EnviroNearby

Bristol County, Massachusetts air quality history

Daily Air Quality Index summaries from EPA monitors in Bristol, Massachusetts, 1980–2025.

84%
Good days in 2025
38
Median daily AQI, 2025
3
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 Bristol, Massachusetts on 365 days. 306 of those days (84%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in Massachusetts (median 38 across 13 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 295 days. Across the years with fuller monitoring, the share of Good days rose: an average of 68% in 1980–1982 versus 82% 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 140 of 202 days1980: Moderate 32 of 202 days1980: Unhealthy for Sensitive Groups 16 of 202 days1980: Unhealthy 11 of 202 days1980: Very Unhealthy 3 of 202 days19801981: Good 141 of 209 days1981: Moderate 36 of 209 days1981: Unhealthy for Sensitive Groups 18 of 209 days1981: Unhealthy 12 of 209 days1981: Very Unhealthy 2 of 209 days1982: Good 137 of 208 days1982: Moderate 38 of 208 days1982: Unhealthy for Sensitive Groups 22 of 208 days1982: Unhealthy 9 of 208 days1982: Very Unhealthy 2 of 208 days1983: Good 210 of 323 days1983: Moderate 47 of 323 days1983: Unhealthy for Sensitive Groups 28 of 323 days1983: Unhealthy 22 of 323 days1983: Very Unhealthy 16 of 323 days1984: Good 243 of 349 days1984: Moderate 53 of 349 days1984: Unhealthy for Sensitive Groups 23 of 349 days1984: Unhealthy 22 of 349 days1984: Very Unhealthy 8 of 349 days1985: Good 224 of 322 days1985: Moderate 52 of 322 days1985: Unhealthy for Sensitive Groups 25 of 322 days1985: Unhealthy 15 of 322 days1985: Very Unhealthy 6 of 322 days19851986: Good 148 of 218 days1986: Moderate 41 of 218 days1986: Unhealthy for Sensitive Groups 17 of 218 days1986: Unhealthy 8 of 218 days1986: Very Unhealthy 4 of 218 days1987: Good 144 of 213 days1987: Moderate 38 of 213 days1987: Unhealthy for Sensitive Groups 18 of 213 days1987: Unhealthy 11 of 213 days1987: Very Unhealthy 2 of 213 days1988: Good 136 of 215 days1988: Moderate 34 of 215 days1988: Unhealthy for Sensitive Groups 25 of 215 days1988: Unhealthy 12 of 215 days1988: Very Unhealthy 8 of 215 days1989: Good 151 of 239 days1989: Moderate 62 of 239 days1989: Unhealthy for Sensitive Groups 15 of 239 days1989: Unhealthy 8 of 239 days1989: Very Unhealthy 3 of 239 days1990: Good 170 of 240 days1990: Moderate 40 of 240 days1990: Unhealthy for Sensitive Groups 18 of 240 days1990: Unhealthy 9 of 240 days1990: Very Unhealthy 3 of 240 days19901991: Good 171 of 238 days1991: Moderate 32 of 238 days1991: Unhealthy for Sensitive Groups 20 of 238 days1991: Unhealthy 10 of 238 days1991: Very Unhealthy 5 of 238 days1992: Good 170 of 241 days1992: Moderate 48 of 241 days1992: Unhealthy for Sensitive Groups 15 of 241 days1992: Unhealthy 8 of 241 days1993: Good 185 of 239 days1993: Moderate 36 of 239 days1993: Unhealthy for Sensitive Groups 11 of 239 days1993: Unhealthy 7 of 239 days1994: Good 173 of 241 days1994: Moderate 48 of 241 days1994: Unhealthy for Sensitive Groups 12 of 241 days1994: Unhealthy 8 of 241 days1995: Good 212 of 282 days1995: Moderate 37 of 282 days1995: Unhealthy for Sensitive Groups 22 of 282 days1995: Unhealthy 4 of 282 days1995: Very Unhealthy 7 of 282 days19951996: Good 286 of 364 days1996: Moderate 55 of 364 days1996: Unhealthy for Sensitive Groups 16 of 364 days1996: Unhealthy 6 of 364 days1996: Very Unhealthy 1 of 364 days1997: Good 290 of 365 days1997: Moderate 43 of 365 days1997: Unhealthy for Sensitive Groups 18 of 365 days1997: Unhealthy 12 of 365 days1997: Very Unhealthy 2 of 365 days1998: Good 278 of 365 days1998: Moderate 59 of 365 days1998: Unhealthy for Sensitive Groups 20 of 365 days1998: Unhealthy 8 of 365 days1999: Good 182 of 304 days1999: Moderate 95 of 304 days1999: Unhealthy for Sensitive Groups 18 of 304 days1999: Unhealthy 7 of 304 days1999: Very Unhealthy 2 of 304 days2000: Good 164 of 283 days2000: Moderate 102 of 283 days2000: Unhealthy for Sensitive Groups 15 of 283 days2000: Unhealthy 2 of 283 days20002001: Good 160 of 291 days2001: Moderate 95 of 291 days2001: Unhealthy for Sensitive Groups 20 of 291 days2001: Unhealthy 12 of 291 days2001: Very Unhealthy 4 of 291 days2002: Good 132 of 235 days2002: Moderate 81 of 235 days2002: Unhealthy for Sensitive Groups 16 of 235 days2002: Unhealthy 6 of 235 days2003: Good 174 of 289 days2003: Moderate 95 of 289 days2003: Unhealthy for Sensitive Groups 13 of 289 days2003: Unhealthy 6 of 289 days2003: Very Unhealthy 1 of 289 days2004: Good 160 of 366 days2004: Moderate 190 of 366 days2004: Unhealthy for Sensitive Groups 15 of 366 days2004: Unhealthy 1 of 366 days2005: Good 180 of 359 days2005: Moderate 165 of 359 days2005: Unhealthy for Sensitive Groups 13 of 359 days2005: Unhealthy 1 of 359 days20052006: Good 209 of 363 days2006: Moderate 139 of 363 days2006: Unhealthy for Sensitive Groups 12 of 363 days2006: Unhealthy 2 of 363 days2006: Very Unhealthy 1 of 363 days2007: Good 202 of 346 days2007: Moderate 132 of 346 days2007: Unhealthy for Sensitive Groups 11 of 346 days2007: Unhealthy 1 of 346 days2008: Good 227 of 366 days2008: Moderate 130 of 366 days2008: Unhealthy for Sensitive Groups 8 of 366 days2008: Unhealthy 1 of 366 days2009: Good 242 of 357 days2009: Moderate 112 of 357 days2009: Unhealthy for Sensitive Groups 3 of 357 days2010: Good 230 of 365 days2010: Moderate 129 of 365 days2010: Unhealthy for Sensitive Groups 6 of 365 days20102011: Good 165 of 364 days2011: Moderate 194 of 364 days2011: Unhealthy for Sensitive Groups 5 of 364 days2012: Good 240 of 353 days2012: Moderate 106 of 353 days2012: Unhealthy for Sensitive Groups 6 of 353 days2012: Unhealthy 1 of 353 days2013: Good 220 of 359 days2013: Moderate 132 of 359 days2013: Unhealthy for Sensitive Groups 6 of 359 days2013: Unhealthy 1 of 359 days2014: Good 243 of 365 days2014: Moderate 122 of 365 days2015: Good 260 of 365 days2015: Moderate 100 of 365 days2015: Unhealthy for Sensitive Groups 5 of 365 days20152016: Good 307 of 366 days2016: Moderate 55 of 366 days2016: Unhealthy for Sensitive Groups 4 of 366 days2017: Good 260 of 365 days2017: Moderate 99 of 365 days2017: Unhealthy for Sensitive Groups 5 of 365 days2017: Unhealthy 1 of 365 days2018: Good 258 of 365 days2018: Moderate 97 of 365 days2018: Unhealthy for Sensitive Groups 10 of 365 days2019: Good 279 of 364 days2019: Moderate 85 of 364 days2020: Good 250 of 366 days2020: Moderate 113 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days20202021: Good 279 of 365 days2021: Moderate 84 of 365 days2021: Unhealthy for Sensitive Groups 2 of 365 days2022: Good 301 of 365 days2022: Moderate 63 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days2023: Good 269 of 365 days2023: Moderate 87 of 365 days2023: Unhealthy for Sensitive Groups 9 of 365 days2024: Good 322 of 366 days2024: Moderate 42 of 366 days2024: Unhealthy for Sensitive Groups 2 of 366 days2025: Good 306 of 365 days2025: Moderate 56 of 365 days2025: Unhealthy for Sensitive Groups 3 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 year0501001502001980: 90th percentile AQI 1261981: 90th percentile AQI 1291982: 90th percentile AQI 1191983: 90th percentile AQI 1691984: 90th percentile AQI 1401985: 90th percentile AQI 1191986: 90th percentile AQI 1191987: 90th percentile AQI 1151988: 90th percentile AQI 1501989: 90th percentile AQI 1051990: 90th percentile AQI 1121991: 90th percentile AQI 1261992: 90th percentile AQI 971993: 90th percentile AQI 901994: 90th percentile AQI 971995: 90th percentile AQI 1081996: 90th percentile AQI 871997: 90th percentile AQI 971998: 90th percentile AQI 871999: 90th percentile AQI 972000: 90th percentile AQI 842001: 90th percentile AQI 1152002: 90th percentile AQI 972003: 90th percentile AQI 902004: 90th percentile AQI 782005: 90th percentile AQI 752006: 90th percentile AQI 792007: 90th percentile AQI 782008: 90th percentile AQI 742009: 90th percentile AQI 662010: 90th percentile AQI 682011: 90th percentile AQI 712012: 90th percentile AQI 612013: 90th percentile AQI 642014: 90th percentile AQI 602015: 90th percentile AQI 612016: 90th percentile AQI 552017: 90th percentile AQI 612018: 90th percentile AQI 592019: 90th percentile AQI 562020: 90th percentile AQI 582021: 90th percentile AQI 562022: 90th percentile AQI 542023: 90th percentile AQI 612024: 90th percentile AQI 532025: 90th percentile AQI 561980: Median AQI 431981: Median AQI 431982: Median AQI 421983: Median AQI 381984: Median AQI 411985: Median AQI 411986: Median AQI 431987: Median AQI 431988: Median AQI 441989: Median AQI 441990: Median AQI 401991: Median AQI 411992: Median AQI 411993: Median AQI 381994: Median AQI 421995: Median AQI 391996: Median AQI 381997: Median AQI 381998: Median AQI 381999: Median AQI 472000: Median AQI 442001: Median AQI 472002: Median AQI 472003: Median AQI 462004: Median AQI 522005: Median AQI 502006: Median AQI 452007: Median AQI 442008: Median AQI 442009: Median AQI 392010: Median AQI 442011: Median AQI 522012: Median AQI 432013: Median AQI 442014: Median AQI 432015: Median AQI 392016: Median AQI 372017: Median AQI 422018: Median AQI 442019: Median AQI 432020: Median AQI 422021: Median AQI 392022: Median AQI 382023: Median AQI 422024: Median AQI 382025: 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
Ozone29581%
Fine particles (PM2.5)7019%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253653065630003856119Ozone
20243663224220003853108Ozone
20233652698790004261137Ozone
20223653016310003854115Ozone
20213652798420003956147Ozone
202036625011330004258119Ozone
2019364279850000435697Ozone
201836525897100004459133Ozone
20173652609951004261151Ozone
20163663075540003755133Ozone
201536526010050003961122Ozone
20143652431220000436084PM2.5
201335922013261004464161PM2.5
201235324010661004361161PM2.5
201136416519450005271150PM2.5
201036523012960004468136PM2.5
200935724211230003966126PM2.5
200836622713081004474156PM2.5
2007346202132111004478151PM2.5
2006363209139122104579202PM2.5
2005359180165131005075151PM2.5
2004366160190151005278185PM2.5
200328917495136104690213Ozone
200223513281166004797200Ozone
20012911609520124047115213Ozone
2000283164102152004484200Ozone
199930418295187204797207Ozone
199836527859208003887200Ozone
1997365290431812203897202Ozone
199636428655166103887208Ozone
1995282212372247039108221Ozone
199424117348128004297195Ozone
199323918536117003890187Ozone
199224117048158004197195Ozone
19912381713220105041126216Ozone
1990240170401893040112206Ozone
1989239151621583044105214Ozone
19882151363425128044150234Ozone
19872131443818112043115203Ozone
1986218148411784043119209Ozone
19853222245225156041119218Ozone
19843492435323228041140246NO2
198332321047282216038169240Ozone
1982208137382292042119221Ozone
19812091413618122043129206Ozone
19802021403216113043126220Ozone

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 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