Median AQI
32
Good
New Hampshire · County air quality · 2025
Belknap County, New Hampshire
Median AQI 32 (Good). 88.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 32
- Median AQI
- 88.8%
- Good-air days
- 0
- Unhealthy days
- 77%
- Cleaner than US counties
Belknap County's 2025 annual median AQI is 32 (Good), with 88.8% Good days
According to the U.S. EPA Air Quality System, Belknap County, New Hampshire posted a 2025 median AQI of 32 (Good) across 365 monitored days, with 88.8% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Belknap County's 88.8% Good-day share places it cleaner than 77% of US counties in 2025.
- Closest median-AQI peer
- Aroostook County (83.3% Good, median AQI 32) is the closest nationwide median-AQI peer to Belknap County.
- 2020–2025 trend
- Belknap County's floor-qualifying Good-day share is worsening from 2020 to 2025 (95.3% → 88.8%).
- Median AQI
- Median AQI: 32
The verdict
According to EPA Air Quality System monitoring data, Belknap County's air is good on balance, cleaner than most US counties, a median AQI of 32 with 88.8% of 365 monitored days in the Good band, driven mainly by Ozone.
- 32
- median AQI · Good
- 88.8%
- days rated Good
- Ozone
- main pollutant
- 77%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 92.
Annual release change
What changed in the 2025 EPA annual release
- Belknap County's Good-day share rose from 85.2% to 88.8% between the 2024 and 2025 EPA annual releases, a change of +3.6 percentage points.
- Belknap County's peak single-day AQI rose from 78 to 92 between the 2024 and 2025 EPA annual releases, a change of +14 points.
- Belknap County's median AQI fell from 35 to 32 between the 2024 and 2025 EPA annual releases, a change of -3 points.
Data updated August 2026
- Good · 324 d · 88.8%
- Moderate · 41 d · 11.2%
How did Belknap County's air break down in 2025?
Across 365 monitored days, 324 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 92 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 32 (Good).
Insights: Belknap County, New Hampshire. EPA monitors recorded a median Air Quality Index of 32 across 365 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 324 (89%) fell in the Good band (AQI 0–50), 41 (11%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 51, while the worst single-day peak hit 92 (Moderate). Residents averaged about 26.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (187 days), PM2.5 (178 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -6.5 points and the median AQI moved +0 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 92, moderate but never Unhealthy. Nearby counties show comparable readings: Cheshire (78.9% good, AQI 37); Coos (81.5% good, AQI 44); Grafton (83.6% good, AQI 36); Hillsborough (84.9% good, AQI 38); Merrimack (96.7% good, AQI 37); Rockingham (84.7% good, AQI 38).
Air Quality Summary
Good Days
88.8%
324 of 365 monitored days
13.8pp vs 75% target
Max AQI Recorded
92
Moderate
Health Grade
Good
90th-pct AQI 51
Belknap County, Good days share 88.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Belknap 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 365 monitored days across EPA AQI categories.
Good
324
89%
Moderate
41
11%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Belknap County.
- Ozone · 187 days · 51.2%
- PM2.5 · 178 days · 48.8%
Health Impact Assessment
Good
Belknap County's air quality is rated Good based on 88.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 88.8% of monitored days in 2025, with a median AQI of 32. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 187 of 365 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Belknap County. Highest Good-day share: 2020 (95.3%, 342 of 359 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 342 | 17 | 0 | 0 | 32 | 65 |
| 2021 | 340 | 24 | 1 | 0 | 31 | 110 |
| 2022 | 339 | 19 | 0 | 0 | 32 | 68 |
| 2023 | 310 | 54 | 1 | 0 | 35 | 105 |
| 2024 | 311 | 54 | 0 | 0 | 35 | 78 |
| 2025 | 324 | 41 | 0 | 0 | 32 | 92 |
How does Belknap County compare?
How Belknap County compares
Good-day share better than typical
Belknap County 88.8%
Aroostook County, Maine 83.3%
Typical US county 76.0%
Median AQI better than typical
Belknap County 32
Aroostook County, Maine 32
Typical US county 39
Unhealthy days / yr better than typical
Belknap County 0
Aroostook County, Maine 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Belknap County (32), not geographic neighbors.
Aroostook County, Maine
Median AQI 32 · 83.3% Good-day share
Carter County, Oklahoma
Median AQI 32 · 81.6% Good-day share
Del Norte County, California
Median AQI 32 · 81.8% Good-day share
Hawaii County, Hawaii
Median AQI 32 · 86.0% Good-day share
Macon County, North Carolina
Median AQI 32 · 96.5% Good-day share
Montgomery County, Tennessee
Median AQI 32 · 83.8% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Pike County, Georgia
88.9% Good-day share · median AQI 38
Williamson County, Tennessee
88.9% Good-day share · median AQI 40
Livingston County, Kentucky
88.6% Good-day share · median AQI 40
Haywood County, North Carolina
89.0% Good-day share · median AQI 43
Darlington County, South Carolina
89.0% Good-day share · median AQI 40
Chautauqua County, New York
89.0% Good-day share · median AQI 36
New Hampshire counties on the map
Geographic containment only, other monitored counties in New Hampshire, independent of AQI or pollutant match.
What Belknap 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 32 means for exposure. Health guidance
- See how Belknap County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Belknap County with its New Hampshire neighbours before drawing a conclusion about the region. All of New Hampshire
Based on 365 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Belknap County, New Hampshire? ▼
Belknap County has a median Air Quality Index (AQI) of 32, rated "Good." 88.8% of monitored days (324 out of 365) had good air quality in 2025.
What is the main pollutant in Belknap County? ▼
The primary pollutant in Belknap County is Ozone (O3), which was the main AQI driver on 187 days (51% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Belknap County have? ▼
In 2025, Belknap County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 92.
Is the air quality in Belknap County getting better or worse? ▼
Air quality in Belknap County is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 95.3% (342 of 359 days). Lowest qualifying Good-day share: 2023 at 84.9% (310 of 365 days).
What does AQI 32 mean for health? ▼
Belknap County's median AQI of 32 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Belknap County compare to other counties in New Hampshire? ▼
Belknap County has 88.8% good air days. Nearby counties in New Hampshire: Cheshire (78.9% good), Coos (81.5% good), Grafton (83.6% good), Hillsborough (84.9% good), Merrimack (96.7% good), Rockingham (84.7% good).
What is the 90th percentile AQI in Belknap County? ▼
The 90th percentile AQI for Belknap County is 51, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 92 (Moderate).
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Belknap County, New Hampshire · 2020–2025
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Every figure on PlainAirData 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.