EnviroNearby

Litchfield County, Connecticut air quality history

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

81%
Good days in 2025
39
Median daily AQI, 2025
9
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 Litchfield, Connecticut on 365 days. 297 of those days (81%) were in the Good range, and the median daily AQI was 39. 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 301 days. Across the years with fuller monitoring, the share of Good days rose: an average of 73% in 1980–1992 versus 81% in 2023–2025.

Years with fewer than 120 monitored days (1988, 1989, 1990, 2001) are shown in the table but left out of comparisons and trend statements.

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 95 of 164 days1980: Moderate 26 of 164 days1980: Unhealthy for Sensitive Groups 17 of 164 days1980: Unhealthy 14 of 164 days1980: Very Unhealthy 12 of 164 days19801988: Good 29 of 29 days1989: Good 61 of 61 days1990: Good 60 of 61 days1990: Moderate 1 of 61 days1991: Good 178 of 236 days1991: Moderate 38 of 236 days1991: Unhealthy for Sensitive Groups 9 of 236 days1991: Unhealthy 10 of 236 days1991: Very Unhealthy 1 of 236 days1992: Good 206 of 240 days1992: Moderate 24 of 240 days1992: Unhealthy for Sensitive Groups 8 of 240 days1992: Unhealthy 2 of 240 days19921993: Good 181 of 237 days1993: Moderate 37 of 237 days1993: Unhealthy for Sensitive Groups 11 of 237 days1993: Unhealthy 7 of 237 days1993: Very Unhealthy 1 of 237 days1994: Good 169 of 232 days1994: Moderate 39 of 232 days1994: Unhealthy for Sensitive Groups 19 of 232 days1994: Unhealthy 5 of 232 days1995: Good 181 of 239 days1995: Moderate 36 of 239 days1995: Unhealthy for Sensitive Groups 15 of 239 days1995: Unhealthy 6 of 239 days1995: Very Unhealthy 1 of 239 days1996: Good 147 of 209 days1996: Moderate 46 of 209 days1996: Unhealthy for Sensitive Groups 12 of 209 days1996: Unhealthy 4 of 209 days1997: Good 152 of 209 days1997: Moderate 39 of 209 days1997: Unhealthy for Sensitive Groups 10 of 209 days1997: Unhealthy 8 of 209 days19971998: Good 163 of 240 days1998: Moderate 51 of 240 days1998: Unhealthy for Sensitive Groups 17 of 240 days1998: Unhealthy 9 of 240 days1999: Good 127 of 211 days1999: Moderate 53 of 211 days1999: Unhealthy for Sensitive Groups 19 of 211 days1999: Unhealthy 12 of 211 days2000: Good 176 of 222 days2000: Moderate 33 of 222 days2000: Unhealthy for Sensitive Groups 10 of 222 days2000: Unhealthy 3 of 222 days2001: Good 85 of 103 days2001: Moderate 15 of 103 days2001: Unhealthy for Sensitive Groups 1 of 103 days2001: Unhealthy 2 of 103 days2002: Good 143 of 232 days2002: Moderate 55 of 232 days2002: Unhealthy for Sensitive Groups 22 of 232 days2002: Unhealthy 10 of 232 days2002: Very Unhealthy 2 of 232 days20022003: Good 154 of 243 days2003: Moderate 72 of 243 days2003: Unhealthy for Sensitive Groups 14 of 243 days2003: Unhealthy 3 of 243 days2004: Good 169 of 237 days2004: Moderate 58 of 237 days2004: Unhealthy for Sensitive Groups 8 of 237 days2004: Unhealthy 2 of 237 days2005: Good 212 of 300 days2005: Moderate 64 of 300 days2005: Unhealthy for Sensitive Groups 17 of 300 days2005: Unhealthy 7 of 300 days2006: Good 274 of 361 days2006: Moderate 66 of 361 days2006: Unhealthy for Sensitive Groups 18 of 361 days2006: Unhealthy 3 of 361 days2007: Good 264 of 365 days2007: Moderate 71 of 365 days2007: Unhealthy for Sensitive Groups 23 of 365 days2007: Unhealthy 6 of 365 days2007: Very Unhealthy 1 of 365 days20072008: Good 294 of 366 days2008: Moderate 63 of 366 days2008: Unhealthy for Sensitive Groups 8 of 366 days2008: Unhealthy 1 of 366 days2009: Good 314 of 365 days2009: Moderate 48 of 365 days2009: Unhealthy for Sensitive Groups 3 of 365 days2010: Good 297 of 365 days2010: Moderate 63 of 365 days2010: Unhealthy for Sensitive Groups 4 of 365 days2010: Unhealthy 1 of 365 days2011: Good 312 of 359 days2011: Moderate 44 of 359 days2011: Unhealthy for Sensitive Groups 3 of 359 days2012: Good 234 of 364 days2012: Moderate 124 of 364 days2012: Unhealthy for Sensitive Groups 6 of 364 days20122013: Good 236 of 365 days2013: Moderate 126 of 365 days2013: Unhealthy for Sensitive Groups 3 of 365 days2014: Good 243 of 365 days2014: Moderate 120 of 365 days2014: Unhealthy for Sensitive Groups 2 of 365 days2015: Good 279 of 365 days2015: Moderate 79 of 365 days2015: Unhealthy for Sensitive Groups 7 of 365 days2016: Good 296 of 366 days2016: Moderate 62 of 366 days2016: Unhealthy for Sensitive Groups 7 of 366 days2016: Unhealthy 1 of 366 days2017: Good 317 of 365 days2017: Moderate 46 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days20172018: Good 308 of 363 days2018: Moderate 51 of 363 days2018: Unhealthy for Sensitive Groups 4 of 363 days2019: Good 327 of 365 days2019: Moderate 38 of 365 days2020: Good 300 of 362 days2020: Moderate 62 of 362 days2021: Good 300 of 364 days2021: Moderate 61 of 364 days2021: Unhealthy for Sensitive Groups 3 of 364 days2022: Good 308 of 365 days2022: Moderate 54 of 365 days2022: Unhealthy for Sensitive Groups 3 of 365 days20222023: Good 285 of 364 days2023: Moderate 72 of 364 days2023: Unhealthy for Sensitive Groups 3 of 364 days2023: Unhealthy 4 of 364 days2024: Good 305 of 362 days2024: Moderate 49 of 362 days2024: Unhealthy for Sensitive Groups 8 of 362 days2025: Good 297 of 365 days2025: Moderate 59 of 365 days2025: Unhealthy for Sensitive Groups 8 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 year0501001502001980: 90th percentile AQI 1821988: 90th percentile AQI 391989: 90th percentile AQI 361990: 90th percentile AQI 321991: 90th percentile AQI 931992: 90th percentile AQI 611993: 90th percentile AQI 871994: 90th percentile AQI 1011995: 90th percentile AQI 971996: 90th percentile AQI 931997: 90th percentile AQI 931998: 90th percentile AQI 1051999: 90th percentile AQI 1262000: 90th percentile AQI 842001: 90th percentile AQI 742002: 90th percentile AQI 1262003: 90th percentile AQI 902004: 90th percentile AQI 842005: 90th percentile AQI 872006: 90th percentile AQI 772007: 90th percentile AQI 902008: 90th percentile AQI 622009: 90th percentile AQI 542010: 90th percentile AQI 612011: 90th percentile AQI 532012: 90th percentile AQI 672013: 90th percentile AQI 632014: 90th percentile AQI 612015: 90th percentile AQI 642016: 90th percentile AQI 612017: 90th percentile AQI 542018: 90th percentile AQI 572019: 90th percentile AQI 512020: 90th percentile AQI 542021: 90th percentile AQI 582022: 90th percentile AQI 582023: 90th percentile AQI 592024: 90th percentile AQI 582025: 90th percentile AQI 641980: Median AQI 441988: Median AQI 161989: Median AQI 191990: Median AQI 161991: Median AQI 391992: Median AQI 331993: Median AQI 381994: Median AQI 411995: Median AQI 421996: Median AQI 421997: Median AQI 421998: Median AQI 441999: Median AQI 462000: Median AQI 382001: Median AQI 282002: Median AQI 462003: Median AQI 442004: Median AQI 412005: Median AQI 412006: Median AQI 402007: Median AQI 412008: Median AQI 372009: Median AQI 342010: Median AQI 382011: Median AQI 382012: Median AQI 442013: Median AQI 452014: Median AQI 442015: Median AQI 422016: Median AQI 392017: Median AQI 372018: Median AQI 362019: Median AQI 372020: Median AQI 392021: Median AQI 382022: Median AQI 402023: Median AQI 382024: Median AQI 382025: Median AQI 39198019921997200220072012201720222025
  • 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
Ozone30182%
Fine particles (PM2.5)6418%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652975981003964161Ozone
20243623054980003858119Ozone
20233642857234003859183Ozone
20223653085430004058108Ozone
20213643006130003858142Ozone
2020362300620000395484Ozone
2019365327380000375197Ozone
20183633085140003657133Ozone
20173653174620003754122Ozone
20163662966271003961164Ozone
20153652797970004264147Ozone
201436524312020004461129Ozone
201336523612630004563150Ozone
201236423412460004467129Ozone
20113593124430003853150Ozone
20103652976341003861154Ozone
20093653144830003454112Ozone
20083662946381003762161Ozone
200736526471236104190219Ozone
200636127466183004077187Ozone
200530021264177004187185Ozone
20042371695882004184185Ozone
200324315472143004490182Ozone
20022321435522102046126217Ozone
2001103851512002874182PM10
200022217633103003884179Ozone
19992111275319120046126195Ozone
1998240163511790044105182Ozone
199720915239108004293185Ozone
199620914746124004293177Ozone
199523918136156104297202Ozone
1994232169391950041101187Ozone
199323718137117103887204Ozone
19922402062482003361161Ozone
199123617838910103993205Ozone
1990616010000163251PM10
1989616100000193644PM10
1988292900000163940PM10
19801649526171412044182269Ozone

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