EnviroNearby

Delaware County, Pennsylvania air quality history

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

65%
Good days in 2025
44
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 Delaware, Pennsylvania on 365 days. 238 of those days (65%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Pennsylvania (median 40 across 38 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 211 days. Across the years with fuller monitoring, the share of Good days rose: an average of 55% in 1980–1982 versus 62% 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 162 of 342 days1980: Moderate 94 of 342 days1980: Unhealthy for Sensitive Groups 31 of 342 days1980: Unhealthy 29 of 342 days1980: Very Unhealthy 26 of 342 days19801981: Good 200 of 359 days1981: Moderate 107 of 359 days1981: Unhealthy for Sensitive Groups 29 of 359 days1981: Unhealthy 20 of 359 days1981: Very Unhealthy 3 of 359 days1982: Good 227 of 364 days1982: Moderate 91 of 364 days1982: Unhealthy for Sensitive Groups 20 of 364 days1982: Unhealthy 20 of 364 days1982: Very Unhealthy 6 of 364 days1983: Good 220 of 365 days1983: Moderate 86 of 365 days1983: Unhealthy for Sensitive Groups 25 of 365 days1983: Unhealthy 25 of 365 days1983: Very Unhealthy 9 of 365 days1984: Good 222 of 364 days1984: Moderate 106 of 364 days1984: Unhealthy for Sensitive Groups 19 of 364 days1984: Unhealthy 12 of 364 days1984: Very Unhealthy 5 of 364 days1985: Good 237 of 362 days1985: Moderate 76 of 362 days1985: Unhealthy for Sensitive Groups 30 of 362 days1985: Unhealthy 18 of 362 days1985: Very Unhealthy 1 of 362 days19851986: Good 272 of 365 days1986: Moderate 51 of 365 days1986: Unhealthy for Sensitive Groups 22 of 365 days1986: Unhealthy 16 of 365 days1986: Very Unhealthy 4 of 365 days1987: Good 268 of 364 days1987: Moderate 37 of 364 days1987: Unhealthy for Sensitive Groups 32 of 364 days1987: Unhealthy 21 of 364 days1987: Very Unhealthy 6 of 364 days1988: Good 266 of 358 days1988: Moderate 34 of 358 days1988: Unhealthy for Sensitive Groups 20 of 358 days1988: Unhealthy 18 of 358 days1988: Very Unhealthy 20 of 358 days1989: Good 285 of 365 days1989: Moderate 40 of 365 days1989: Unhealthy for Sensitive Groups 23 of 365 days1989: Unhealthy 17 of 365 days1990: Good 281 of 364 days1990: Moderate 47 of 364 days1990: Unhealthy for Sensitive Groups 26 of 364 days1990: Unhealthy 7 of 364 days1990: Very Unhealthy 3 of 364 days19901991: Good 244 of 363 days1991: Moderate 70 of 363 days1991: Unhealthy for Sensitive Groups 32 of 363 days1991: Unhealthy 15 of 363 days1991: Very Unhealthy 2 of 363 days1992: Good 282 of 362 days1992: Moderate 59 of 362 days1992: Unhealthy for Sensitive Groups 17 of 362 days1992: Unhealthy 4 of 362 days1993: Good 243 of 364 days1993: Moderate 75 of 364 days1993: Unhealthy for Sensitive Groups 31 of 364 days1993: Unhealthy 15 of 364 days1994: Good 239 of 363 days1994: Moderate 86 of 363 days1994: Unhealthy for Sensitive Groups 32 of 363 days1994: Unhealthy 6 of 363 days1995: Good 254 of 356 days1995: Moderate 69 of 356 days1995: Unhealthy for Sensitive Groups 19 of 356 days1995: Unhealthy 10 of 356 days1995: Very Unhealthy 4 of 356 days19951996: Good 238 of 365 days1996: Moderate 96 of 365 days1996: Unhealthy for Sensitive Groups 24 of 365 days1996: Unhealthy 7 of 365 days1997: Good 262 of 364 days1997: Moderate 62 of 364 days1997: Unhealthy for Sensitive Groups 23 of 364 days1997: Unhealthy 15 of 364 days1997: Very Unhealthy 2 of 364 days1998: Good 241 of 355 days1998: Moderate 67 of 355 days1998: Unhealthy for Sensitive Groups 32 of 355 days1998: Unhealthy 14 of 355 days1998: Very Unhealthy 1 of 355 days1999: Good 226 of 360 days1999: Moderate 97 of 360 days1999: Unhealthy for Sensitive Groups 18 of 360 days1999: Unhealthy 17 of 360 days1999: Very Unhealthy 2 of 360 days2000: Good 221 of 364 days2000: Moderate 123 of 364 days2000: Unhealthy for Sensitive Groups 14 of 364 days2000: Unhealthy 5 of 364 days2000: Very Unhealthy 1 of 364 days20002001: Good 214 of 365 days2001: Moderate 124 of 365 days2001: Unhealthy for Sensitive Groups 17 of 365 days2001: Unhealthy 10 of 365 days2002: Good 208 of 365 days2002: Moderate 109 of 365 days2002: Unhealthy for Sensitive Groups 29 of 365 days2002: Unhealthy 15 of 365 days2002: Very Unhealthy 4 of 365 days2003: Good 216 of 364 days2003: Moderate 120 of 364 days2003: Unhealthy for Sensitive Groups 25 of 364 days2003: Unhealthy 1 of 364 days2003: Very Unhealthy 2 of 364 days2004: Good 232 of 366 days2004: Moderate 117 of 366 days2004: Unhealthy for Sensitive Groups 15 of 366 days2004: Unhealthy 2 of 366 days2005: Good 210 of 363 days2005: Moderate 123 of 363 days2005: Unhealthy for Sensitive Groups 25 of 363 days2005: Unhealthy 5 of 363 days20052006: Good 230 of 365 days2006: Moderate 109 of 365 days2006: Unhealthy for Sensitive Groups 23 of 365 days2006: Unhealthy 3 of 365 days2007: Good 223 of 365 days2007: Moderate 121 of 365 days2007: Unhealthy for Sensitive Groups 17 of 365 days2007: Unhealthy 3 of 365 days2007: Very Unhealthy 1 of 365 days2008: Good 231 of 366 days2008: Moderate 118 of 366 days2008: Unhealthy for Sensitive Groups 15 of 366 days2008: Unhealthy 2 of 366 days2009: Good 121 of 363 days2009: Moderate 236 of 363 days2009: Unhealthy for Sensitive Groups 6 of 363 days2010: Good 132 of 365 days2010: Moderate 224 of 365 days2010: Unhealthy for Sensitive Groups 8 of 365 days2010: Unhealthy 1 of 365 days20102011: Good 122 of 363 days2011: Moderate 227 of 363 days2011: Unhealthy for Sensitive Groups 13 of 363 days2011: Unhealthy 1 of 363 days2012: Good 139 of 365 days2012: Moderate 204 of 365 days2012: Unhealthy for Sensitive Groups 21 of 365 days2012: Unhealthy 1 of 365 days2013: Good 139 of 365 days2013: Moderate 221 of 365 days2013: Unhealthy for Sensitive Groups 5 of 365 days2014: Good 95 of 361 days2014: Moderate 262 of 361 days2014: Unhealthy for Sensitive Groups 4 of 361 days2015: Good 120 of 365 days2015: Moderate 236 of 365 days2015: Unhealthy for Sensitive Groups 9 of 365 days20152016: Good 121 of 366 days2016: Moderate 240 of 366 days2016: Unhealthy for Sensitive Groups 5 of 366 days2017: Good 158 of 365 days2017: Moderate 205 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2018: Good 95 of 365 days2018: Moderate 264 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2019: Good 180 of 365 days2019: Moderate 178 of 365 days2019: Unhealthy for Sensitive Groups 7 of 365 days2020: Good 174 of 366 days2020: Moderate 189 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days20202021: Good 182 of 365 days2021: Moderate 180 of 365 days2021: Unhealthy for Sensitive Groups 3 of 365 days2022: Good 191 of 365 days2022: Moderate 174 of 365 days2023: Good 187 of 365 days2023: Moderate 169 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2023: Unhealthy 2 of 365 days2023: Very Unhealthy 2 of 365 days2024: Good 250 of 366 days2024: Moderate 114 of 366 days2024: Unhealthy for Sensitive Groups 2 of 366 days2025: Good 238 of 365 days2025: Moderate 124 of 365 days2025: Unhealthy for Sensitive Groups 2 of 365 days2025: Unhealthy 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 1821981: 90th percentile AQI 1121982: 90th percentile AQI 1121983: 90th percentile AQI 1471984: 90th percentile AQI 971985: 90th percentile AQI 1191986: 90th percentile AQI 1121987: 90th percentile AQI 1401988: 90th percentile AQI 1561989: 90th percentile AQI 1081990: 90th percentile AQI 1001991: 90th percentile AQI 1081992: 90th percentile AQI 801993: 90th percentile AQI 1121994: 90th percentile AQI 1011995: 90th percentile AQI 1001996: 90th percentile AQI 901997: 90th percentile AQI 1051998: 90th percentile AQI 1221999: 90th percentile AQI 1052000: 90th percentile AQI 832001: 90th percentile AQI 912002: 90th percentile AQI 1152003: 90th percentile AQI 902004: 90th percentile AQI 842005: 90th percentile AQI 932006: 90th percentile AQI 972007: 90th percentile AQI 872008: 90th percentile AQI 782009: 90th percentile AQI 742010: 90th percentile AQI 852011: 90th percentile AQI 792012: 90th percentile AQI 852013: 90th percentile AQI 752014: 90th percentile AQI 712015: 90th percentile AQI 742016: 90th percentile AQI 752017: 90th percentile AQI 702018: 90th percentile AQI 762019: 90th percentile AQI 742020: 90th percentile AQI 672021: 90th percentile AQI 672022: 90th percentile AQI 642023: 90th percentile AQI 742024: 90th percentile AQI 642025: 90th percentile AQI 651980: Median AQI 521981: Median AQI 471982: Median AQI 451983: Median AQI 451984: Median AQI 451985: Median AQI 431986: Median AQI 321987: Median AQI 321988: Median AQI 321989: Median AQI 311990: Median AQI 311991: Median AQI 421992: Median AQI 401993: Median AQI 431994: Median AQI 441995: Median AQI 411996: Median AQI 441997: Median AQI 421998: Median AQI 421999: Median AQI 442000: Median AQI 452001: Median AQI 472002: Median AQI 462003: Median AQI 442004: Median AQI 442005: Median AQI 452006: Median AQI 442007: Median AQI 442008: Median AQI 432009: Median AQI 562010: Median AQI 562011: Median AQI 562012: Median AQI 552013: Median AQI 542014: Median AQI 562015: Median AQI 552016: Median AQI 552017: Median AQI 522018: Median AQI 562019: Median AQI 512020: Median AQI 522021: Median AQI 512022: Median AQI 492023: Median AQI 502024: Median AQI 432025: Median AQI 441980198519901995200020052010201520202025
  • 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
Fine particles (PM2.5)21158%
Ozone15041%
Nitrogen dioxide (NO₂)41%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536523812421004465153PM2.5
202436625011420004364136PM2.5
202336518716952205074271PM2.5
20223651911740000496495PM2.5
202136518218030005167142PM2.5
202036617418930005267129PM2.5
201936518017870005174133PM2.5
20183659526460005676143PM2.5
201736515820520005270119PM2.5
201636612124050005575136PM2.5
201536512023690005574150PM2.5
20143619526240005671143PM2.5
201336513922150005475119PM2.5
2012365139204211005585154PM2.5
2011363122227131005679151PM2.5
201036513222481005685151PM2.5
200936312123660005674106PM2.5
2008366231118152004378166Ozone
2007365223121173104487202Ozone
2006365230109233004497166Ozone
2005363210123255004593161Ozone
2004366232117152004484161NO2
2003364216120251204490203NO2
200236520810929154046115218NO2
20013652141241710004791182Ozone
2000364221123145104583206NO2
19993602269718172044105213NO2
19983552416732141042122202NO2
19973642626223152042105214NO2
199636523896247004490179NO2
19953562546919104041100206NO2
1994363239863260044101200NO2
19933642437531150043112200NO2
199236228259174004080179NO2
19913632447032152042108208NO2
1990364281472673031100216Ozone
19893652854023170031108200Ozone
198835826634201820032156251Ozone
19873642683732216032140216Ozone
19863652725122164032112215Ozone
19853622377630181043119224Ozone
19843642221061912504597215NO2
19833652208625259045147239NO2
19823642279120206045112222NO2
198135920010729203047112241NO2
198034216294312926052182299Ozone

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