Processed on 2024-03-04 13:21:48 PST.


Disclaimer: Data presented here come from a variety of sources and do not represent official EPA measurements. Please visit AirNow for official measurements.


Cumulative exposure to smoke is an important public health metric. This report summarizes the cumulative number of days air quality monitors in Massachusetts spent in each AQI category during the the month of May.

The tables below include only permanent monitors measuring PM2.5 and show cumulative exposure under existing NAAQS (National Ambient Air Quality Standards) and under the 2024 revised standards for PM2.5.

In the tables and plots below, ‘Old’ designates cumulative days calculated using the 2023 PM2.5 NAAQS while ‘New’ is calculated using the 2024 revised PM2.5 NAAQS. The impact of the NAAQS revision is quite clear.

May in Massachusetts

May 2014 – 9 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 256 9 0 0 0 0 23
New 221 44 0 0 0 0 23

May 2015 – 9 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 193 54 0 0 0 0 41
New 139 108 0 0 0 0 41

May 2016 – 20 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 203 31 0 0 0 0 54
New 197 37 0 0 0 0 54

May 2017 – 10 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 268 5 0 0 0 0 15
New 260 13 0 0 0 0 15

May 2018 – 24 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 255 40 0 0 0 0 57
New 185 110 0 0 0 0 57

May 2019 – 14 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 419 9 0 0 0 0 20
New 402 26 0 0 0 0 20

May 2020 – 28 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 387 2 0 0 0 0 27
New 358 31 0 0 0 0 27

May 2021 – 17 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 480 29 0 0 0 0 35
New 415 94 0 0 0 0 35

May 2022 – 17 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 471 18 0 0 0 0 23
New 436 53 0 0 0 0 23

May 2023 – 19 permanent monitors

Good Moderate USG Unhealthy Very Unhealthy Hazardous Missing
Old 519 37 0 0 0 0 20
New 446 110 0 0 0 0 20