What Is the Air Quality in Plymouth, Massachusetts?
Plymouth, Massachusetts has an Air Quality Grade of C (fair) with a 5-year median AQI of 41. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
Plymouth, Massachusetts Air Quality Snapshot
| Air Quality Grade | C64/100 |
| 5-Year Median AQI | 41 (Good) |
| Most Recent Median AQI (2023) | 40 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Stable (+0.05 AQI/yr) |
| Unhealthy Days (last 5 yr) | 6 |
| National Rank (cleanest = #1) | #562 of 1,020 (55th most polluted percentile) |
| Massachusetts Rank | #8 of 13 |
What Does the C Grade Mean?
Plymouth, Massachusetts earns a C — air quality is fair, but not great. With a 5-year median AQI of 41, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Plymouth, Massachusetts's 5-year median AQI of 41 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within Massachusetts, Plymouth, Massachusetts's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 41.
For context within Massachusetts: Suffolk, Massachusetts currently holds the state's cleanest grade (B, AQI 44), while Middlesex, Massachusetts sits at the bottom (C, AQI 39).
What's in Plymouth, Massachusetts's Air?
The dominant pollutant in Plymouth, Massachusetts is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 210 | 58% |
| Fine Particulate Matter (PM2.5) | 155 | 42% |
Is the Air Getting Better or Worse?
Air quality in Plymouth, Massachusetts has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Plymouth, Massachusetts posted a median AQI of 44. By 2023 that figure was 40 — a drop of 4 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in Plymouth, Massachusetts
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 44 | 229 | 0 | PM2.5 |
| 2015 | 40 | 246 | 1 | PM2.5 |
| 2016 | 39 | 298 | 1 | Ozone |
| 2017 | 39 | 281 | 4 | Ozone |
| 2018 | 39 | 279 | 3 | Ozone |
| 2019 | 40 | 289 | 0 | Ozone |
| 2020 | 42 | 267 | 0 | PM2.5 |
| 2021 | 39 | 257 | 2 | PM2.5 |
| 2022 | 45 | 235 | 0 | PM2.5 |
| 2023 | 40 | 278 | 4 | Ozone |
Health Context for Plymouth, Massachusetts
Across the past five years, this area has logged just 6 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 1 days per year, or roughly one every other month. That is a low count by national standards.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
Plymouth, Massachusetts has an Air Quality Grade of C (fair) with a 5-year median AQI of 41. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.