EnviroNearby

Somerset County, Pennsylvania air quality history

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

95%
Good days in 2025
36
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 Somerset, Pennsylvania on 364 days. 344 of those days (95%) were in the Good range, and the median daily AQI was 36. That median is lower than the typical monitored county in Pennsylvania (median 40 across 38 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 364 days. Across the years with fuller monitoring, the share of Good days rose: an average of 77% in 1990–1992 versus 92% 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 283 of 361 days1990: Moderate 54 of 361 days1990: Unhealthy for Sensitive Groups 20 of 361 days1990: Unhealthy 4 of 361 days19901991: Good 236 of 354 days1991: Moderate 76 of 354 days1991: Unhealthy for Sensitive Groups 35 of 354 days1991: Unhealthy 7 of 354 days1992: Good 308 of 363 days1992: Moderate 48 of 363 days1992: Unhealthy for Sensitive Groups 6 of 363 days1992: Unhealthy 1 of 363 days1993: Good 272 of 362 days1993: Moderate 63 of 362 days1993: Unhealthy for Sensitive Groups 20 of 362 days1993: Unhealthy 7 of 362 days1994: Good 277 of 360 days1994: Moderate 61 of 360 days1994: Unhealthy for Sensitive Groups 19 of 360 days1994: Unhealthy 3 of 360 days1995: Good 172 of 268 days1995: Moderate 65 of 268 days1995: Unhealthy for Sensitive Groups 24 of 268 days1995: Unhealthy 7 of 268 days19951996: Good 159 of 213 days1996: Moderate 40 of 213 days1996: Unhealthy for Sensitive Groups 13 of 213 days1996: Unhealthy 1 of 213 days1997: Good 287 of 360 days1997: Moderate 53 of 360 days1997: Unhealthy for Sensitive Groups 14 of 360 days1997: Unhealthy 6 of 360 days1998: Good 271 of 356 days1998: Moderate 63 of 356 days1998: Unhealthy for Sensitive Groups 17 of 356 days1998: Unhealthy 5 of 356 days1999: Good 295 of 356 days1999: Moderate 51 of 356 days1999: Unhealthy for Sensitive Groups 9 of 356 days1999: Unhealthy 1 of 356 days2000: Good 309 of 331 days2000: Moderate 22 of 331 days20002001: Good 295 of 356 days2001: Moderate 51 of 356 days2001: Unhealthy for Sensitive Groups 10 of 356 days2002: Good 281 of 359 days2002: Moderate 53 of 359 days2002: Unhealthy for Sensitive Groups 22 of 359 days2002: Unhealthy 3 of 359 days2003: Good 298 of 335 days2003: Moderate 32 of 335 days2003: Unhealthy for Sensitive Groups 5 of 335 days2004: Good 335 of 359 days2004: Moderate 23 of 359 days2004: Unhealthy for Sensitive Groups 1 of 359 days2005: Good 290 of 362 days2005: Moderate 61 of 362 days2005: Unhealthy for Sensitive Groups 10 of 362 days2005: Unhealthy 1 of 362 days20052006: Good 278 of 348 days2006: Moderate 62 of 348 days2006: Unhealthy for Sensitive Groups 8 of 348 days2007: Good 271 of 341 days2007: Moderate 64 of 341 days2007: Unhealthy for Sensitive Groups 6 of 341 days2008: Good 316 of 360 days2008: Moderate 43 of 360 days2008: Unhealthy for Sensitive Groups 1 of 360 days2009: Good 317 of 349 days2009: Moderate 31 of 349 days2009: Unhealthy for Sensitive Groups 1 of 349 days2010: Good 300 of 364 days2010: Moderate 58 of 364 days2010: Unhealthy for Sensitive Groups 6 of 364 days20102011: Good 310 of 342 days2011: Moderate 31 of 342 days2011: Unhealthy for Sensitive Groups 1 of 342 days2012: Good 273 of 318 days2012: Moderate 43 of 318 days2012: Unhealthy for Sensitive Groups 2 of 318 days2013: Good 294 of 318 days2013: Moderate 23 of 318 days2013: Unhealthy for Sensitive Groups 1 of 318 days2014: Good 346 of 362 days2014: Moderate 16 of 362 days2015: Good 272 of 287 days2015: Moderate 15 of 287 days20152016: Good 324 of 357 days2016: Moderate 32 of 357 days2016: Unhealthy for Sensitive Groups 1 of 357 days2017: Good 342 of 363 days2017: Moderate 21 of 363 days2018: Good 330 of 357 days2018: Moderate 27 of 357 days2019: Good 340 of 359 days2019: Moderate 19 of 359 days2020: Good 357 of 365 days2020: Moderate 8 of 365 days20202021: Good 339 of 363 days2021: Moderate 24 of 363 days2022: Good 351 of 360 days2022: Moderate 9 of 360 days2023: Good 333 of 365 days2023: Moderate 32 of 365 days2024: Good 323 of 358 days2024: Moderate 35 of 358 days2025: Good 344 of 364 days2025: Moderate 20 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 year0501001501990: 90th percentile AQI 871991: 90th percentile AQI 1081992: 90th percentile AQI 641993: 90th percentile AQI 901994: 90th percentile AQI 901995: 90th percentile AQI 1081996: 90th percentile AQI 931997: 90th percentile AQI 871998: 90th percentile AQI 871999: 90th percentile AQI 612000: 90th percentile AQI 482001: 90th percentile AQI 672002: 90th percentile AQI 872003: 90th percentile AQI 542004: 90th percentile AQI 472005: 90th percentile AQI 712006: 90th percentile AQI 742007: 90th percentile AQI 672008: 90th percentile AQI 542009: 90th percentile AQI 502010: 90th percentile AQI 642011: 90th percentile AQI 492012: 90th percentile AQI 582013: 90th percentile AQI 492014: 90th percentile AQI 472015: 90th percentile AQI 482016: 90th percentile AQI 502017: 90th percentile AQI 472018: 90th percentile AQI 472019: 90th percentile AQI 482020: 90th percentile AQI 442021: 90th percentile AQI 472022: 90th percentile AQI 452023: 90th percentile AQI 492024: 90th percentile AQI 502025: 90th percentile AQI 461990: Median AQI 361991: Median AQI 391992: Median AQI 341993: Median AQI 351994: Median AQI 361995: Median AQI 441996: Median AQI 381997: Median AQI 371998: Median AQI 371999: Median AQI 322000: Median AQI 312001: Median AQI 362002: Median AQI 362003: Median AQI 332004: Median AQI 322005: Median AQI 362006: Median AQI 372007: Median AQI 362008: Median AQI 352009: Median AQI 332010: Median AQI 372011: Median AQI 362012: Median AQI 362013: Median AQI 352014: Median AQI 362015: Median AQI 342016: Median AQI 362017: Median AQI 362018: Median AQI 332019: Median AQI 362020: Median AQI 342021: Median AQI 342022: Median AQI 342023: Median AQI 352024: Median AQI 372025: Median AQI 3619901995200020052010201520202025
  • 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
Ozone364100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025364344200000364693Ozone
2024358323350000375090Ozone
2023365333320000354993Ozone
202236035190000344590Ozone
2021363339240000344790Ozone
202036535780000344471Ozone
2019359340190000364880Ozone
2018357330270000334790Ozone
2017363342210000364797Ozone
20163573243210003650105Ozone
2015287272150000344877Ozone
2014362346160000364797Ozone
20133182942310003549105Ozone
20123182734320003658140Ozone
20113423103110003649115Ozone
20103643005860003764126Ozone
20093493173110003350108Ozone
20083603164310003554108Ozone
20073412716460003667122Ozone
20063482786280003774112Ozone
200536229061101003671154Ozone
20043593352310003247119Ozone
20033352983250003354136Ozone
200235928153223003687166Ozone
200135629551100003667126Ozone
2000331309220000314890Ozone
19993562955191003261151Ozone
199835627163175003787182Ozone
199736028753146003787190Ozone
199621315940131003893151Ozone
1995268172652470044108187Ozone
199436027761193003690190Ozone
199336227263207003590174Ozone
19923633084861003464156Ozone
1991354236763570039108187Ozone
199036128354204003687190Ozone

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