What Is the Air Quality in Coos, New Hampshire?
Coos, New Hampshire has an Air Quality Grade of B (good) with a 5-year median AQI of 42. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
Coos, New Hampshire Air Quality Snapshot
| Air Quality Grade | B67/100 |
| 5-Year Median AQI | 42 (Good) |
| Most Recent Median AQI (2023) | 43 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Stable (-0.30 AQI/yr) |
| Unhealthy Days (last 5 yr) | 6 |
| National Rank (cleanest = #1) | #581 of 1,020 (57th most polluted percentile) |
| New Hampshire Rank | #7 of 7 |
What Does the B Grade Mean?
Coos, New Hampshire earns a B — air quality is reliably in the safe range for most residents most of the time, with a 5-year median AQI of 42. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Coos, New Hampshire's 5-year median AQI of 42 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within New Hampshire, Coos, New Hampshire runs more polluted than the state average of 38 — local sources or geography are concentrating pollution above the state's typical reading.
For context within New Hampshire: Rockingham, New Hampshire currently holds the state's cleanest grade (B, AQI 40), while Merrimack, New Hampshire sits at the bottom (C, AQI 37).
What's in Coos, New Hampshire's Air?
The dominant pollutant in Coos, New Hampshire is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 358 | 98% |
| Fine Particulate Matter (PM2.5) | 6 | 2% |
Is the Air Getting Better or Worse?
Air quality in Coos, New Hampshire 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, Coos, New Hampshire posted a median AQI of 43. By 2023 that figure was 43 — a flat reading of 0 AQI points across 10 years of EPA records.
Year-by-Year AQI in Coos, New Hampshire
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 43 | 311 | 0 | Ozone |
| 2015 | 45 | 285 | 7 | Ozone |
| 2016 | 44 | 303 | 4 | Ozone |
| 2017 | 43 | 290 | 3 | Ozone |
| 2018 | 44 | 222 | 3 | Ozone |
| 2019 | 40 | 313 | 0 | Ozone |
| 2020 | 43 | 339 | 0 | Ozone |
| 2021 | 42 | 325 | 2 | Ozone |
| 2022 | 40 | 350 | 0 | Ozone |
| 2023 | 43 | 318 | 4 | Ozone |
Health Context for Coos, New Hampshire
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.
For most healthy adults, current air quality in this area does not require any change in behavior. People with severe asthma, COPD, or recent cardiac events should still keep an eye on daily AQI alerts, especially during wildfire season. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
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.
Coos, New Hampshire has an Air Quality Grade of B (good) with a 5-year median AQI of 42. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
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.