EnviroNearby

Chittenden County, Vermont air quality history

Daily Air Quality Index summaries from EPA monitors in Chittenden, Vermont, 1980–2025.

88%
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 Chittenden, Vermont on 365 days. 320 of those days (88%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in Vermont (median 37 across 3 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 293 days. Across the years with fuller monitoring, the share of Good days fell: an average of 91% 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 325 of 356 days1980: Moderate 24 of 356 days1980: Unhealthy for Sensitive Groups 5 of 356 days1980: Unhealthy 2 of 356 days19801981: Good 324 of 348 days1981: Moderate 21 of 348 days1981: Unhealthy for Sensitive Groups 3 of 348 days1982: Good 315 of 354 days1982: Moderate 27 of 354 days1982: Unhealthy for Sensitive Groups 11 of 354 days1982: Unhealthy 1 of 354 days1983: Good 312 of 352 days1983: Moderate 31 of 352 days1983: Unhealthy for Sensitive Groups 8 of 352 days1983: Unhealthy 1 of 352 days1984: Good 290 of 318 days1984: Moderate 23 of 318 days1984: Unhealthy for Sensitive Groups 4 of 318 days1984: Unhealthy 1 of 318 days1985: Good 331 of 361 days1985: Moderate 24 of 361 days1985: Unhealthy for Sensitive Groups 5 of 361 days1985: Unhealthy 1 of 361 days19851986: Good 327 of 365 days1986: Moderate 31 of 365 days1986: Unhealthy for Sensitive Groups 7 of 365 days1987: Good 314 of 365 days1987: Moderate 46 of 365 days1987: Unhealthy for Sensitive Groups 5 of 365 days1988: Good 309 of 366 days1988: Moderate 41 of 366 days1988: Unhealthy for Sensitive Groups 14 of 366 days1988: Unhealthy 2 of 366 days1989: Good 300 of 365 days1989: Moderate 62 of 365 days1989: Unhealthy for Sensitive Groups 3 of 365 days1990: Good 321 of 365 days1990: Moderate 37 of 365 days1990: Unhealthy for Sensitive Groups 7 of 365 days19901991: Good 313 of 365 days1991: Moderate 38 of 365 days1991: Unhealthy for Sensitive Groups 14 of 365 days1992: Good 328 of 366 days1992: Moderate 30 of 366 days1992: Unhealthy for Sensitive Groups 4 of 366 days1992: Unhealthy 4 of 366 days1993: Good 313 of 365 days1993: Moderate 43 of 365 days1993: Unhealthy for Sensitive Groups 7 of 365 days1993: Unhealthy 2 of 365 days1994: Good 279 of 365 days1994: Moderate 78 of 365 days1994: Unhealthy for Sensitive Groups 8 of 365 days1995: Good 310 of 365 days1995: Moderate 47 of 365 days1995: Unhealthy for Sensitive Groups 8 of 365 days19951996: Good 322 of 365 days1996: Moderate 42 of 365 days1996: Unhealthy 1 of 365 days1997: Good 330 of 362 days1997: Moderate 28 of 362 days1997: Unhealthy for Sensitive Groups 4 of 362 days1998: Good 308 of 365 days1998: Moderate 50 of 365 days1998: Unhealthy for Sensitive Groups 7 of 365 days1999: Good 284 of 362 days1999: Moderate 69 of 362 days1999: Unhealthy for Sensitive Groups 8 of 362 days1999: Unhealthy 1 of 362 days2000: Good 256 of 316 days2000: Moderate 56 of 316 days2000: Unhealthy for Sensitive Groups 4 of 316 days20002001: Good 212 of 303 days2001: Moderate 84 of 303 days2001: Unhealthy for Sensitive Groups 7 of 303 days2002: Good 282 of 363 days2002: Moderate 69 of 363 days2002: Unhealthy for Sensitive Groups 9 of 363 days2002: Unhealthy 3 of 363 days2003: Good 277 of 365 days2003: Moderate 82 of 365 days2003: Unhealthy for Sensitive Groups 6 of 365 days2004: Good 292 of 366 days2004: Moderate 69 of 366 days2004: Unhealthy for Sensitive Groups 5 of 366 days2005: Good 277 of 365 days2005: Moderate 83 of 365 days2005: Unhealthy for Sensitive Groups 5 of 365 days20052006: Good 307 of 365 days2006: Moderate 56 of 365 days2006: Unhealthy for Sensitive Groups 2 of 365 days2007: Good 298 of 365 days2007: Moderate 61 of 365 days2007: Unhealthy for Sensitive Groups 5 of 365 days2007: Unhealthy 1 of 365 days2008: Good 248 of 366 days2008: Moderate 112 of 366 days2008: Unhealthy for Sensitive Groups 6 of 366 days2009: Good 245 of 365 days2009: Moderate 120 of 365 days2010: Good 259 of 365 days2010: Moderate 104 of 365 days2010: Unhealthy for Sensitive Groups 1 of 365 days2010: Unhealthy 1 of 365 days20102011: Good 250 of 365 days2011: Moderate 113 of 365 days2011: Unhealthy for Sensitive Groups 2 of 365 days2012: Good 307 of 366 days2012: Moderate 59 of 366 days2013: Good 260 of 365 days2013: Moderate 104 of 365 days2013: Unhealthy for Sensitive Groups 1 of 365 days2014: Good 288 of 365 days2014: Moderate 77 of 365 days2015: Good 278 of 365 days2015: Moderate 87 of 365 days20152016: Good 319 of 366 days2016: Moderate 47 of 366 days2017: Good 312 of 365 days2017: Moderate 53 of 365 days2018: Good 295 of 365 days2018: Moderate 70 of 365 days2019: Good 306 of 365 days2019: Moderate 59 of 365 days2020: Good 302 of 366 days2020: Moderate 64 of 366 days20202021: Good 288 of 365 days2021: Moderate 76 of 365 days2021: Unhealthy for Sensitive Groups 1 of 365 days2022: Good 298 of 365 days2022: Moderate 67 of 365 days2023: Good 259 of 365 days2023: Moderate 100 of 365 days2023: Unhealthy for Sensitive Groups 4 of 365 days2023: Unhealthy 2 of 365 days2024: Good 323 of 366 days2024: Moderate 43 of 366 days2025: Good 320 of 365 days2025: Moderate 41 of 365 days2025: Unhealthy for Sensitive Groups 3 of 365 days2025: Unhealthy 1 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 year0501001980: 90th percentile AQI 471981: 90th percentile AQI 471982: 90th percentile AQI 541983: 90th percentile AQI 511984: 90th percentile AQI 491985: 90th percentile AQI 481986: 90th percentile AQI 511987: 90th percentile AQI 561988: 90th percentile AQI 711989: 90th percentile AQI 611990: 90th percentile AQI 541991: 90th percentile AQI 631992: 90th percentile AQI 511993: 90th percentile AQI 601994: 90th percentile AQI 671995: 90th percentile AQI 641996: 90th percentile AQI 511997: 90th percentile AQI 501998: 90th percentile AQI 611999: 90th percentile AQI 672000: 90th percentile AQI 592001: 90th percentile AQI 672002: 90th percentile AQI 652003: 90th percentile AQI 622004: 90th percentile AQI 612005: 90th percentile AQI 632006: 90th percentile AQI 582007: 90th percentile AQI 612008: 90th percentile AQI 662009: 90th percentile AQI 612010: 90th percentile AQI 642011: 90th percentile AQI 602012: 90th percentile AQI 562013: 90th percentile AQI 602014: 90th percentile AQI 582015: 90th percentile AQI 592016: 90th percentile AQI 522017: 90th percentile AQI 522018: 90th percentile AQI 562019: 90th percentile AQI 542020: 90th percentile AQI 532021: 90th percentile AQI 572022: 90th percentile AQI 532023: 90th percentile AQI 592024: 90th percentile AQI 512025: 90th percentile AQI 551980: Median AQI 201981: Median AQI 231982: Median AQI 251983: Median AQI 271984: Median AQI 311985: Median AQI 311986: Median AQI 341987: Median AQI 361988: Median AQI 341989: Median AQI 361990: Median AQI 341991: Median AQI 341992: Median AQI 331993: Median AQI 331994: Median AQI 371995: Median AQI 351996: Median AQI 341997: Median AQI 341998: Median AQI 351999: Median AQI 382000: Median AQI 362001: Median AQI 412002: Median AQI 382003: Median AQI 382004: Median AQI 372005: Median AQI 412006: Median AQI 362007: Median AQI 352008: Median AQI 422009: Median AQI 412010: Median AQI 412011: Median AQI 432012: Median AQI 372013: Median AQI 422014: Median AQI 412015: Median AQI 392016: Median AQI 362017: Median AQI 372018: Median AQI 402019: Median AQI 392020: Median AQI 392021: Median AQI 402022: Median AQI 412023: Median AQI 422024: 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
Ozone29380%
Fine particles (PM2.5)7220%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253653204131003855156Ozone
2024366323430000375184Ozone
202336525910042004259160Ozone
2022365298670000415390Ozone
20213652887610004057129PM2.5
2020366302640000395398Ozone
2019365306590000395482Ozone
2018365295700000405690Ozone
2017365312530000375274Ozone
2016366319470000365280Ozone
20153652788700003959100Ozone
2014365288770000415885Ozone
201336526010410004260133Ozone
20123663075900003756100Ozone
201136525011320004360105PM2.5
201036525910411004164162PM2.5
20093652451200000416193PM2.5
200836624811260004266143PM2.5
20073652986151003561151Ozone
20063653075620003658122Ozone
20053652778350004163143Ozone
20043662926950003761129Ozone
20033652778260003862122Ozone
20023632826993003865177Ozone
20013032128470004167140Ozone
20003162565640003659133Ozone
19993622846981003867156Ozone
19983653085070003561140Ozone
19973623302840003450115NO2
19963653224201003451161Ozone
19953653104780003564133Ozone
19943652797880003767122Ozone
19933653134372003360159Ozone
19923663283044003351164Ozone
199136531338140003463150Ozone
19903653213770003454122NO2
19893653006230003661150Ozone
198836630941142003471185NO2
19873653144650003656136NO2
19863653273170003451140Ozone
19853613312451003148151Ozone
19843182902341003149177Ozone
19833523123181002751159Ozone
198235431527111002554169CO
19813483242130002347129CO
19803563252452002047164CO

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 Vermont with a similar median AQI in 2025

All monitored counties in Vermont

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