EnviroNearby

Hillsborough County, New Hampshire air quality history

Daily Air Quality Index summaries from EPA monitors in Hillsborough, New Hampshire, 1980–2025.

85%
Good days in 2025
38
Median daily AQI, 2025
4
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 Hillsborough, New Hampshire on 365 days. 310 of those days (85%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in New Hampshire (median 37 across 7 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 308 days. Across the years with fuller monitoring, the share of Good days rose: an average of 28% in 1980–1982 versus 86% in 2023–2025.

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%1980: Good 143 of 364 days1980: Moderate 186 of 364 days1980: Unhealthy for Sensitive Groups 21 of 364 days1980: Unhealthy 12 of 364 days1980: Very Unhealthy 2 of 364 days19801981: Good 92 of 365 days1981: Moderate 230 of 365 days1981: Unhealthy for Sensitive Groups 30 of 365 days1981: Unhealthy 9 of 365 days1981: Very Unhealthy 4 of 365 days1982: Good 67 of 365 days1982: Moderate 260 of 365 days1982: Unhealthy for Sensitive Groups 31 of 365 days1982: Unhealthy 6 of 365 days1982: Very Unhealthy 1 of 365 days1983: Good 111 of 365 days1983: Moderate 218 of 365 days1983: Unhealthy for Sensitive Groups 30 of 365 days1983: Unhealthy 5 of 365 days1983: Very Unhealthy 1 of 365 days1984: Good 162 of 366 days1984: Moderate 164 of 366 days1984: Unhealthy for Sensitive Groups 22 of 366 days1984: Unhealthy 16 of 366 days1984: Very Unhealthy 2 of 366 days1985: Good 87 of 365 days1985: Moderate 248 of 365 days1985: Unhealthy for Sensitive Groups 24 of 365 days1985: Unhealthy 6 of 365 days19851986: Good 141 of 365 days1986: Moderate 201 of 365 days1986: Unhealthy for Sensitive Groups 14 of 365 days1986: Unhealthy 9 of 365 days1987: Good 231 of 365 days1987: Moderate 110 of 365 days1987: Unhealthy for Sensitive Groups 22 of 365 days1987: Unhealthy 2 of 365 days1988: Good 210 of 366 days1988: Moderate 114 of 366 days1988: Unhealthy for Sensitive Groups 28 of 366 days1988: Unhealthy 9 of 366 days1988: Very Unhealthy 5 of 366 days1989: Good 253 of 365 days1989: Moderate 97 of 365 days1989: Unhealthy for Sensitive Groups 14 of 365 days1989: Unhealthy 1 of 365 days1990: Good 267 of 365 days1990: Moderate 76 of 365 days1990: Unhealthy for Sensitive Groups 19 of 365 days1990: Unhealthy 3 of 365 days19901991: Good 289 of 365 days1991: Moderate 56 of 365 days1991: Unhealthy for Sensitive Groups 12 of 365 days1991: Unhealthy 7 of 365 days1991: Very Unhealthy 1 of 365 days1992: Good 308 of 366 days1992: Moderate 45 of 366 days1992: Unhealthy for Sensitive Groups 8 of 366 days1992: Unhealthy 5 of 366 days1993: Good 304 of 365 days1993: Moderate 44 of 365 days1993: Unhealthy for Sensitive Groups 13 of 365 days1993: Unhealthy 4 of 365 days1994: Good 277 of 364 days1994: Moderate 68 of 364 days1994: Unhealthy for Sensitive Groups 16 of 364 days1994: Unhealthy 3 of 364 days1995: Good 308 of 364 days1995: Moderate 35 of 364 days1995: Unhealthy for Sensitive Groups 15 of 364 days1995: Unhealthy 6 of 364 days19951996: Good 280 of 366 days1996: Moderate 73 of 366 days1996: Unhealthy for Sensitive Groups 9 of 366 days1996: Unhealthy 4 of 366 days1997: Good 318 of 365 days1997: Moderate 34 of 365 days1997: Unhealthy for Sensitive Groups 9 of 365 days1997: Unhealthy 3 of 365 days1997: Very Unhealthy 1 of 365 days1998: Good 314 of 365 days1998: Moderate 41 of 365 days1998: Unhealthy for Sensitive Groups 7 of 365 days1998: Unhealthy 3 of 365 days1999: Good 256 of 357 days1999: Moderate 80 of 357 days1999: Unhealthy for Sensitive Groups 13 of 357 days1999: Unhealthy 8 of 357 days2000: Good 285 of 366 days2000: Moderate 78 of 366 days2000: Unhealthy for Sensitive Groups 2 of 366 days2000: Unhealthy 1 of 366 days20002001: Good 264 of 365 days2001: Moderate 82 of 365 days2001: Unhealthy for Sensitive Groups 13 of 365 days2001: Unhealthy 5 of 365 days2001: Very Unhealthy 1 of 365 days2002: Good 270 of 365 days2002: Moderate 68 of 365 days2002: Unhealthy for Sensitive Groups 18 of 365 days2002: Unhealthy 5 of 365 days2002: Very Unhealthy 4 of 365 days2003: Good 256 of 365 days2003: Moderate 94 of 365 days2003: Unhealthy for Sensitive Groups 15 of 365 days2004: Good 269 of 366 days2004: Moderate 86 of 366 days2004: Unhealthy for Sensitive Groups 8 of 366 days2004: Unhealthy 3 of 366 days2005: Good 258 of 365 days2005: Moderate 88 of 365 days2005: Unhealthy for Sensitive Groups 15 of 365 days2005: Unhealthy 4 of 365 days20052006: Good 278 of 365 days2006: Moderate 74 of 365 days2006: Unhealthy for Sensitive Groups 12 of 365 days2006: Unhealthy 1 of 365 days2007: Good 273 of 365 days2007: Moderate 74 of 365 days2007: Unhealthy for Sensitive Groups 16 of 365 days2007: Unhealthy 2 of 365 days2008: Good 268 of 366 days2008: Moderate 88 of 366 days2008: Unhealthy for Sensitive Groups 9 of 366 days2008: Unhealthy 1 of 366 days2009: Good 303 of 365 days2009: Moderate 57 of 365 days2009: Unhealthy for Sensitive Groups 5 of 365 days2010: Good 287 of 365 days2010: Moderate 70 of 365 days2010: Unhealthy for Sensitive Groups 8 of 365 days20102011: Good 296 of 365 days2011: Moderate 66 of 365 days2011: Unhealthy for Sensitive Groups 2 of 365 days2011: Unhealthy 1 of 365 days2012: Good 296 of 366 days2012: Moderate 64 of 366 days2012: Unhealthy for Sensitive Groups 6 of 366 days2013: Good 280 of 365 days2013: Moderate 84 of 365 days2013: Unhealthy for Sensitive Groups 1 of 365 days2014: Good 300 of 365 days2014: Moderate 64 of 365 days2014: Unhealthy for Sensitive Groups 1 of 365 days2015: Good 289 of 365 days2015: Moderate 74 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days20152016: Good 324 of 366 days2016: Moderate 39 of 366 days2016: Unhealthy for Sensitive Groups 3 of 366 days2017: Good 336 of 365 days2017: Moderate 28 of 365 days2017: Unhealthy for Sensitive Groups 1 of 365 days2018: Good 327 of 365 days2018: Moderate 38 of 365 days2019: Good 345 of 365 days2019: Moderate 20 of 365 days2020: Good 351 of 366 days2020: Moderate 15 of 366 days20202021: Good 328 of 365 days2021: Moderate 35 of 365 days2021: Unhealthy for Sensitive Groups 2 of 365 days2022: Good 329 of 365 days2022: Moderate 36 of 365 days2023: Good 305 of 365 days2023: Moderate 55 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2024: Good 328 of 366 days2024: Moderate 38 of 366 days2025: Good 310 of 365 days2025: Moderate 51 of 365 days2025: Unhealthy for Sensitive Groups 4 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 year0501001501980: 90th percentile AQI 1001981: 90th percentile AQI 1151982: 90th percentile AQI 1011983: 90th percentile AQI 1001984: 90th percentile AQI 1081985: 90th percentile AQI 951986: 90th percentile AQI 831987: 90th percentile AQI 841988: 90th percentile AQI 1031989: 90th percentile AQI 801990: 90th percentile AQI 861991: 90th percentile AQI 781992: 90th percentile AQI 691993: 90th percentile AQI 661994: 90th percentile AQI 801995: 90th percentile AQI 711996: 90th percentile AQI 671997: 90th percentile AQI 541998: 90th percentile AQI 581999: 90th percentile AQI 752000: 90th percentile AQI 662001: 90th percentile AQI 772002: 90th percentile AQI 812003: 90th percentile AQI 782004: 90th percentile AQI 712005: 90th percentile AQI 762006: 90th percentile AQI 642007: 90th percentile AQI 802008: 90th percentile AQI 692009: 90th percentile AQI 582010: 90th percentile AQI 672011: 90th percentile AQI 582012: 90th percentile AQI 642013: 90th percentile AQI 582014: 90th percentile AQI 552015: 90th percentile AQI 562016: 90th percentile AQI 522017: 90th percentile AQI 482018: 90th percentile AQI 512019: 90th percentile AQI 472020: 90th percentile AQI 462021: 90th percentile AQI 512022: 90th percentile AQI 502023: 90th percentile AQI 582024: 90th percentile AQI 512025: 90th percentile AQI 551980: Median AQI 561981: Median AQI 641982: Median AQI 671983: Median AQI 601984: Median AQI 531985: Median AQI 631986: Median AQI 561987: Median AQI 441988: Median AQI 471989: Median AQI 421990: Median AQI 401991: Median AQI 381992: Median AQI 351993: Median AQI 351994: Median AQI 391995: Median AQI 321996: Median AQI 411997: Median AQI 351998: Median AQI 341999: Median AQI 402000: Median AQI 352001: Median AQI 412002: Median AQI 382003: Median AQI 412004: Median AQI 372005: Median AQI 412006: Median AQI 342007: Median AQI 372008: Median AQI 392009: Median AQI 362010: Median AQI 392011: Median AQI 392012: Median AQI 402013: Median AQI 402014: Median AQI 412015: Median AQI 412016: Median AQI 372017: Median AQI 372018: Median AQI 372019: Median AQI 372020: Median AQI 372021: Median AQI 372022: Median AQI 392023: Median AQI 392024: Median AQI 372025: Median AQI 381980198519901995200020052010201520202025
  • 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
Ozone30884%
Fine particles (PM2.5)5716%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253653105140003855123Ozone
2024366328380000375197Ozone
20233653055550003958119Ozone
20223653293600003950100Ozone
20213653283520003751144Ozone
2020366351150000374690Ozone
2019365345200000374780Ozone
2018365327380000375197Ozone
20173653362810003748101Ozone
20163663243930003752108Ozone
20153652897420004156129Ozone
20143653006410004155129Ozone
20133652808410004058112Ozone
20123662966460004064150Ozone
20113652966621003958161Ozone
20103652877080003967140Ozone
20093653035750003658112Ozone
20083662688891003969154Ozone
200736527374162003780172Ozone
200636527874121003464151Ozone
200536525888154004176177Ozone
20043662698683003771179Ozone
200336525694150004178150Ozone
200236527068185403881206Ozone
200136526482135104177205Ozone
20003662857821003566161Ozone
199935725680138004075161Ozone
19983653144173003458177Ozone
19973653183493103554202Ozone
19963662807394004167168Ozone
199536430835156003271187Ozone
199436427768163003980166Ozone
199336530444134003566190Ozone
19923663084585003569169Ozone
199136528956127103878206Ozone
199036526776193004086177Ozone
198936525397141004280187NO2
19883662101142895047103217NO2
1987365231110222004484179CO
1986365141201149005683179CO
198536587248246006395174CO
198436616216422162053108205CO
19833651112183051060100212CO
1982365672603161067101208CO
1981365922303094064115220CO
198036414318621122056100208CO

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 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem