EnviroNearby

Washington County, Maine air quality history

Daily Air Quality Index summaries from EPA monitors in Washington, Maine, 1984–2025.

91%
Good days in 2025
34
Median daily AQI, 2025
0
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 Washington, Maine on 364 days. 333 of those days (91%) were in the Good range, and the median daily AQI was 34. That median is about the same as the typical monitored county in Maine (median 34 across 11 counties), and lower than 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 rose: an average of 86% in 1984–1988 versus 94% in 2023–2025.

Years with fewer than 120 monitored days (1996, 1997, 1998, 1999, 2000, 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%1984: Good 134 of 174 days1984: Moderate 23 of 174 days1984: Unhealthy for Sensitive Groups 11 of 174 days1984: Unhealthy 5 of 174 days1984: Very Unhealthy 1 of 174 days19841985: Good 142 of 171 days1985: Moderate 19 of 171 days1985: Unhealthy for Sensitive Groups 8 of 171 days1985: Unhealthy 2 of 171 days1986: Good 99 of 104 days1986: Moderate 5 of 104 days1987: Good 109 of 116 days1987: Moderate 7 of 116 days1988: Good 159 of 164 days1988: Moderate 5 of 164 days1989: Good 209 of 229 days1989: Moderate 14 of 229 days1989: Unhealthy for Sensitive Groups 5 of 229 days1989: Unhealthy 1 of 229 days19891990: Good 204 of 225 days1990: Moderate 18 of 225 days1990: Unhealthy for Sensitive Groups 2 of 225 days1990: Unhealthy 1 of 225 days1991: Good 223 of 255 days1991: Moderate 18 of 255 days1991: Unhealthy for Sensitive Groups 7 of 255 days1991: Unhealthy 7 of 255 days1992: Good 213 of 242 days1992: Moderate 17 of 242 days1992: Unhealthy for Sensitive Groups 9 of 242 days1992: Unhealthy 3 of 242 days1993: Good 249 of 270 days1993: Moderate 18 of 270 days1993: Unhealthy for Sensitive Groups 1 of 270 days1993: Unhealthy 2 of 270 days1994: Good 238 of 277 days1994: Moderate 30 of 277 days1994: Unhealthy for Sensitive Groups 9 of 277 days19941995: Good 194 of 226 days1995: Moderate 22 of 226 days1995: Unhealthy for Sensitive Groups 8 of 226 days1995: Unhealthy 2 of 226 days1996: Good 84 of 98 days1996: Moderate 14 of 98 days1997: Good 83 of 101 days1997: Moderate 18 of 101 days1998: Good 88 of 99 days1998: Moderate 11 of 99 days1999: Good 72 of 87 days1999: Moderate 15 of 87 days19992000: Good 91 of 101 days2000: Moderate 10 of 101 days2001: Good 100 of 111 days2001: Moderate 11 of 111 days2002: Good 104 of 120 days2002: Moderate 16 of 120 days2003: Good 106 of 120 days2003: Moderate 14 of 120 days2004: Good 228 of 239 days2004: Moderate 11 of 239 days20042005: Good 313 of 340 days2005: Moderate 25 of 340 days2005: Unhealthy for Sensitive Groups 1 of 340 days2005: Unhealthy 1 of 340 days2006: Good 280 of 304 days2006: Moderate 24 of 304 days2007: Good 338 of 359 days2007: Moderate 17 of 359 days2007: Unhealthy for Sensitive Groups 4 of 359 days2008: Good 337 of 352 days2008: Moderate 15 of 352 days2009: Good 353 of 364 days2009: Moderate 9 of 364 days2009: Unhealthy for Sensitive Groups 2 of 364 days20092010: Good 293 of 301 days2010: Moderate 7 of 301 days2010: Unhealthy for Sensitive Groups 1 of 301 days2011: Good 307 of 316 days2011: Moderate 8 of 316 days2011: Unhealthy for Sensitive Groups 1 of 316 days2012: Good 337 of 342 days2012: Moderate 5 of 342 days2013: Good 346 of 362 days2013: Moderate 15 of 362 days2013: Unhealthy for Sensitive Groups 1 of 362 days2014: Good 355 of 359 days2014: Moderate 4 of 359 days20142015: Good 340 of 356 days2015: Moderate 16 of 356 days2016: Good 360 of 366 days2016: Moderate 6 of 366 days2017: Good 351 of 362 days2017: Moderate 9 of 362 days2017: Unhealthy for Sensitive Groups 2 of 362 days2018: Good 327 of 339 days2018: Moderate 11 of 339 days2018: Unhealthy for Sensitive Groups 1 of 339 days2019: Good 360 of 363 days2019: Moderate 3 of 363 days20192020: Good 351 of 353 days2020: Moderate 2 of 353 days2021: Good 348 of 360 days2021: Moderate 12 of 360 days2022: Good 355 of 364 days2022: Moderate 9 of 364 days2023: Good 343 of 362 days2023: Moderate 19 of 362 days2024: Good 351 of 365 days2024: Moderate 14 of 365 days20242025: Good 333 of 364 days2025: Moderate 31 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 year0501001984: 90th percentile AQI 971985: 90th percentile AQI 771986: 90th percentile AQI 431987: 90th percentile AQI 411988: 90th percentile AQI 361989: 90th percentile AQI 491990: 90th percentile AQI 501991: 90th percentile AQI 611992: 90th percentile AQI 581993: 90th percentile AQI 471994: 90th percentile AQI 581995: 90th percentile AQI 601996: 90th percentile AQI 541997: 90th percentile AQI 561998: 90th percentile AQI 551999: 90th percentile AQI 542000: 90th percentile AQI 482001: 90th percentile AQI 502002: 90th percentile AQI 532003: 90th percentile AQI 522004: 90th percentile AQI 422005: 90th percentile AQI 492006: 90th percentile AQI 482007: 90th percentile AQI 452008: 90th percentile AQI 472009: 90th percentile AQI 452010: 90th percentile AQI 442011: 90th percentile AQI 462012: 90th percentile AQI 442013: 90th percentile AQI 452014: 90th percentile AQI 442015: 90th percentile AQI 452016: 90th percentile AQI 442017: 90th percentile AQI 442018: 90th percentile AQI 462019: 90th percentile AQI 452020: 90th percentile AQI 442021: 90th percentile AQI 442022: 90th percentile AQI 442023: 90th percentile AQI 472024: 90th percentile AQI 442025: 90th percentile AQI 491984: Median AQI 351985: Median AQI 391986: Median AQI 151987: Median AQI 171988: Median AQI 181989: Median AQI 261990: Median AQI 311991: Median AQI 311992: Median AQI 311993: Median AQI 291994: Median AQI 321995: Median AQI 331996: Median AQI 281997: Median AQI 291998: Median AQI 241999: Median AQI 292000: Median AQI 232001: Median AQI 212002: Median AQI 202003: Median AQI 212004: Median AQI 282005: Median AQI 342006: Median AQI 312007: Median AQI 322008: Median AQI 322009: Median AQI 322010: Median AQI 352011: Median AQI 312012: Median AQI 322013: Median AQI 342014: Median AQI 332015: Median AQI 332016: Median AQI 322017: Median AQI 352018: Median AQI 362019: Median AQI 342020: Median AQI 332021: Median AQI 332022: Median AQI 342023: Median AQI 362024: Median AQI 342025: Median AQI 341984198919941999200420092014201920242025
  • 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)7120%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253643333100003449100Ozone
2024365351140000344460Ozone
2023362343190000364774Ozone
202236435590000344458Ozone
2021360348120000334490Ozone
202035335120000334461Ozone
201936336030000344571Ozone
20183393271110003646122Ozone
2017362351920003544147Ozone
201636636060000324474Ozone
2015356340160000334590Ozone
201435935540000334484Ozone
20133623461510003445129Ozone
201234233750000324467Ozone
2011316307810003146105Ozone
2010301293710003544126Ozone
2009364353920003245147Ozone
2008352337150000324780Ozone
20073593381740003245150Ozone
2006304280240000314890Ozone
20053403132511003449159Ozone
2004239228110000284284Ozone
2003120106140000215297PM2.5
2002120104160000205397PM2.5
2001111100110000215092PM2.5
200010191100000234870PM2.5
19998772150000295462PM2.5
19989988110000245588PM2.5
199710183180000295682PM2.5
19969884140000285468PM2.5
19952261942282003360190Ozone
19942772383090003258147Ozone
19932702491812002947174Ozone
19922422131793003158177Ozone
19912552231877003161192Ozone
19902252041821003150177Ozone
19892292091451002649161Ozone
198816415950000183664PM10
198711610970000174169PM10
19861049950000154390PM10
19851711421982003977159Ozone
198417413423115103597203Ozone

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 Maine with a similar median AQI in 2025

All monitored counties in Maine

Source: U.S. EPA AirData, “Annual AQI by County” files for 1984–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem