Bad Air Days in Essex County, Massachusetts: 3 a Year
3 bad air days a year
About the middle of monitored US counties. Ranked 419 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (27% particle days).
Which months to watch
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in July and May and August. Averaged over 2016 to 2025.
What to buy, and what not to
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
The worst days on file
In 2000 to 2009 this county averaged 17 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2022, with 5 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2024-11-10 | 1513 | PM2.5 |
| 2024-11-09 | 493 | PM2.5 |
| 2024-10-29 | 162 | PM2.5 |
| 2024-11-08 | 157 | PM2.5 |
| 2017-05-17 | 136 | Ozone |
Most days, not the worst ones
Across 3,652 monitored days from 2016 to 2025, the air in Essex County rated Good on 77% of them, more often than the 72% typical of monitored counties, and Moderate on 22%. The median day sat at AQI 40; one day in ten went above 57.
The pollutant setting the AQI on an ordinary day here:
- ozone57%2,095 days
- fine particles (PM2.5)42%1,548 days
Essex County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 296 | 66 | 3 | 0 | 40 | 136 |
| 2024 | 366 | 300 | 62 | 4 | 4 | 37 | 1513 |
| 2023 | 365 | 243 | 120 | 2 | 0 | 44 | 105 |
| 2022 | 365 | 276 | 84 | 5 | 0 | 41 | 113 |
| 2021 | 365 | 285 | 79 | 1 | 0 | 38 | 129 |
| 2020 | 366 | 282 | 84 | 0 | 0 | 40 | 97 |
| 2019 | 364 | 288 | 75 | 1 | 0 | 41 | 122 |
| 2018 | 365 | 263 | 98 | 4 | 0 | 42 | 115 |
| 2017 | 365 | 285 | 77 | 3 | 0 | 40 | 136 |
| 2016 | 366 | 295 | 68 | 3 | 0 | 39 | 105 |
| 2015 | 365 | 255 | 107 | 3 | 0 | 41 | 122 |
| 2014 | 365 | 244 | 120 | 1 | 0 | 43 | 108 |
| 2013 | 365 | 216 | 141 | 8 | 0 | 45 | 126 |
| 2012 | 366 | 206 | 151 | 9 | 1 | 47 | 164 |
| 2011 | 365 | 179 | 182 | 4 | 1 | 51 | 151 |
| 2010 | 365 | 222 | 137 | 6 | 1 | 44 | 157 |
*2025 may be a partial year in EPA's file.
Elsewhere in Massachusetts
- Bristol County4/yr
- Hampden County3/yr
- Dukes County2/yr
- Barnstable County2/yr
- Hampshire County2/yr
- Norfolk County2/yr
- Worcester County2/yr
- Plymouth 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.