Median AQI
40
Good
New Hampshire · County air quality · 2025
Coos County, New Hampshire
Median AQI 40 (Good). 85.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 40
- Median AQI
- 85.4%
- Good-air days
- 0
- Unhealthy days
- 67%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Coos County's air is good on balance, cleaner than the median US county, a median AQI of 40 with 85.4% of 274 monitored days in the Good band, driven mainly by Ozone.
- 40
- median AQI · Good
- 85.4%
- days rated Good
- Ozone
- main pollutant
- 67%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 119.
Data updated July 2026
- Good · 234 d · 85.4%
- Moderate · 36 d · 13.1%
- USG · 4 d · 1.5%
How did Coos County's air break down in 2025?
Across 274 monitored days, 234 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 119 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 274 days monitored. Median AQI: 40 (Good).
Insights: Coos County, New Hampshire. EPA monitors recorded a median Air Quality Index of 40 across 274 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 234 (85%) fell in the Good band (AQI 0–50), 36 (13%) registered Moderate readings, and 4 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 58, while the worst single-day peak hit 119 (USG). Residents averaged about 25.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (180 days), CO (94 days). Across the 2020–2025 trend window, good days shifted by -105 and the median AQI moved -3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 119, usg but never Unhealthy. Nearby counties show comparable readings: Belknap (87.9% good, AQI 34); Cheshire (76.9% good, AQI 38); Grafton (81.3% good, AQI 38); Hillsborough (82.5% good, AQI 38); Merrimack (95.9% good, AQI 38); Rockingham (82.5% good, AQI 39).
Air Quality Summary
Good Days
85.4%
234 of 274 monitored days
10.4pp vs 75% target
Max AQI Recorded
119
USG
Health Grade
Good
90th-pct AQI 58
Coos County, Good days share 85.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Coos County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 274 monitored days across EPA AQI categories.
Good
234
85%
Moderate
36
13%
USG
4
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Coos County.
- Ozone · 180 days · 65.7%
- CO · 94 days · 34.3%
Health Impact Assessment
Good
Coos County's air quality is rated Good based on 85.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 85.4% of monitored days in 2025, with a median AQI of 40. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 180 of 274 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Coos County. Best year: 2022 (350 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 339 | 27 | 0 | 0 | 43 | 74 |
| 2021 | 325 | 33 | 2 | 0 | 42 | 133 |
| 2022 | 350 | 9 | 0 | 0 | 40 | 64 |
| 2023 | 318 | 42 | 4 | 0 | 43 | 136 |
| 2024 | 296 | 69 | 0 | 0 | 44 | 90 |
| 2025 | 234 | 36 | 4 | 0 | 40 | 119 |
How does Coos County compare?
How Coos County compares
Good-day share better than US avg
Coos County 85.4%
Belknap County, New Hampshire 87.9%
US average 76.5%
Median AQI worse than US avg
Coos County 40
Belknap County, New Hampshire 34
US average 38
Unhealthy days / yr about average
Coos County 0
Belknap County, New Hampshire 0
US average 0
Other Counties in New Hampshire
Air quality comparison for nearby counties in New Hampshire.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Coos County.
Amador County, California
AQI 40 · 84.8% good
Anne Arundel County, Maryland
AQI 40 · 87.2% good
Arlington County, Virginia
AQI 40 · 84.8% good
Bergen County, New Jersey
AQI 40 · 71.1% good
Berkeley County, West Virginia
AQI 40 · 81.1% good
Billings County, North Dakota
AQI 40 · 80.3% good
What Coos County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 40 means for exposure. Health guidance
- See how Coos County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Coos County with its New Hampshire neighbours before drawing a conclusion about the region. All of New Hampshire
Based on 274 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Coos County, New Hampshire? ▼
Coos County has a median Air Quality Index (AQI) of 40, rated "Good." 85.4% of monitored days (234 out of 274) had good air quality in 2025.
What is the main pollutant in Coos County? ▼
The primary pollutant in Coos County is Ozone (O3), which was the main AQI driver on 180 days (66% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Coos County have? ▼
In 2025, Coos County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 119.
Is the air quality in Coos County getting better or worse? ▼
Air quality in Coos County is worsening based on 5-year trends (2020-2025). Best year: 2022 with 350 good days. Worst year: 2025 with 234 good days.
What does AQI 40 mean for health? ▼
Coos County's median AQI of 40 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Coos County compare to other counties in New Hampshire? ▼
Coos County has 85.4% good air days. Nearby counties in New Hampshire: Belknap (87.9% good), Cheshire (76.9% good), Grafton (81.3% good), Hillsborough (82.5% good), Merrimack (95.9% good), Rockingham (82.5% good).
What is the 90th percentile AQI in Coos County? ▼
The 90th percentile AQI for Coos County is 58, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 119 (USG).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.