; in 2016 to 2025, 13. The air has improved. The worst recent year was 2016, with 13 bad days on 174 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2016-07-22 | 187 | Ozone |
| 2024-06-20 | 177 | Ozone |
| 2016-05-26 | 164 | Ozone |
| 2019-07-16 | 154 | Ozone |
| 2017-05-18 | 151 | Ozone |
The air on a normal day
Across 2,052 monitored days from 2016 to 2025, the air in Middlesex County rated Good on 82% of them, more often than the 72% typical of monitored counties, and Moderate on 15%. The median day sat at AQI 41; one day in ten went above 68.
The pollutant setting the AQI on an ordinary day here:
- ozone100%2,052 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 213 | 165 | 42 | 6 | 1 | 42 | 151 |
| 2024 | 209 | 178 | 25 | 6 | 1 | 40 | 177 |
| 2023 | 209 | 170 | 35 | 4 | 0 | 43 | 140 |
| 2022 | 212 | 173 | 33 | 6 | 0 | 40 | 147 |
| 2021 | 207 | 171 | 25 | 11 | 1 | 39 | 151 |
| 2020 | 208 | 182 | 24 | 2 | 0 | 39 | 129 |
| 2019 | 205 | 175 | 23 | 7 | 1 | 41 | 154 |
| 2018 | 208 | 168 | 32 | 8 | 0 | 40 | 126 |
| 2017 | 207 | 171 | 28 | 8 | 1 | 40 | 151 |
| 2016 | 174 | 125 | 36 | 13 | 2 | 44 | 187 |
| 2015 | 183 | 134 | 37 | 12 | 0 | 43 | 147 |
| 2014 | 182 | 140 | 31 | 11 | 1 | 43 | 151 |
| 2013 | 180 | 139 | 33 | 8 | 2 | 43 | 179 |
| 2012 | 179 | 129 | 35 | 15 | 2 | 44 | 182 |
| 2011 | 180 | 145 | 29 | 6 | 3 | 43 | 161 |
| 2010 | 179 | 124 | 46 | 9 | 1 | 44 | 151 |
*2025 may be a partial year in EPA's file.
Elsewhere in Connecticut
- Fairfield County20/yr
- New Haven County12/yr
- New London County7/yr
- Tolland County6/yr
- Hartford County5/yr
- Litchfield County4/yr
- Windham County2/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.