EnviroNearby

Barnstable County, Massachusetts air quality history

Daily Air Quality Index summaries from EPA monitors in Barnstable, Massachusetts, 1987–2025.

94%
Good days in 2025
36
Median daily AQI, 2025
3
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Barnstable, Massachusetts on 364 days. 341 of those days (94%) were in the Good range, and the median daily AQI was 36. That median is about the same as the typical monitored county in Massachusetts (median 38 across 13 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 357 days. Across the years with fuller monitoring, the share of Good days rose: an average of 64% in 1987–1989 versus 93% 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%1987: Good 128 of 178 days1987: Moderate 38 of 178 days1987: Unhealthy for Sensitive Groups 6 of 178 days1987: Unhealthy 5 of 178 days1987: Very Unhealthy 1 of 178 days19871988: Good 120 of 204 days1988: Moderate 35 of 204 days1988: Unhealthy for Sensitive Groups 25 of 204 days1988: Unhealthy 12 of 204 days1988: Very Unhealthy 12 of 204 days1989: Good 120 of 193 days1989: Moderate 44 of 193 days1989: Unhealthy for Sensitive Groups 21 of 193 days1989: Unhealthy 6 of 193 days1989: Very Unhealthy 2 of 193 days1990: Good 154 of 209 days1990: Moderate 36 of 209 days1990: Unhealthy for Sensitive Groups 11 of 209 days1990: Unhealthy 7 of 209 days1990: Very Unhealthy 1 of 209 days1991: Good 133 of 198 days1991: Moderate 31 of 198 days1991: Unhealthy for Sensitive Groups 18 of 198 days1991: Unhealthy 10 of 198 days1991: Very Unhealthy 6 of 198 days1992: Good 157 of 213 days1992: Moderate 37 of 213 days1992: Unhealthy for Sensitive Groups 13 of 213 days1992: Unhealthy 4 of 213 days1992: Very Unhealthy 2 of 213 days19921993: Good 148 of 195 days1993: Moderate 31 of 195 days1993: Unhealthy for Sensitive Groups 12 of 195 days1993: Unhealthy 4 of 195 days1994: Good 148 of 210 days1994: Moderate 45 of 210 days1994: Unhealthy for Sensitive Groups 13 of 210 days1994: Unhealthy 4 of 210 days1995: Good 157 of 213 days1995: Moderate 32 of 213 days1995: Unhealthy for Sensitive Groups 16 of 213 days1995: Unhealthy 5 of 213 days1995: Very Unhealthy 3 of 213 days1996: Good 147 of 212 days1996: Moderate 46 of 212 days1996: Unhealthy for Sensitive Groups 11 of 212 days1996: Unhealthy 6 of 212 days1996: Very Unhealthy 2 of 212 days1997: Good 158 of 217 days1997: Moderate 28 of 217 days1997: Unhealthy for Sensitive Groups 15 of 217 days1997: Unhealthy 14 of 217 days1997: Very Unhealthy 2 of 217 days19971998: Good 283 of 364 days1998: Moderate 60 of 364 days1998: Unhealthy for Sensitive Groups 19 of 364 days1998: Unhealthy 1 of 364 days1998: Very Unhealthy 1 of 364 days1999: Good 217 of 272 days1999: Moderate 32 of 272 days1999: Unhealthy for Sensitive Groups 11 of 272 days1999: Unhealthy 10 of 272 days1999: Very Unhealthy 2 of 272 days2000: Good 220 of 275 days2000: Moderate 41 of 275 days2000: Unhealthy for Sensitive Groups 11 of 275 days2000: Unhealthy 2 of 275 days2000: Very Unhealthy 1 of 275 days2001: Good 293 of 365 days2001: Moderate 46 of 365 days2001: Unhealthy for Sensitive Groups 13 of 365 days2001: Unhealthy 10 of 365 days2001: Very Unhealthy 3 of 365 days2002: Good 227 of 298 days2002: Moderate 46 of 298 days2002: Unhealthy for Sensitive Groups 16 of 298 days2002: Unhealthy 8 of 298 days2002: Very Unhealthy 1 of 298 days20022003: Good 162 of 231 days2003: Moderate 45 of 231 days2003: Unhealthy for Sensitive Groups 16 of 231 days2003: Unhealthy 7 of 231 days2003: Very Unhealthy 1 of 231 days2004: Good 186 of 241 days2004: Moderate 44 of 241 days2004: Unhealthy for Sensitive Groups 9 of 241 days2004: Unhealthy 1 of 241 days2004: Very Unhealthy 1 of 241 days2005: Good 159 of 233 days2005: Moderate 56 of 233 days2005: Unhealthy for Sensitive Groups 11 of 233 days2005: Unhealthy 7 of 233 days2006: Good 173 of 243 days2006: Moderate 53 of 243 days2006: Unhealthy for Sensitive Groups 14 of 243 days2006: Unhealthy 2 of 243 days2006: Very Unhealthy 1 of 243 days2007: Good 170 of 233 days2007: Moderate 47 of 233 days2007: Unhealthy for Sensitive Groups 15 of 233 days2007: Unhealthy 1 of 233 days20072008: Good 179 of 239 days2008: Moderate 52 of 239 days2008: Unhealthy for Sensitive Groups 6 of 239 days2008: Unhealthy 1 of 239 days2008: Very Unhealthy 1 of 239 days2009: Good 198 of 237 days2009: Moderate 35 of 237 days2009: Unhealthy for Sensitive Groups 4 of 237 days2010: Good 221 of 267 days2010: Moderate 39 of 267 days2010: Unhealthy for Sensitive Groups 6 of 267 days2010: Unhealthy 1 of 267 days2011: Good 246 of 275 days2011: Moderate 26 of 275 days2011: Unhealthy for Sensitive Groups 3 of 275 days2012: Good 223 of 258 days2012: Moderate 28 of 258 days2012: Unhealthy for Sensitive Groups 6 of 258 days2012: Unhealthy 1 of 258 days20122013: Good 288 of 315 days2013: Moderate 23 of 315 days2013: Unhealthy for Sensitive Groups 4 of 315 days2014: Good 347 of 363 days2014: Moderate 16 of 363 days2015: Good 289 of 317 days2015: Moderate 24 of 317 days2015: Unhealthy for Sensitive Groups 4 of 317 days2016: Good 334 of 362 days2016: Moderate 27 of 362 days2016: Unhealthy for Sensitive Groups 1 of 362 days2017: Good 332 of 358 days2017: Moderate 21 of 358 days2017: Unhealthy for Sensitive Groups 5 of 358 days20172018: Good 335 of 360 days2018: Moderate 21 of 360 days2018: Unhealthy for Sensitive Groups 4 of 360 days2019: Good 346 of 359 days2019: Moderate 13 of 359 days2020: Good 339 of 351 days2020: Moderate 10 of 351 days2020: Unhealthy for Sensitive Groups 2 of 351 days2021: Good 331 of 359 days2021: Moderate 25 of 359 days2021: Unhealthy for Sensitive Groups 3 of 359 days2022: Good 341 of 360 days2022: Moderate 19 of 360 days20222023: Good 331 of 358 days2023: Moderate 24 of 358 days2023: Unhealthy for Sensitive Groups 3 of 358 days2024: Good 333 of 353 days2024: Moderate 19 of 353 days2024: Unhealthy for Sensitive Groups 1 of 353 days2025: Good 341 of 364 days2025: Moderate 20 of 364 days2025: Unhealthy for Sensitive Groups 3 of 364 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 year0501001502001987: 90th percentile AQI 901988: 90th percentile AQI 1641989: 90th percentile AQI 1221990: 90th percentile AQI 971991: 90th percentile AQI 1401992: 90th percentile AQI 1001993: 90th percentile AQI 931994: 90th percentile AQI 931995: 90th percentile AQI 1081996: 90th percentile AQI 1001997: 90th percentile AQI 1261998: 90th percentile AQI 841999: 90th percentile AQI 842000: 90th percentile AQI 842001: 90th percentile AQI 842002: 90th percentile AQI 932003: 90th percentile AQI 1012004: 90th percentile AQI 712005: 90th percentile AQI 872006: 90th percentile AQI 872007: 90th percentile AQI 802008: 90th percentile AQI 772009: 90th percentile AQI 582010: 90th percentile AQI 642011: 90th percentile AQI 512012: 90th percentile AQI 562013: 90th percentile AQI 502014: 90th percentile AQI 452015: 90th percentile AQI 492016: 90th percentile AQI 472017: 90th percentile AQI 482018: 90th percentile AQI 472019: 90th percentile AQI 452020: 90th percentile AQI 462021: 90th percentile AQI 492022: 90th percentile AQI 462023: 90th percentile AQI 492024: 90th percentile AQI 462025: 90th percentile AQI 461987: Median AQI 401988: Median AQI 461989: Median AQI 441990: Median AQI 401991: Median AQI 431992: Median AQI 411993: Median AQI 411994: Median AQI 441995: Median AQI 411996: Median AQI 431997: Median AQI 411998: Median AQI 401999: Median AQI 412000: Median AQI 362001: Median AQI 392002: Median AQI 412003: Median AQI 432004: Median AQI 412005: Median AQI 432006: Median AQI 432007: Median AQI 402008: Median AQI 432009: Median AQI 342010: Median AQI 402011: Median AQI 362012: Median AQI 372013: Median AQI 362014: Median AQI 352015: Median AQI 342016: Median AQI 362017: Median AQI 372018: Median AQI 362019: Median AQI 362020: Median AQI 362021: Median AQI 362022: Median AQI 362023: Median AQI 372024: Median AQI 362025: Median AQI 36198719921997200220072012201720222025
  • 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
Ozone35798%
Fine particles (PM2.5)72%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253643412030003646129Ozone
20243533331910003646101Ozone
20233583312430003749140Ozone
2022360341190000364693Ozone
20213593312530003649126Ozone
20203513391020003646108Ozone
2019359346130000364593Ozone
20183603352140003647133Ozone
20173583322150003748150Ozone
20163623342710003647115Ozone
20153172892440003449122Ozone
2014363347160000354584Ozone
20133152882340003650129Ozone
20122582232861003756156Ozone
20112752462630003651112Ozone
20102672213961004064151Ozone
20092371983540003458140Ozone
20082391795261104377201Ozone
200723317047151004080169Ozone
200624317353142104387201Ozone
200523315956117004387174Ozone
20042411864491104171202Ozone
2003231162451671043101205Ozone
200229822746168104193207Ozone
2001365293461310303984220Ozone
200027522041112103684222Ozone
1999272217321110204184212Ozone
199836428360191104084205Ozone
19972171582815142041126205Ozone
1996212147461162043100205Ozone
1995213157321653041108221Ozone
199421014845134004493177Ozone
199319514831124004193177Ozone
1992213157371342041100205Ozone
19911981333118106043140232Ozone
199020915436117104097210Ozone
1989193120442162044122212Ozone
198820412035251212046164252Ozone
19871781283865104090203Ozone

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 Massachusetts with a similar median AQI in 2025

All monitored counties in Massachusetts

Source: U.S. EPA AirData, “Annual AQI by County” files for 1987–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem