EnviroNearby

Tolland County, Connecticut air quality history

Daily Air Quality Index summaries from EPA monitors in Tolland, Connecticut, 1980–2025.

84%
Good days in 2025
40
Median daily AQI, 2025
5
Days above 100 in 2025
209
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Tolland, Connecticut on 209 days. 175 of those days (84%) were in the Good range, and the median daily AQI was 40. That median is about the same as the typical monitored county in Connecticut (median 41 across 8 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 209 days. Across the years with fuller monitoring, the share of Good days rose: an average of 49% in 1980–1982 versus 86% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (209 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

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 72 of 148 days1980: Moderate 27 of 148 days1980: Unhealthy for Sensitive Groups 24 of 148 days1980: Unhealthy 14 of 148 days1980: Very Unhealthy 11 of 148 days19801981: Good 91 of 164 days1981: Moderate 43 of 164 days1981: Unhealthy for Sensitive Groups 12 of 164 days1981: Unhealthy 13 of 164 days1981: Very Unhealthy 5 of 164 days1982: Good 72 of 164 days1982: Moderate 37 of 164 days1982: Unhealthy for Sensitive Groups 28 of 164 days1982: Unhealthy 20 of 164 days1982: Very Unhealthy 7 of 164 days1983: Good 100 of 213 days1983: Moderate 44 of 213 days1983: Unhealthy for Sensitive Groups 31 of 213 days1983: Unhealthy 21 of 213 days1983: Very Unhealthy 17 of 213 days1984: Good 106 of 178 days1984: Moderate 35 of 178 days1984: Unhealthy for Sensitive Groups 20 of 178 days1984: Unhealthy 11 of 178 days1984: Very Unhealthy 6 of 178 days1985: Good 130 of 210 days1985: Moderate 44 of 210 days1985: Unhealthy for Sensitive Groups 23 of 210 days1985: Unhealthy 11 of 210 days1985: Very Unhealthy 2 of 210 days19851986: Good 158 of 206 days1986: Moderate 32 of 206 days1986: Unhealthy for Sensitive Groups 12 of 206 days1986: Unhealthy 3 of 206 days1986: Very Unhealthy 1 of 206 days1987: Good 151 of 208 days1987: Moderate 33 of 208 days1987: Unhealthy for Sensitive Groups 19 of 208 days1987: Unhealthy 5 of 208 days1988: Good 143 of 212 days1988: Moderate 27 of 212 days1988: Unhealthy for Sensitive Groups 16 of 212 days1988: Unhealthy 16 of 212 days1988: Very Unhealthy 10 of 212 days1989: Good 110 of 182 days1989: Moderate 49 of 182 days1989: Unhealthy for Sensitive Groups 15 of 182 days1989: Unhealthy 6 of 182 days1989: Very Unhealthy 2 of 182 days1990: Good 141 of 207 days1990: Moderate 42 of 207 days1990: Unhealthy for Sensitive Groups 13 of 207 days1990: Unhealthy 7 of 207 days1990: Very Unhealthy 4 of 207 days19901991: Good 162 of 213 days1991: Moderate 26 of 213 days1991: Unhealthy for Sensitive Groups 18 of 213 days1991: Unhealthy 5 of 213 days1991: Very Unhealthy 2 of 213 days1992: Good 158 of 213 days1992: Moderate 31 of 213 days1992: Unhealthy for Sensitive Groups 14 of 213 days1992: Unhealthy 8 of 213 days1992: Very Unhealthy 2 of 213 days1993: Good 154 of 213 days1993: Moderate 33 of 213 days1993: Unhealthy for Sensitive Groups 16 of 213 days1993: Unhealthy 8 of 213 days1993: Very Unhealthy 2 of 213 days1994: Good 190 of 260 days1994: Moderate 43 of 260 days1994: Unhealthy for Sensitive Groups 14 of 260 days1994: Unhealthy 12 of 260 days1994: Very Unhealthy 1 of 260 days1995: Good 219 of 276 days1995: Moderate 37 of 276 days1995: Unhealthy for Sensitive Groups 14 of 276 days1995: Unhealthy 4 of 276 days1995: Very Unhealthy 2 of 276 days19951996: Good 126 of 181 days1996: Moderate 40 of 181 days1996: Unhealthy for Sensitive Groups 14 of 181 days1996: Unhealthy 1 of 181 days1997: Good 121 of 183 days1997: Moderate 39 of 183 days1997: Unhealthy for Sensitive Groups 13 of 183 days1997: Unhealthy 8 of 183 days1997: Very Unhealthy 2 of 183 days1998: Good 139 of 214 days1998: Moderate 48 of 214 days1998: Unhealthy for Sensitive Groups 20 of 214 days1998: Unhealthy 5 of 214 days1998: Very Unhealthy 2 of 214 days1999: Good 124 of 194 days1999: Moderate 46 of 194 days1999: Unhealthy for Sensitive Groups 13 of 194 days1999: Unhealthy 11 of 194 days2000: Good 149 of 192 days2000: Moderate 29 of 192 days2000: Unhealthy for Sensitive Groups 13 of 192 days2000: Unhealthy 1 of 192 days20002001: Good 115 of 179 days2001: Moderate 41 of 179 days2001: Unhealthy for Sensitive Groups 14 of 179 days2001: Unhealthy 6 of 179 days2001: Very Unhealthy 3 of 179 days2002: Good 109 of 182 days2002: Moderate 42 of 182 days2002: Unhealthy for Sensitive Groups 18 of 182 days2002: Unhealthy 10 of 182 days2002: Very Unhealthy 3 of 182 days2003: Good 133 of 183 days2003: Moderate 41 of 183 days2003: Unhealthy for Sensitive Groups 9 of 183 days2004: Good 141 of 178 days2004: Moderate 27 of 178 days2004: Unhealthy for Sensitive Groups 9 of 178 days2004: Unhealthy 1 of 178 days2005: Good 122 of 180 days2005: Moderate 39 of 180 days2005: Unhealthy for Sensitive Groups 11 of 180 days2005: Unhealthy 7 of 180 days2005: Very Unhealthy 1 of 180 days20052006: Good 127 of 176 days2006: Moderate 34 of 176 days2006: Unhealthy for Sensitive Groups 11 of 176 days2006: Unhealthy 4 of 176 days2007: Good 125 of 172 days2007: Moderate 25 of 172 days2007: Unhealthy for Sensitive Groups 15 of 172 days2007: Unhealthy 6 of 172 days2007: Very Unhealthy 1 of 172 days2008: Good 136 of 183 days2008: Moderate 34 of 183 days2008: Unhealthy for Sensitive Groups 10 of 183 days2008: Unhealthy 3 of 183 days2009: Good 156 of 183 days2009: Moderate 21 of 183 days2009: Unhealthy for Sensitive Groups 6 of 183 days2010: Good 129 of 181 days2010: Moderate 37 of 181 days2010: Unhealthy for Sensitive Groups 13 of 181 days2010: Unhealthy 2 of 181 days20102011: Good 145 of 167 days2011: Moderate 19 of 167 days2011: Unhealthy for Sensitive Groups 2 of 167 days2011: Unhealthy 1 of 167 days2012: Good 125 of 181 days2012: Moderate 37 of 181 days2012: Unhealthy for Sensitive Groups 17 of 181 days2012: Unhealthy 2 of 181 days2013: Good 134 of 172 days2013: Moderate 31 of 172 days2013: Unhealthy for Sensitive Groups 7 of 172 days2014: Good 141 of 178 days2014: Moderate 28 of 178 days2014: Unhealthy for Sensitive Groups 9 of 178 days2015: Good 154 of 183 days2015: Moderate 23 of 183 days2015: Unhealthy for Sensitive Groups 6 of 183 days20152016: Good 144 of 176 days2016: Moderate 27 of 176 days2016: Unhealthy for Sensitive Groups 5 of 176 days2017: Good 188 of 211 days2017: Moderate 20 of 211 days2017: Unhealthy for Sensitive Groups 3 of 211 days2018: Good 189 of 213 days2018: Moderate 20 of 213 days2018: Unhealthy for Sensitive Groups 4 of 213 days2019: Good 187 of 212 days2019: Moderate 20 of 212 days2019: Unhealthy for Sensitive Groups 5 of 212 days2020: Good 192 of 206 days2020: Moderate 14 of 206 days20202021: Good 170 of 201 days2021: Moderate 30 of 201 days2021: Unhealthy for Sensitive Groups 1 of 201 days2022: Good 187 of 208 days2022: Moderate 19 of 208 days2022: Unhealthy for Sensitive Groups 2 of 208 days2023: Good 178 of 212 days2023: Moderate 31 of 212 days2023: Unhealthy for Sensitive Groups 2 of 212 days2023: Unhealthy 1 of 212 days2024: Good 184 of 205 days2024: Moderate 16 of 205 days2024: Unhealthy for Sensitive Groups 4 of 205 days2024: Unhealthy 1 of 205 days2025: Good 175 of 209 days2025: Moderate 29 of 209 days2025: Unhealthy for Sensitive Groups 5 of 209 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 1821981: 90th percentile AQI 1591982: 90th percentile AQI 1611983: 90th percentile AQI 1791984: 90th percentile AQI 1501985: 90th percentile AQI 1291986: 90th percentile AQI 1001987: 90th percentile AQI 1011988: 90th percentile AQI 1661989: 90th percentile AQI 1121990: 90th percentile AQI 1151991: 90th percentile AQI 1081992: 90th percentile AQI 1011993: 90th percentile AQI 1121994: 90th percentile AQI 1011995: 90th percentile AQI 871996: 90th percentile AQI 971997: 90th percentile AQI 1121998: 90th percentile AQI 1151999: 90th percentile AQI 1192000: 90th percentile AQI 842001: 90th percentile AQI 1192002: 90th percentile AQI 1362003: 90th percentile AQI 842004: 90th percentile AQI 772005: 90th percentile AQI 1052006: 90th percentile AQI 972007: 90th percentile AQI 1192008: 90th percentile AQI 842009: 90th percentile AQI 582010: 90th percentile AQI 842011: 90th percentile AQI 582012: 90th percentile AQI 1012013: 90th percentile AQI 712014: 90th percentile AQI 742015: 90th percentile AQI 672016: 90th percentile AQI 712017: 90th percentile AQI 542018: 90th percentile AQI 542019: 90th percentile AQI 542020: 90th percentile AQI 482021: 90th percentile AQI 582022: 90th percentile AQI 512023: 90th percentile AQI 582024: 90th percentile AQI 512025: 90th percentile AQI 611980: Median AQI 541981: Median AQI 481982: Median AQI 611983: Median AQI 541984: Median AQI 461985: Median AQI 441986: Median AQI 391987: Median AQI 401988: Median AQI 421989: Median AQI 461990: Median AQI 441991: Median AQI 411992: Median AQI 391993: Median AQI 411994: Median AQI 421995: Median AQI 361996: Median AQI 431997: Median AQI 451998: Median AQI 461999: Median AQI 452000: Median AQI 392001: Median AQI 462002: Median AQI 472003: Median AQI 432004: Median AQI 402005: Median AQI 442006: Median AQI 442007: Median AQI 412008: Median AQI 412009: Median AQI 382010: Median AQI 432011: Median AQI 392012: Median AQI 442013: Median AQI 412014: Median AQI 412015: Median AQI 392016: Median AQI 412017: Median AQI 392018: Median AQI 382019: Median AQI 422020: Median AQI 392021: Median AQI 392022: Median AQI 392023: Median AQI 412024: Median AQI 372025: Median AQI 401980198519901995200020052010201520202025
  • 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
Ozone209100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20252091752950004061136Ozone
20242051841641003751156Ozone
20232121783121004158156Ozone
20222081871920003951122Ozone
20212011703010003958101Ozone
2020206192140000394893Ozone
20192121872050004254126Ozone
20182131892040003854140Ozone
20172111882030003954147Ozone
20161761442750004171140Ozone
20151831542360003967129Ozone
20141781412890004174140Ozone
20131721343170004171147Ozone
2012181125371720044101177Ozone
20111671451921003958154Ozone
201018112937132004384190Ozone
20091831562160003858140Ozone
200818313634103004184172Ozone
2007172125251561041119202Ozone
200617612734114004497200Ozone
2005180122391171044105201Ozone
20041781412791004077159Ozone
20031831334190004384150Ozone
20021821094218103047136212Ozone
2001179115411463046119218Ozone
200019214929131003984182Ozone
19991941244613110045119190Ozone
1998214139482052046115214Ozone
1997183121391382045112239Ozone
199618112640141004397187Ozone
199527621937144203687209Ozone
19942601904314121042101204Ozone
1993213154331682041112218Ozone
1992213158311482039101212Ozone
1991213162261852041108225Ozone
1990207141421374044115217Ozone
1989182110491562046112219Ozone
198821214327161610042166274Ozone
1987208151331950040101192Ozone
1986206158321231039100217Ozone
19852101304423112044129225Ozone
19841781063520116046150220Ozone
198321310044312117054179239Ozone
1982164723728207061161254Ozone
1981164914312135048159218Ozone
19801487227241411054182223Ozone

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 Connecticut with a similar median AQI in 2025

All monitored counties in Connecticut

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