EnviroNearby

Montgomery County, Pennsylvania air quality history

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

73%
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 Montgomery, Pennsylvania on 365 days. 268 of those days (73%) 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 219 days. Across the years with fuller monitoring, the share of Good days rose: an average of 58% in 1980–1982 versus 70% 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 180 of 351 days1980: Moderate 92 of 351 days1980: Unhealthy for Sensitive Groups 28 of 351 days1980: Unhealthy 18 of 351 days1980: Very Unhealthy 33 of 351 days19801981: Good 226 of 345 days1981: Moderate 86 of 345 days1981: Unhealthy for Sensitive Groups 19 of 345 days1981: Unhealthy 7 of 345 days1981: Very Unhealthy 7 of 345 days1982: Good 209 of 362 days1982: Moderate 125 of 362 days1982: Unhealthy for Sensitive Groups 20 of 362 days1982: Unhealthy 7 of 362 days1982: Very Unhealthy 1 of 362 days1983: Good 242 of 359 days1983: Moderate 80 of 359 days1983: Unhealthy for Sensitive Groups 23 of 359 days1983: Unhealthy 13 of 359 days1983: Very Unhealthy 1 of 359 days1984: Good 223 of 359 days1984: Moderate 118 of 359 days1984: Unhealthy for Sensitive Groups 14 of 359 days1984: Unhealthy 3 of 359 days1984: Very Unhealthy 1 of 359 days1985: Good 250 of 364 days1985: Moderate 79 of 364 days1985: Unhealthy for Sensitive Groups 25 of 364 days1985: Unhealthy 7 of 364 days1985: Very Unhealthy 3 of 364 days19851986: Good 291 of 364 days1986: Moderate 41 of 364 days1986: Unhealthy for Sensitive Groups 19 of 364 days1986: Unhealthy 13 of 364 days1987: Good 279 of 360 days1987: Moderate 37 of 360 days1987: Unhealthy for Sensitive Groups 22 of 360 days1987: Unhealthy 13 of 360 days1987: Very Unhealthy 9 of 360 days1988: Good 275 of 358 days1988: Moderate 29 of 358 days1988: Unhealthy for Sensitive Groups 21 of 358 days1988: Unhealthy 16 of 358 days1988: Very Unhealthy 17 of 358 days1989: Good 294 of 362 days1989: Moderate 43 of 362 days1989: Unhealthy for Sensitive Groups 17 of 362 days1989: Unhealthy 7 of 362 days1989: Very Unhealthy 1 of 362 days1990: Good 297 of 364 days1990: Moderate 45 of 364 days1990: Unhealthy for Sensitive Groups 16 of 364 days1990: Unhealthy 5 of 364 days1990: Very Unhealthy 1 of 364 days19901991: Good 260 of 364 days1991: Moderate 59 of 364 days1991: Unhealthy for Sensitive Groups 32 of 364 days1991: Unhealthy 12 of 364 days1991: Very Unhealthy 1 of 364 days1992: Good 287 of 366 days1992: Moderate 54 of 366 days1992: Unhealthy for Sensitive Groups 19 of 366 days1992: Unhealthy 5 of 366 days1992: Very Unhealthy 1 of 366 days1993: Good 243 of 365 days1993: Moderate 76 of 365 days1993: Unhealthy for Sensitive Groups 33 of 365 days1993: Unhealthy 12 of 365 days1993: Very Unhealthy 1 of 365 days1994: Good 219 of 364 days1994: Moderate 110 of 364 days1994: Unhealthy for Sensitive Groups 26 of 364 days1994: Unhealthy 9 of 364 days1995: Good 208 of 308 days1995: Moderate 69 of 308 days1995: Unhealthy for Sensitive Groups 19 of 308 days1995: Unhealthy 11 of 308 days1995: Very Unhealthy 1 of 308 days19951996: Good 268 of 365 days1996: Moderate 64 of 365 days1996: Unhealthy for Sensitive Groups 25 of 365 days1996: Unhealthy 8 of 365 days1997: Good 258 of 361 days1997: Moderate 70 of 361 days1997: Unhealthy for Sensitive Groups 14 of 361 days1997: Unhealthy 14 of 361 days1997: Very Unhealthy 5 of 361 days1998: Good 247 of 365 days1998: Moderate 64 of 365 days1998: Unhealthy for Sensitive Groups 38 of 365 days1998: Unhealthy 14 of 365 days1998: Very Unhealthy 2 of 365 days1999: Good 245 of 365 days1999: Moderate 79 of 365 days1999: Unhealthy for Sensitive Groups 22 of 365 days1999: Unhealthy 16 of 365 days1999: Very Unhealthy 3 of 365 days2000: Good 217 of 363 days2000: Moderate 116 of 363 days2000: Unhealthy for Sensitive Groups 19 of 363 days2000: Unhealthy 9 of 363 days2000: Very Unhealthy 2 of 363 days20002001: Good 213 of 365 days2001: Moderate 114 of 365 days2001: Unhealthy for Sensitive Groups 22 of 365 days2001: Unhealthy 13 of 365 days2001: Very Unhealthy 3 of 365 days2002: Good 226 of 365 days2002: Moderate 94 of 365 days2002: Unhealthy for Sensitive Groups 30 of 365 days2002: Unhealthy 15 of 365 days2003: Good 254 of 365 days2003: Moderate 97 of 365 days2003: Unhealthy for Sensitive Groups 11 of 365 days2003: Unhealthy 2 of 365 days2003: Very Unhealthy 1 of 365 days2004: Good 254 of 366 days2004: Moderate 100 of 366 days2004: Unhealthy for Sensitive Groups 12 of 366 days2005: Good 244 of 365 days2005: Moderate 90 of 365 days2005: Unhealthy for Sensitive Groups 24 of 365 days2005: Unhealthy 7 of 365 days20052006: Good 247 of 365 days2006: Moderate 90 of 365 days2006: Unhealthy for Sensitive Groups 25 of 365 days2006: Unhealthy 3 of 365 days2007: Good 237 of 365 days2007: Moderate 103 of 365 days2007: Unhealthy for Sensitive Groups 22 of 365 days2007: Unhealthy 3 of 365 days2008: Good 244 of 366 days2008: Moderate 98 of 366 days2008: Unhealthy for Sensitive Groups 22 of 366 days2008: Unhealthy 2 of 366 days2009: Good 168 of 342 days2009: Moderate 171 of 342 days2009: Unhealthy for Sensitive Groups 3 of 342 days2010: Good 165 of 346 days2010: Moderate 163 of 346 days2010: Unhealthy for Sensitive Groups 17 of 346 days2010: Unhealthy 1 of 346 days20102011: Good 147 of 365 days2011: Moderate 202 of 365 days2011: Unhealthy for Sensitive Groups 15 of 365 days2011: Unhealthy 1 of 365 days2012: Good 178 of 366 days2012: Moderate 180 of 366 days2012: Unhealthy for Sensitive Groups 8 of 366 days2013: Good 201 of 365 days2013: Moderate 158 of 365 days2013: Unhealthy for Sensitive Groups 6 of 365 days2014: Good 210 of 365 days2014: Moderate 149 of 365 days2014: Unhealthy for Sensitive Groups 6 of 365 days2015: Good 206 of 365 days2015: Moderate 153 of 365 days2015: Unhealthy for Sensitive Groups 6 of 365 days20152016: Good 266 of 317 days2016: Moderate 46 of 317 days2016: Unhealthy for Sensitive Groups 5 of 317 days2017: Good 210 of 364 days2017: Moderate 147 of 364 days2017: Unhealthy for Sensitive Groups 7 of 364 days2018: Good 242 of 352 days2018: Moderate 103 of 352 days2018: Unhealthy for Sensitive Groups 7 of 352 days2019: Good 262 of 362 days2019: Moderate 99 of 362 days2019: Unhealthy for Sensitive Groups 1 of 362 days2020: Good 269 of 366 days2020: Moderate 97 of 366 days20202021: Good 202 of 356 days2021: Moderate 148 of 356 days2021: Unhealthy for Sensitive Groups 6 of 356 days2022: Good 237 of 362 days2022: Moderate 124 of 362 days2022: Unhealthy for Sensitive Groups 1 of 362 days2023: Good 232 of 365 days2023: Moderate 127 of 365 days2023: Unhealthy for Sensitive Groups 1 of 365 days2023: Unhealthy 3 of 365 days2023: Very Unhealthy 2 of 365 days2024: Good 266 of 365 days2024: Moderate 98 of 365 days2024: Unhealthy for Sensitive Groups 1 of 365 days2025: Good 268 of 365 days2025: Moderate 96 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 year0501001502001980: 90th percentile AQI 1921981: 90th percentile AQI 971982: 90th percentile AQI 941983: 90th percentile AQI 1051984: 90th percentile AQI 841985: 90th percentile AQI 1001986: 90th percentile AQI 931987: 90th percentile AQI 1191988: 90th percentile AQI 1471989: 90th percentile AQI 741990: 90th percentile AQI 771991: 90th percentile AQI 1081992: 90th percentile AQI 801993: 90th percentile AQI 1151994: 90th percentile AQI 1001995: 90th percentile AQI 1011996: 90th percentile AQI 901997: 90th percentile AQI 901998: 90th percentile AQI 1261999: 90th percentile AQI 1082000: 90th percentile AQI 902001: 90th percentile AQI 1012002: 90th percentile AQI 1122003: 90th percentile AQI 802004: 90th percentile AQI 772005: 90th percentile AQI 902006: 90th percentile AQI 902007: 90th percentile AQI 902008: 90th percentile AQI 872009: 90th percentile AQI 742010: 90th percentile AQI 872011: 90th percentile AQI 802012: 90th percentile AQI 742013: 90th percentile AQI 712014: 90th percentile AQI 682015: 90th percentile AQI 732016: 90th percentile AQI 612017: 90th percentile AQI 682018: 90th percentile AQI 672019: 90th percentile AQI 612020: 90th percentile AQI 602021: 90th percentile AQI 672022: 90th percentile AQI 612023: 90th percentile AQI 672024: 90th percentile AQI 612025: 90th percentile AQI 611980: Median AQI 501981: Median AQI 421982: Median AQI 471983: Median AQI 431984: Median AQI 441985: Median AQI 411986: Median AQI 321987: Median AQI 311988: Median AQI 311989: Median AQI 311990: Median AQI 311991: Median AQI 391992: Median AQI 381993: Median AQI 431994: Median AQI 471995: Median AQI 431996: Median AQI 411997: Median AQI 421998: Median AQI 431999: Median AQI 402000: Median AQI 432001: Median AQI 452002: Median AQI 422003: Median AQI 412004: Median AQI 402005: Median AQI 432006: Median AQI 422007: Median AQI 412008: Median AQI 422009: Median AQI 512010: Median AQI 522011: Median AQI 542012: Median AQI 512013: Median AQI 482014: Median AQI 472015: Median AQI 472016: Median AQI 342017: Median AQI 472018: Median AQI 412019: Median AQI 402020: Median AQI 432021: Median AQI 472022: Median AQI 442023: Median AQI 442024: Median AQI 402025: Median AQI 411980198519901995200020052010201520202025
  • 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
Ozone21960%
Fine particles (PM2.5)14640%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652689610004161133Ozone
20243652669810004061140Ozone
202336523212713204467284PM2.5
202236223712410004461108PM2.5
202135620214860004767150PM2.5
2020366269970000436099PM2.5
20193622629910004061129PM2.5
201835224210370004167129PM2.5
201736421014770004768129PM2.5
20163172664650003461140Ozone
201536520615360004773133Ozone
201436521014960004768122PM2.5
201336520115860004871115PM2.5
201236617818080005174126PM2.5
2011365147202151005480151PM2.5
2010346165163171005287159PM2.5
200934216817130005174115PM2.5
200836624498222004287177Ozone
2007365237103223004190164Ozone
200636524790253004290159Ozone
200536524490247004390169Ozone
2004366254100120004077150Ozone
200336525497112104180202Ozone
20023652269430150042112195Ozone
200136521311422133045101206Ozone
2000363217116199204390228NO2
19993652457922163040108210NO2
19983652476438142043126204NO2
1997361258701414504290215NO2
199636526864258004190187NO2
19953082086919111043101209Ozone
19943642191102690047100179NO2
19933652437633121043115216NO2
199236628754195103880201Ozone
19913642605932121039108214Ozone
199036429745165103177207Ozone
198936229443177103174201Ozone
198835827529211617031147226Ozone
19873602793722139031119215Ozone
1986364291411913003293195Ozone
1985364250792573041100228Ozone
1984359223118143104484222NO2
19833592428023131043105218NO2
1982362209125207104794210NO2
198134522686197704297267Ozone
198035118092281833050192244Ozone

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