EnviroNearby

Westmoreland County, Pennsylvania air quality history

Daily Air Quality Index summaries from EPA monitors in Westmoreland, Pennsylvania, 1980–2025.

78%
Good days in 2025
39
Median daily AQI, 2025
1
Days above 100 in 2025
362
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Westmoreland, Pennsylvania on 362 days. 283 of those days (78%) were in the Good range, and the median daily AQI was 39. 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 232 days. Across the years with fuller monitoring, the share of Good days fell: an average of 80% in 1981–1991 versus 77% in 2023–2025.

Years with fewer than 120 monitored days (1980, 1982, 1989) 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%1980: Good 38 of 41 days1980: Moderate 3 of 41 days19801981: Good 136 of 162 days1981: Moderate 13 of 162 days1981: Unhealthy for Sensitive Groups 7 of 162 days1981: Unhealthy 3 of 162 days1981: Very Unhealthy 3 of 162 days1982: Good 22 of 22 days1989: Good 40 of 52 days1989: Moderate 12 of 52 days1990: Good 186 of 222 days1990: Moderate 27 of 222 days1990: Unhealthy for Sensitive Groups 7 of 222 days1990: Unhealthy 2 of 222 days1991: Good 173 of 242 days1991: Moderate 52 of 242 days1991: Unhealthy for Sensitive Groups 14 of 242 days1991: Unhealthy 3 of 242 days19911992: Good 212 of 223 days1992: Moderate 10 of 223 days1992: Unhealthy for Sensitive Groups 1 of 223 days1993: Good 169 of 227 days1993: Moderate 42 of 227 days1993: Unhealthy for Sensitive Groups 11 of 227 days1993: Unhealthy 5 of 227 days1994: Good 154 of 195 days1994: Moderate 24 of 195 days1994: Unhealthy for Sensitive Groups 10 of 195 days1994: Unhealthy 7 of 195 days1995: Good 162 of 218 days1995: Moderate 34 of 218 days1995: Unhealthy for Sensitive Groups 15 of 218 days1995: Unhealthy 6 of 218 days1995: Very Unhealthy 1 of 218 days1996: Good 182 of 232 days1996: Moderate 41 of 232 days1996: Unhealthy for Sensitive Groups 8 of 232 days1996: Unhealthy 1 of 232 days19961997: Good 231 of 273 days1997: Moderate 32 of 273 days1997: Unhealthy for Sensitive Groups 6 of 273 days1997: Unhealthy 2 of 273 days1997: Very Unhealthy 2 of 273 days1998: Good 321 of 364 days1998: Moderate 32 of 364 days1998: Unhealthy for Sensitive Groups 8 of 364 days1998: Unhealthy 3 of 364 days1999: Good 227 of 365 days1999: Moderate 95 of 365 days1999: Unhealthy for Sensitive Groups 27 of 365 days1999: Unhealthy 14 of 365 days1999: Very Unhealthy 2 of 365 days2000: Good 244 of 366 days2000: Moderate 110 of 366 days2000: Unhealthy for Sensitive Groups 10 of 366 days2000: Unhealthy 2 of 366 days2001: Good 203 of 365 days2001: Moderate 127 of 365 days2001: Unhealthy for Sensitive Groups 33 of 365 days2001: Unhealthy 2 of 365 days20012002: Good 215 of 365 days2002: Moderate 116 of 365 days2002: Unhealthy for Sensitive Groups 23 of 365 days2002: Unhealthy 10 of 365 days2002: Very Unhealthy 1 of 365 days2003: Good 227 of 365 days2003: Moderate 128 of 365 days2003: Unhealthy for Sensitive Groups 6 of 365 days2003: Unhealthy 3 of 365 days2003: Very Unhealthy 1 of 365 days2004: Good 238 of 366 days2004: Moderate 121 of 366 days2004: Unhealthy for Sensitive Groups 6 of 366 days2004: Unhealthy 1 of 366 days2005: Good 214 of 365 days2005: Moderate 128 of 365 days2005: Unhealthy for Sensitive Groups 18 of 365 days2005: Unhealthy 5 of 365 days2006: Good 241 of 365 days2006: Moderate 106 of 365 days2006: Unhealthy for Sensitive Groups 17 of 365 days2006: Unhealthy 1 of 365 days20062007: Good 227 of 365 days2007: Moderate 122 of 365 days2007: Unhealthy for Sensitive Groups 15 of 365 days2007: Unhealthy 1 of 365 days2008: Good 247 of 366 days2008: Moderate 111 of 366 days2008: Unhealthy for Sensitive Groups 8 of 366 days2009: Good 93 of 344 days2009: Moderate 248 of 344 days2009: Unhealthy for Sensitive Groups 3 of 344 days2010: Good 98 of 357 days2010: Moderate 249 of 357 days2010: Unhealthy for Sensitive Groups 9 of 357 days2010: Unhealthy 1 of 357 days2011: Good 126 of 365 days2011: Moderate 230 of 365 days2011: Unhealthy for Sensitive Groups 9 of 365 days20112012: Good 111 of 366 days2012: Moderate 240 of 366 days2012: Unhealthy for Sensitive Groups 13 of 366 days2012: Unhealthy 2 of 366 days2013: Good 123 of 365 days2013: Moderate 239 of 365 days2013: Unhealthy for Sensitive Groups 3 of 365 days2014: Good 161 of 365 days2014: Moderate 203 of 365 days2014: Unhealthy for Sensitive Groups 1 of 365 days2015: Good 168 of 365 days2015: Moderate 194 of 365 days2015: Unhealthy for Sensitive Groups 3 of 365 days2016: Good 148 of 366 days2016: Moderate 213 of 366 days2016: Unhealthy for Sensitive Groups 5 of 366 days20162017: Good 128 of 362 days2017: Moderate 234 of 362 days2018: Good 281 of 364 days2018: Moderate 81 of 364 days2018: Unhealthy for Sensitive Groups 2 of 364 days2019: Good 276 of 354 days2019: Moderate 78 of 354 days2020: Good 281 of 362 days2020: Moderate 81 of 362 days2021: Good 196 of 354 days2021: Moderate 157 of 354 days2021: Unhealthy for Sensitive Groups 1 of 354 days20212022: Good 198 of 304 days2022: Moderate 106 of 304 days2023: Good 227 of 298 days2023: Moderate 70 of 298 days2023: Unhealthy for Sensitive Groups 1 of 298 days2024: Good 278 of 363 days2024: Moderate 85 of 363 days2025: Good 283 of 362 days2025: Moderate 78 of 362 days2025: Unhealthy for Sensitive Groups 1 of 362 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 year0501001501980: 90th percentile AQI 451981: 90th percentile AQI 841982: 90th percentile AQI 231989: 90th percentile AQI 591990: 90th percentile AQI 801991: 90th percentile AQI 871992: 90th percentile AQI 421993: 90th percentile AQI 901994: 90th percentile AQI 931995: 90th percentile AQI 1011996: 90th percentile AQI 771997: 90th percentile AQI 611998: 90th percentile AQI 541999: 90th percentile AQI 1052000: 90th percentile AQI 772001: 90th percentile AQI 972002: 90th percentile AQI 932003: 90th percentile AQI 762004: 90th percentile AQI 742005: 90th percentile AQI 872006: 90th percentile AQI 802007: 90th percentile AQI 872008: 90th percentile AQI 722009: 90th percentile AQI 772010: 90th percentile AQI 802011: 90th percentile AQI 802012: 90th percentile AQI 772013: 90th percentile AQI 732014: 90th percentile AQI 672015: 90th percentile AQI 742016: 90th percentile AQI 692017: 90th percentile AQI 672018: 90th percentile AQI 572019: 90th percentile AQI 552020: 90th percentile AQI 552021: 90th percentile AQI 632022: 90th percentile AQI 582023: 90th percentile AQI 602024: 90th percentile AQI 562025: 90th percentile AQI 581980: Median AQI 321981: Median AQI 271982: Median AQI 171989: Median AQI 321990: Median AQI 321991: Median AQI 391992: Median AQI 281993: Median AQI 371994: Median AQI 361995: Median AQI 361996: Median AQI 361997: Median AQI 351998: Median AQI 341999: Median AQI 422000: Median AQI 392001: Median AQI 462002: Median AQI 442003: Median AQI 432004: Median AQI 422005: Median AQI 442006: Median AQI 412007: Median AQI 422008: Median AQI 412009: Median AQI 562010: Median AQI 582011: Median AQI 562012: Median AQI 552013: Median AQI 552014: Median AQI 522015: Median AQI 522016: Median AQI 532017: Median AQI 552018: Median AQI 402019: Median AQI 412020: Median AQI 392021: Median AQI 472022: Median AQI 412023: Median AQI 422024: Median AQI 392025: Median AQI 39198019911996200120062011201620212025
  • 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
Ozone23264%
Fine particles (PM2.5)13036%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253622837810003958126Ozone
2024363278850000395688PM2.5
20232982277010004260133Ozone
20223041981060000415876PM2.5
202135419615710004763124PM2.5
2020362281810000395583PM2.5
2019354276780000415593Ozone
20183642818120004057122Ozone
201736212823400005567100PM2.5
201636614821350005369112PM2.5
201536516819430005274147PM2.5
201436516120310005267105PM2.5
201336512323930005573129PM2.5
2012366111240132005577156PM2.5
201136512623090005680122PM2.5
20103579824991005880174PM2.5
20093449324830005677108PM2.5
200836624711180004172143Ozone
2007365227122151004287156Ozone
2006365241106171004180151Ozone
2005365214128185004487179Ozone
200436623812161004274155Ozone
200336522712863104376205Ozone
20023652151162310104493202Ozone
2001365203127332004697174Ozone
2000366244110102003977174Ozone
19993652279527142042105230Ozone
19983643213283003454159NO2
19972732313262203561203Ozone
19962321824181003677169Ozone
1995218162341561036101202Ozone
199419515424107003693187Ozone
199322716942115003790182Ozone
19922232121010002842112Ozone
199124217352143003987169Ozone
19902221862772003280172Ozone
19895240120000325980PM10
1982222200000172326Ozone
19811621361373302784208NO2
1980413830000324560NO2

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 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