EnviroNearby

Centre County, Pennsylvania air quality history

Daily Air Quality Index summaries from EPA monitors in Centre, Pennsylvania, 1990–2025.

74%
Good days in 2025
41
Median daily AQI, 2025
1
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 Centre, Pennsylvania on 365 days. 271 of those days (74%) were in the Good range, and the median daily AQI was 41. 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 247 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 73% in 1990–1992 versus 73% 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%1990: Good 271 of 360 days1990: Moderate 57 of 360 days1990: Unhealthy for Sensitive Groups 24 of 360 days1990: Unhealthy 8 of 360 days19901991: Good 234 of 354 days1991: Moderate 68 of 354 days1991: Unhealthy for Sensitive Groups 39 of 354 days1991: Unhealthy 10 of 354 days1991: Very Unhealthy 3 of 354 days1992: Good 285 of 362 days1992: Moderate 58 of 362 days1992: Unhealthy for Sensitive Groups 14 of 362 days1992: Unhealthy 5 of 362 days1993: Good 253 of 352 days1993: Moderate 61 of 352 days1993: Unhealthy for Sensitive Groups 27 of 352 days1993: Unhealthy 11 of 352 days1994: Good 269 of 364 days1994: Moderate 69 of 364 days1994: Unhealthy for Sensitive Groups 21 of 364 days1994: Unhealthy 5 of 364 days1995: Good 264 of 354 days1995: Moderate 61 of 354 days1995: Unhealthy for Sensitive Groups 23 of 354 days1995: Unhealthy 6 of 354 days19951996: Good 274 of 363 days1996: Moderate 64 of 363 days1996: Unhealthy for Sensitive Groups 23 of 363 days1996: Unhealthy 2 of 363 days1997: Good 278 of 364 days1997: Moderate 56 of 364 days1997: Unhealthy for Sensitive Groups 21 of 364 days1997: Unhealthy 6 of 364 days1997: Very Unhealthy 3 of 364 days1998: Good 214 of 317 days1998: Moderate 73 of 317 days1998: Unhealthy for Sensitive Groups 22 of 317 days1998: Unhealthy 8 of 317 days1999: Good 248 of 364 days1999: Moderate 82 of 364 days1999: Unhealthy for Sensitive Groups 24 of 364 days1999: Unhealthy 10 of 364 days2000: Good 268 of 366 days2000: Moderate 79 of 366 days2000: Unhealthy for Sensitive Groups 16 of 366 days2000: Unhealthy 3 of 366 days20002001: Good 136 of 365 days2001: Moderate 192 of 365 days2001: Unhealthy for Sensitive Groups 31 of 365 days2001: Unhealthy 6 of 365 days2002: Good 155 of 365 days2002: Moderate 164 of 365 days2002: Unhealthy for Sensitive Groups 31 of 365 days2002: Unhealthy 13 of 365 days2002: Very Unhealthy 2 of 365 days2003: Good 117 of 365 days2003: Moderate 228 of 365 days2003: Unhealthy for Sensitive Groups 16 of 365 days2003: Unhealthy 2 of 365 days2003: Very Unhealthy 2 of 365 days2004: Good 132 of 366 days2004: Moderate 219 of 366 days2004: Unhealthy for Sensitive Groups 15 of 366 days2005: Good 137 of 365 days2005: Moderate 202 of 365 days2005: Unhealthy for Sensitive Groups 23 of 365 days2005: Unhealthy 3 of 365 days20052006: Good 161 of 365 days2006: Moderate 190 of 365 days2006: Unhealthy for Sensitive Groups 14 of 365 days2007: Good 153 of 365 days2007: Moderate 195 of 365 days2007: Unhealthy for Sensitive Groups 17 of 365 days2008: Good 172 of 366 days2008: Moderate 183 of 366 days2008: Unhealthy for Sensitive Groups 11 of 366 days2009: Good 201 of 365 days2009: Moderate 164 of 365 days2010: Good 187 of 365 days2010: Moderate 170 of 365 days2010: Unhealthy for Sensitive Groups 8 of 365 days20102011: Good 183 of 365 days2011: Moderate 173 of 365 days2011: Unhealthy for Sensitive Groups 9 of 365 days2012: Good 140 of 366 days2012: Moderate 217 of 366 days2012: Unhealthy for Sensitive Groups 8 of 366 days2012: Unhealthy 1 of 366 days2013: Good 210 of 365 days2013: Moderate 153 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 177 of 365 days2014: Moderate 188 of 365 days2015: Good 204 of 365 days2015: Moderate 159 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days20152016: Good 232 of 366 days2016: Moderate 132 of 366 days2016: Unhealthy for Sensitive Groups 2 of 366 days2017: Good 174 of 365 days2017: Moderate 191 of 365 days2018: Good 225 of 365 days2018: Moderate 138 of 365 days2018: Unhealthy for Sensitive Groups 2 of 365 days2019: Good 192 of 365 days2019: Moderate 173 of 365 days2020: Good 287 of 366 days2020: Moderate 79 of 366 days20202021: Good 241 of 365 days2021: Moderate 123 of 365 days2021: Unhealthy for Sensitive Groups 1 of 365 days2022: Good 240 of 365 days2022: Moderate 125 of 365 days2023: Good 239 of 365 days2023: Moderate 118 of 365 days2023: Unhealthy for Sensitive Groups 3 of 365 days2023: Unhealthy 5 of 365 days2024: Good 287 of 366 days2024: Moderate 79 of 366 days2025: Good 271 of 365 days2025: Moderate 93 of 365 days2025: Unhealthy for Sensitive Groups 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 year0501001501990: 90th percentile AQI 971991: 90th percentile AQI 1221992: 90th percentile AQI 801993: 90th percentile AQI 1051994: 90th percentile AQI 931995: 90th percentile AQI 971996: 90th percentile AQI 841997: 90th percentile AQI 841998: 90th percentile AQI 1001999: 90th percentile AQI 1002000: 90th percentile AQI 742001: 90th percentile AQI 1012002: 90th percentile AQI 1152003: 90th percentile AQI 862004: 90th percentile AQI 832005: 90th percentile AQI 952006: 90th percentile AQI 872007: 90th percentile AQI 862008: 90th percentile AQI 802009: 90th percentile AQI 672010: 90th percentile AQI 772011: 90th percentile AQI 762012: 90th percentile AQI 772013: 90th percentile AQI 662014: 90th percentile AQI 672015: 90th percentile AQI 692016: 90th percentile AQI 632017: 90th percentile AQI 642018: 90th percentile AQI 632019: 90th percentile AQI 662020: 90th percentile AQI 572021: 90th percentile AQI 642022: 90th percentile AQI 592023: 90th percentile AQI 682024: 90th percentile AQI 582025: 90th percentile AQI 581990: Median AQI 381991: Median AQI 381992: Median AQI 341993: Median AQI 381994: Median AQI 381995: Median AQI 371996: Median AQI 381997: Median AQI 381998: Median AQI 421999: Median AQI 422000: Median AQI 402001: Median AQI 562002: Median AQI 542003: Median AQI 582004: Median AQI 552005: Median AQI 562006: Median AQI 542007: Median AQI 542008: Median AQI 522009: Median AQI 472010: Median AQI 502011: Median AQI 502012: Median AQI 542013: Median AQI 472014: Median AQI 512015: Median AQI 462016: Median AQI 452017: Median AQI 512018: Median AQI 442019: Median AQI 492020: Median AQI 412021: Median AQI 432022: Median AQI 442023: Median AQI 452024: Median AQI 402025: Median AQI 4119901995200020052010201520202025
  • 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
Ozone24768%
Fine particles (PM2.5)11832%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652719310004158101Ozone
2024366287790000405897Ozone
202336523911835004568199Ozone
20223652401250000445989PM2.5
202136524112310004364114PM2.5
2020366287790000415791Ozone
20193651921730000496699PM2.5
201836522513820004463122PM2.5
201736517419100005164100PM2.5
201636623213220004563122Ozone
201536520415920004669108PM2.5
20143651771880000516790PM2.5
201336521015320004766112PM2.5
201236614021781005477154PM2.5
201136518317390005076143PM2.5
201036518717080005077133PM2.5
200936520116400004767100PM2.5
2008366172183110005280136PM2.5
2007365153195170005486140PM2.5
2006365161190140005487126PM2.5
2005365137202233005695161PM2.5
2004366132219150005583146PM2.5
2003365117228162205886202PM2.5
200236515516431132054115202Ozone
20013651361923160056101174PM2.5
200036626879163004074197Ozone
19993642488224100042100185Ozone
1998317214732280042100195Ozone
199736427856216303884213Ozone
199636327464232003884177Ozone
199535426461236003797197Ozone
199436426969215003893187Ozone
19933522536127110038105190Ozone
199236228558145003480182Ozone
19913542346839103038122207Ozone
199036027157248003897190Ozone

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 1990–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem