EnviroNearby

Belknap County, New Hampshire air quality history

Daily Air Quality Index summaries from EPA monitors in Belknap, New Hampshire, 1996–2025.

89%
Good days in 2025
32
Median daily AQI, 2025
0
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Belknap, New Hampshire on 365 days. 324 of those days (89%) were in the Good range, and the median daily AQI was 32. That median is lower than the typical monitored county in New Hampshire (median 37 across 7 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 187 days. Across the years with fuller monitoring, the share of Good days fell: an average of 92% in 1996–1998 versus 86% in 2023–2025.

Years with fewer than 120 monitored days (2000) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1996: Good 184 of 197 days1996: Moderate 11 of 197 days1996: Unhealthy for Sensitive Groups 2 of 197 days19961997: Good 168 of 183 days1997: Moderate 13 of 183 days1997: Unhealthy for Sensitive Groups 1 of 183 days1997: Unhealthy 1 of 183 days1998: Good 195 of 213 days1998: Moderate 18 of 213 days1999: Good 175 of 216 days1999: Moderate 34 of 216 days1999: Unhealthy for Sensitive Groups 7 of 216 days2000: Good 8 of 15 days2000: Moderate 7 of 15 days2001: Good 126 of 186 days2001: Moderate 48 of 186 days2001: Unhealthy for Sensitive Groups 11 of 186 days2001: Unhealthy 1 of 186 days20012002: Good 156 of 211 days2002: Moderate 42 of 211 days2002: Unhealthy for Sensitive Groups 11 of 211 days2002: Unhealthy 2 of 211 days2003: Good 158 of 209 days2003: Moderate 45 of 209 days2003: Unhealthy for Sensitive Groups 6 of 209 days2004: Good 172 of 213 days2004: Moderate 38 of 213 days2004: Unhealthy for Sensitive Groups 3 of 213 days2005: Good 168 of 213 days2005: Moderate 39 of 213 days2005: Unhealthy for Sensitive Groups 6 of 213 days2006: Good 173 of 208 days2006: Moderate 33 of 208 days2006: Unhealthy for Sensitive Groups 2 of 208 days20062007: Good 173 of 213 days2007: Moderate 35 of 213 days2007: Unhealthy for Sensitive Groups 4 of 213 days2007: Unhealthy 1 of 213 days2008: Good 186 of 214 days2008: Moderate 27 of 214 days2008: Unhealthy for Sensitive Groups 1 of 214 days2009: Good 191 of 209 days2009: Moderate 18 of 209 days2010: Good 186 of 213 days2010: Moderate 24 of 213 days2010: Unhealthy for Sensitive Groups 3 of 213 days2011: Good 193 of 211 days2011: Moderate 18 of 211 days20112012: Good 179 of 210 days2012: Moderate 31 of 210 days2013: Good 200 of 213 days2013: Moderate 13 of 213 days2014: Good 201 of 213 days2014: Moderate 12 of 213 days2015: Good 201 of 213 days2015: Moderate 12 of 213 days2016: Good 230 of 257 days2016: Moderate 27 of 257 days20162017: Good 261 of 308 days2017: Moderate 47 of 308 days2018: Good 257 of 283 days2018: Moderate 26 of 283 days2019: Good 292 of 316 days2019: Moderate 24 of 316 days2020: Good 342 of 359 days2020: Moderate 17 of 359 days2021: Good 340 of 365 days2021: Moderate 24 of 365 days2021: Unhealthy for Sensitive Groups 1 of 365 days20212022: Good 339 of 358 days2022: Moderate 19 of 358 days2023: Good 310 of 365 days2023: Moderate 54 of 365 days2023: Unhealthy for Sensitive Groups 1 of 365 days2024: Good 311 of 365 days2024: Moderate 54 of 365 days2025: Good 324 of 365 days2025: Moderate 41 of 365 days2025
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001996: 90th percentile AQI 471997: 90th percentile AQI 481998: 90th percentile AQI 481999: 90th percentile AQI 622000: 90th percentile AQI 752001: 90th percentile AQI 932002: 90th percentile AQI 802003: 90th percentile AQI 672004: 90th percentile AQI 562005: 90th percentile AQI 662006: 90th percentile AQI 582007: 90th percentile AQI 612008: 90th percentile AQI 542009: 90th percentile AQI 502010: 90th percentile AQI 552011: 90th percentile AQI 492012: 90th percentile AQI 562013: 90th percentile AQI 482014: 90th percentile AQI 462015: 90th percentile AQI 462016: 90th percentile AQI 512017: 90th percentile AQI 542018: 90th percentile AQI 492019: 90th percentile AQI 482020: 90th percentile AQI 452021: 90th percentile AQI 472022: 90th percentile AQI 462023: 90th percentile AQI 542024: 90th percentile AQI 532025: 90th percentile AQI 511996: Median AQI 331997: Median AQI 351998: Median AQI 321999: Median AQI 362000: Median AQI 492001: Median AQI 442002: Median AQI 402003: Median AQI 402004: Median AQI 392005: Median AQI 392006: Median AQI 372007: Median AQI 382008: Median AQI 382009: Median AQI 332010: Median AQI 382011: Median AQI 352012: Median AQI 372013: Median AQI 322014: Median AQI 322015: Median AQI 332016: Median AQI 352017: Median AQI 342018: Median AQI 332019: Median AQI 322020: Median AQI 322021: Median AQI 312022: Median AQI 322023: Median AQI 352024: Median AQI 352025: Median AQI 321996200120062011201620212025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Ozone18751%
Fine particles (PM2.5)17849%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365324410000325192Ozone
2024365311540000355378PM2.5
20233653105410003554105PM2.5
2022358339190000324668Ozone
20213653402410003147110PM2.5
2020359342170000324565PM2.5
2019316292240000324877PM2.5
2018283257260000334980Ozone
2017308261470000345484Ozone
2016257230270000355184Ozone
2015213201120000334690Ozone
2014213201120000324690Ozone
2013213200130000324884Ozone
2012210179310000375697Ozone
2011211193180000354993Ozone
20102131862430003855119Ozone
2009209191180000335097Ozone
20082141862710003854101Ozone
20072131733541003861156Ozone
20062081733320003758112Ozone
20052131683960003966129Ozone
20042131723830003956143Ozone
20032091584560004067147Ozone
200221115642112004080161Ozone
200118612648111004493190Ozone
200015870000497579PM2.5
19992161753470003662145Ozone
19982131951800003248100Ozone
19971831681311003548154Ozone
19961971841120003347126Ozone

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in New Hampshire with a similar median AQI in 2025

All monitored counties in New Hampshire

Source: U.S. EPA AirData, “Annual AQI by County” files for 1996–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem