EnviroNearby

Mercer County, North Dakota air quality history

Daily Air Quality Index summaries from EPA monitors in Mercer, North Dakota, 1980–2025.

80%
Good days in 2025
37
Median daily AQI, 2025
10
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 Mercer, North Dakota on 365 days. 293 of those days (80%) were in the Good range, and the median daily AQI was 37. That median is about the same as the typical monitored county in North Dakota (median 38 across 9 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 245 days. Across the years with fuller monitoring, the share of Good days fell: an average of 91% in 1980–1982 versus 77% 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 312 of 366 days1980: Moderate 48 of 366 days1980: Unhealthy for Sensitive Groups 6 of 366 days19801981: Good 349 of 365 days1981: Moderate 15 of 365 days1981: Unhealthy for Sensitive Groups 1 of 365 days1982: Good 340 of 365 days1982: Moderate 25 of 365 days1983: Good 318 of 365 days1983: Moderate 42 of 365 days1983: Unhealthy for Sensitive Groups 5 of 365 days1984: Good 334 of 366 days1984: Moderate 32 of 366 days1985: Good 355 of 365 days1985: Moderate 10 of 365 days19851986: Good 339 of 365 days1986: Moderate 25 of 365 days1986: Unhealthy for Sensitive Groups 1 of 365 days1987: Good 317 of 365 days1987: Moderate 46 of 365 days1987: Unhealthy for Sensitive Groups 2 of 365 days1988: Good 307 of 366 days1988: Moderate 53 of 366 days1988: Unhealthy for Sensitive Groups 6 of 366 days1989: Good 302 of 365 days1989: Moderate 53 of 365 days1989: Unhealthy for Sensitive Groups 8 of 365 days1989: Unhealthy 2 of 365 days1990: Good 350 of 365 days1990: Moderate 15 of 365 days19901991: Good 351 of 365 days1991: Moderate 14 of 365 days1992: Good 343 of 366 days1992: Moderate 21 of 366 days1992: Unhealthy for Sensitive Groups 2 of 366 days1993: Good 358 of 365 days1993: Moderate 6 of 365 days1993: Unhealthy for Sensitive Groups 1 of 365 days1994: Good 357 of 365 days1994: Moderate 7 of 365 days1994: Unhealthy for Sensitive Groups 1 of 365 days1995: Good 356 of 365 days1995: Moderate 8 of 365 days1995: Unhealthy for Sensitive Groups 1 of 365 days19951996: Good 347 of 366 days1996: Moderate 19 of 366 days1997: Good 337 of 365 days1997: Moderate 24 of 365 days1997: Unhealthy for Sensitive Groups 4 of 365 days1998: Good 320 of 365 days1998: Moderate 39 of 365 days1998: Unhealthy for Sensitive Groups 6 of 365 days1999: Good 345 of 365 days1999: Moderate 19 of 365 days1999: Unhealthy for Sensitive Groups 1 of 365 days2000: Good 354 of 366 days2000: Moderate 12 of 366 days20002001: Good 347 of 365 days2001: Moderate 18 of 365 days2002: Good 338 of 365 days2002: Moderate 27 of 365 days2003: Good 332 of 365 days2003: Moderate 33 of 365 days2004: Good 358 of 366 days2004: Moderate 8 of 366 days2005: Good 344 of 364 days2005: Moderate 20 of 364 days20052006: Good 313 of 365 days2006: Moderate 50 of 365 days2006: Unhealthy for Sensitive Groups 2 of 365 days2007: Good 345 of 365 days2007: Moderate 20 of 365 days2008: Good 326 of 366 days2008: Moderate 40 of 366 days2009: Good 355 of 365 days2009: Moderate 10 of 365 days2010: Good 293 of 365 days2010: Moderate 72 of 365 days20102011: Good 262 of 365 days2011: Moderate 103 of 365 days2012: Good 301 of 366 days2012: Moderate 65 of 366 days2013: Good 300 of 365 days2013: Moderate 65 of 365 days2014: Good 324 of 363 days2014: Moderate 38 of 363 days2014: Unhealthy for Sensitive Groups 1 of 363 days2015: Good 297 of 365 days2015: Moderate 62 of 365 days2015: Unhealthy for Sensitive Groups 4 of 365 days2015: Unhealthy 2 of 365 days20152016: Good 356 of 366 days2016: Moderate 9 of 366 days2016: Unhealthy for Sensitive Groups 1 of 366 days2017: Good 317 of 365 days2017: Moderate 46 of 365 days2017: Unhealthy for Sensitive Groups 1 of 365 days2017: Unhealthy 1 of 365 days2018: Good 305 of 365 days2018: Moderate 58 of 365 days2018: Unhealthy for Sensitive Groups 2 of 365 days2019: Good 301 of 365 days2019: Moderate 64 of 365 days2020: Good 328 of 366 days2020: Moderate 38 of 366 days20202021: Good 279 of 365 days2021: Moderate 77 of 365 days2021: Unhealthy for Sensitive Groups 5 of 365 days2021: Unhealthy 4 of 365 days2022: Good 318 of 365 days2022: Moderate 47 of 365 days2023: Good 252 of 365 days2023: Moderate 97 of 365 days2023: Unhealthy for Sensitive Groups 10 of 365 days2023: Unhealthy 5 of 365 days2023: Hazardous 1 of 365 days2024: Good 304 of 366 days2024: Moderate 56 of 366 days2024: Unhealthy for Sensitive Groups 4 of 366 days2024: Unhealthy 2 of 366 days2025: Good 293 of 365 days2025: Moderate 62 of 365 days2025: Unhealthy for Sensitive Groups 6 of 365 days2025: Unhealthy 3 of 365 days2025: Very 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 581981: 90th percentile AQI 441982: 90th percentile AQI 481983: 90th percentile AQI 611984: 90th percentile AQI 501985: 90th percentile AQI 451986: 90th percentile AQI 481987: 90th percentile AQI 611988: 90th percentile AQI 641989: 90th percentile AQI 641990: 90th percentile AQI 471991: 90th percentile AQI 471992: 90th percentile AQI 471993: 90th percentile AQI 421994: 90th percentile AQI 451995: 90th percentile AQI 441996: 90th percentile AQI 451997: 90th percentile AQI 481998: 90th percentile AQI 521999: 90th percentile AQI 442000: 90th percentile AQI 462001: 90th percentile AQI 472002: 90th percentile AQI 492003: 90th percentile AQI 502004: 90th percentile AQI 442005: 90th percentile AQI 462006: 90th percentile AQI 542007: 90th percentile AQI 462008: 90th percentile AQI 522009: 90th percentile AQI 472010: 90th percentile AQI 562011: 90th percentile AQI 552012: 90th percentile AQI 552013: 90th percentile AQI 542014: 90th percentile AQI 512015: 90th percentile AQI 562016: 90th percentile AQI 442017: 90th percentile AQI 532018: 90th percentile AQI 582019: 90th percentile AQI 532020: 90th percentile AQI 512021: 90th percentile AQI 682022: 90th percentile AQI 522023: 90th percentile AQI 732024: 90th percentile AQI 582025: 90th percentile AQI 591980: Median AQI 351981: Median AQI 331982: Median AQI 331983: Median AQI 381984: Median AQI 371985: Median AQI 361986: Median AQI 341987: Median AQI 321988: Median AQI 371989: Median AQI 361990: Median AQI 331991: Median AQI 341992: Median AQI 311993: Median AQI 311994: Median AQI 271995: Median AQI 261996: Median AQI 271997: Median AQI 291998: Median AQI 361999: Median AQI 322000: Median AQI 322001: Median AQI 332002: Median AQI 332003: Median AQI 342004: Median AQI 332005: Median AQI 332006: Median AQI 352007: Median AQI 322008: Median AQI 362009: Median AQI 342010: Median AQI 402011: Median AQI 442012: Median AQI 402013: Median AQI 392014: Median AQI 372015: Median AQI 372016: Median AQI 322017: Median AQI 352018: Median AQI 382019: Median AQI 382020: Median AQI 362021: Median AQI 382022: Median AQI 362023: Median AQI 412024: Median AQI 372025: Median AQI 371980198519901995200020052010201520202025
  • 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
Ozone24567%
Fine particles (PM2.5)12033%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652936263103759283Ozone
20243663045642003758167Ozone
202336525297105014173322Ozone
2022365318470000365272Ozone
20213652797754003868174Ozone
2020366328380000365178Ozone
2019365301640000385372Ozone
20183653055820003858111Ozone
20173653174611003553159Ozone
2016366356910003244107Ozone
20153652976242003756152Ozone
20143633243810003751128Ozone
2013365300650000395476Ozone
2012366301650000405587Ozone
20113652621030000445574Ozone
2010365293720000405687Ozone
2009365355100000344767Ozone
2008366326400000365277Ozone
2007365345200000324674Ozone
20063653135020003554115Ozone
2005364344200000334669Ozone
200436635880000334460Ozone
2003365332330000345093Ozone
2002365338270000334993Ozone
2001365347180000334783Ozone
2000366354120000324694Ozone
19993653451910003244102Ozone
19983653203960003652116Ozone
19973653372440002948121NO2
1996366347190000274587NO2
1995365356810002644103NO2
1994365357710002745101NO2
1993365358610003142102Ozone
19923663432120003147108Ozone
1991365351140000344767Ozone
1990365350150000334774Ozone
19893653025382003664169Ozone
19883663075360003764119Ozone
19873653174620003261133Ozone
19863653392510003448108Ozone
1985365355100000364593Ozone
1984366334320000375090Ozone
19833653184250003861108Ozone
1982365340250000334893Ozone
19813653491510003344112Ozone
19803663124860003558126Ozone

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 North Dakota with a similar median AQI in 2025

All monitored counties in North Dakota

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