EnviroNearby

Mercer County, Pennsylvania air quality history

Daily Air Quality Index summaries from EPA monitors in Mercer, Pennsylvania, 1981–2025.

73%
Good days in 2025
42
Median daily AQI, 2025
3
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, Pennsylvania on 365 days. 265 of those days (73%) were in the Good range, and the median daily AQI was 42. That median is about the same as the typical monitored county in Pennsylvania (median 40 across 38 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 262 days. Across the years with fuller monitoring, the share of Good days fell: an average of 83% in 1981–1983 versus 71% 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%1981: Good 239 of 281 days1981: Moderate 25 of 281 days1981: Unhealthy for Sensitive Groups 11 of 281 days1981: Unhealthy 5 of 281 days1981: Very Unhealthy 1 of 281 days19811982: Good 270 of 333 days1982: Moderate 34 of 333 days1982: Unhealthy for Sensitive Groups 19 of 333 days1982: Unhealthy 10 of 333 days1983: Good 272 of 330 days1983: Moderate 29 of 330 days1983: Unhealthy for Sensitive Groups 16 of 330 days1983: Unhealthy 12 of 330 days1983: Very Unhealthy 1 of 330 days1984: Good 254 of 294 days1984: Moderate 23 of 294 days1984: Unhealthy for Sensitive Groups 12 of 294 days1984: Unhealthy 5 of 294 days1985: Good 249 of 336 days1985: Moderate 56 of 336 days1985: Unhealthy for Sensitive Groups 28 of 336 days1985: Unhealthy 3 of 336 days1986: Good 280 of 352 days1986: Moderate 47 of 352 days1986: Unhealthy for Sensitive Groups 22 of 352 days1986: Unhealthy 1 of 352 days1986: Very Unhealthy 2 of 352 days19861987: Good 264 of 362 days1987: Moderate 65 of 362 days1987: Unhealthy for Sensitive Groups 18 of 362 days1987: Unhealthy 15 of 362 days1988: Good 259 of 355 days1988: Moderate 46 of 355 days1988: Unhealthy for Sensitive Groups 19 of 355 days1988: Unhealthy 19 of 355 days1988: Very Unhealthy 12 of 355 days1989: Good 281 of 357 days1989: Moderate 52 of 357 days1989: Unhealthy for Sensitive Groups 19 of 357 days1989: Unhealthy 4 of 357 days1989: Very Unhealthy 1 of 357 days1990: Good 281 of 363 days1990: Moderate 50 of 363 days1990: Unhealthy for Sensitive Groups 25 of 363 days1990: Unhealthy 7 of 363 days1991: Good 251 of 365 days1991: Moderate 56 of 365 days1991: Unhealthy for Sensitive Groups 40 of 365 days1991: Unhealthy 17 of 365 days1991: Very Unhealthy 1 of 365 days19911992: Good 297 of 366 days1992: Moderate 48 of 366 days1992: Unhealthy for Sensitive Groups 15 of 366 days1992: Unhealthy 6 of 366 days1993: Good 279 of 365 days1993: Moderate 45 of 365 days1993: Unhealthy for Sensitive Groups 34 of 365 days1993: Unhealthy 7 of 365 days1994: Good 273 of 363 days1994: Moderate 53 of 363 days1994: Unhealthy for Sensitive Groups 32 of 363 days1994: Unhealthy 5 of 363 days1995: Good 219 of 313 days1995: Moderate 57 of 313 days1995: Unhealthy for Sensitive Groups 27 of 313 days1995: Unhealthy 10 of 313 days1996: Good 208 of 288 days1996: Moderate 48 of 288 days1996: Unhealthy for Sensitive Groups 23 of 288 days1996: Unhealthy 9 of 288 days19961997: Good 292 of 362 days1997: Moderate 45 of 362 days1997: Unhealthy for Sensitive Groups 16 of 362 days1997: Unhealthy 9 of 362 days1998: Good 239 of 350 days1998: Moderate 61 of 350 days1998: Unhealthy for Sensitive Groups 27 of 350 days1998: Unhealthy 19 of 350 days1998: Very Unhealthy 4 of 350 days1999: Good 264 of 365 days1999: Moderate 71 of 365 days1999: Unhealthy for Sensitive Groups 21 of 365 days1999: Unhealthy 9 of 365 days2000: Good 280 of 366 days2000: Moderate 70 of 366 days2000: Unhealthy for Sensitive Groups 14 of 366 days2000: Unhealthy 2 of 366 days2001: Good 122 of 365 days2001: Moderate 193 of 365 days2001: Unhealthy for Sensitive Groups 36 of 365 days2001: Unhealthy 14 of 365 days20012002: Good 115 of 365 days2002: Moderate 211 of 365 days2002: Unhealthy for Sensitive Groups 18 of 365 days2002: Unhealthy 20 of 365 days2002: Very Unhealthy 1 of 365 days2003: Good 109 of 365 days2003: Moderate 241 of 365 days2003: Unhealthy for Sensitive Groups 10 of 365 days2003: Unhealthy 4 of 365 days2003: Very Unhealthy 1 of 365 days2004: Good 137 of 366 days2004: Moderate 215 of 366 days2004: Unhealthy for Sensitive Groups 13 of 366 days2004: Unhealthy 1 of 366 days2005: Good 114 of 365 days2005: Moderate 214 of 365 days2005: Unhealthy for Sensitive Groups 33 of 365 days2005: Unhealthy 4 of 365 days2006: Good 147 of 365 days2006: Moderate 204 of 365 days2006: Unhealthy for Sensitive Groups 11 of 365 days2006: Unhealthy 3 of 365 days20062007: Good 134 of 365 days2007: Moderate 208 of 365 days2007: Unhealthy for Sensitive Groups 21 of 365 days2007: Unhealthy 2 of 365 days2008: Good 158 of 366 days2008: Moderate 193 of 366 days2008: Unhealthy for Sensitive Groups 15 of 366 days2009: Good 159 of 365 days2009: Moderate 200 of 365 days2009: Unhealthy for Sensitive Groups 6 of 365 days2010: Good 173 of 365 days2010: Moderate 180 of 365 days2010: Unhealthy for Sensitive Groups 12 of 365 days2011: Good 175 of 365 days2011: Moderate 182 of 365 days2011: Unhealthy for Sensitive Groups 8 of 365 days20112012: Good 124 of 366 days2012: Moderate 217 of 366 days2012: Unhealthy for Sensitive Groups 20 of 366 days2012: Unhealthy 5 of 366 days2013: Good 143 of 365 days2013: Moderate 219 of 365 days2013: Unhealthy for Sensitive Groups 3 of 365 days2014: Good 114 of 365 days2014: Moderate 247 of 365 days2014: Unhealthy for Sensitive Groups 4 of 365 days2015: Good 159 of 365 days2015: Moderate 203 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days2015: Unhealthy 1 of 365 days2016: Good 203 of 366 days2016: Moderate 160 of 366 days2016: Unhealthy for Sensitive Groups 3 of 366 days20162017: Good 89 of 365 days2017: Moderate 274 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2018: Good 240 of 365 days2018: Moderate 122 of 365 days2018: Unhealthy for Sensitive Groups 3 of 365 days2019: Good 240 of 365 days2019: Moderate 125 of 365 days2020: Good 272 of 366 days2020: Moderate 93 of 366 days2020: Unhealthy for Sensitive Groups 1 of 366 days2021: Good 277 of 363 days2021: Moderate 85 of 363 days2021: Unhealthy for Sensitive Groups 1 of 363 days20212022: Good 288 of 365 days2022: Moderate 74 of 365 days2022: Unhealthy for Sensitive Groups 3 of 365 days2023: Good 237 of 364 days2023: Moderate 122 of 364 days2023: Unhealthy for Sensitive Groups 3 of 364 days2023: Unhealthy 2 of 364 days2024: Good 274 of 366 days2024: Moderate 92 of 366 days2025: Good 265 of 365 days2025: Moderate 97 of 365 days2025: Unhealthy for Sensitive Groups 3 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 year0501001501981: 90th percentile AQI 711982: 90th percentile AQI 931983: 90th percentile AQI 971984: 90th percentile AQI 741985: 90th percentile AQI 971986: 90th percentile AQI 901987: 90th percentile AQI 1001988: 90th percentile AQI 1401989: 90th percentile AQI 841990: 90th percentile AQI 901991: 90th percentile AQI 1261992: 90th percentile AQI 741993: 90th percentile AQI 1081994: 90th percentile AQI 1011995: 90th percentile AQI 1081996: 90th percentile AQI 1011997: 90th percentile AQI 801998: 90th percentile AQI 1291999: 90th percentile AQI 972000: 90th percentile AQI 842001: 90th percentile AQI 1222002: 90th percentile AQI 1052003: 90th percentile AQI 832004: 90th percentile AQI 872005: 90th percentile AQI 1012006: 90th percentile AQI 842007: 90th percentile AQI 902008: 90th percentile AQI 872009: 90th percentile AQI 722010: 90th percentile AQI 772011: 90th percentile AQI 762012: 90th percentile AQI 872013: 90th percentile AQI 732014: 90th percentile AQI 712015: 90th percentile AQI 712016: 90th percentile AQI 692017: 90th percentile AQI 682018: 90th percentile AQI 662019: 90th percentile AQI 612020: 90th percentile AQI 582021: 90th percentile AQI 612022: 90th percentile AQI 552023: 90th percentile AQI 672024: 90th percentile AQI 612025: 90th percentile AQI 641981: Median AQI 261982: Median AQI 301983: Median AQI 281984: Median AQI 251985: Median AQI 331986: Median AQI 351987: Median AQI 351988: Median AQI 351989: Median AQI 341990: Median AQI 361991: Median AQI 391992: Median AQI 341993: Median AQI 351994: Median AQI 381995: Median AQI 401996: Median AQI 381997: Median AQI 351998: Median AQI 411999: Median AQI 382000: Median AQI 382001: Median AQI 582002: Median AQI 572003: Median AQI 562004: Median AQI 552005: Median AQI 582006: Median AQI 542007: Median AQI 562008: Median AQI 532009: Median AQI 532010: Median AQI 522011: Median AQI 512012: Median AQI 562013: Median AQI 532014: Median AQI 552015: Median AQI 532016: Median AQI 482017: Median AQI 552018: Median AQI 432019: Median AQI 442020: Median AQI 412021: Median AQI 402022: Median AQI 402023: Median AQI 442024: Median AQI 402025: Median AQI 421981198619911996200120062011201620212025
  • 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
Ozone26272%
Fine particles (PM2.5)10328%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652659730004264115Ozone
2024366274920000406197Ozone
202336423712232004467196Ozone
20223652887430004055136Ozone
20213632778510004061112Ozone
20203662729310004158105Ozone
20193652401250000446196PM2.5
201836524012230004366115Ozone
20173658927420005568108PM2.5
201636620316030004869143Ozone
201536515920321005371153PM2.5
201436511424740005571115PM2.5
201336514321930005373147PM2.5
2012366124217205005687177PM2.5
201136517518280005176150PM2.5
2010365173180120005277140Ozone
200936515920060005372119PM2.5
2008366158193150005387150PM2.5
2007365134208212005690156PM2.5
2006365147204113005484174PM2.5
20053651142143340058101177PM2.5
2004366137215131005587151PM2.5
2003365109241104105683210PM2.5
200236511521118201057105201PM2.5
200136512219336140058122200PM2.5
200036628070142003884200Ozone
199936526471219003897174Ozone
19983502396127194041129208Ozone
199736229245169003580185Ozone
1996288208482390038101182Ozone
19953132195727100040108192Ozone
1994363273533250038101195Ozone
1993365279453470035108190Ozone
199236629748156003474197Ozone
19913652515640171039126205Ozone
199036328150257003690187Ozone
198935728152194103484201Ozone
198835525946191912035140224Ozone
19873622646518150035100192Ozone
198635228047221203590207Ozone
198533624956283003397161Ozone
198429425423125002574185Ozone
1983330272291612102897215Ozone
1982333270341910003093197Ozone
198128123925115102671227Ozone

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 Pennsylvania with a similar median AQI in 2025

All monitored counties in Pennsylvania

Source: U.S. EPA AirData, “Annual AQI by County” files for 1981–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem