EnviroNearby

Harford County, Maryland air quality history

Daily Air Quality Index summaries from EPA monitors in Harford, Maryland, 1980–2025.

76%
Good days in 2025
42
Median daily AQI, 2025
3
Days above 100 in 2025
343
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Harford, Maryland on 343 days. 259 of those days (76%) were in the Good range, and the median daily AQI was 42. That median is higher than the typical monitored county in Maryland (median 39.5 across 16 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 202 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 73% in 1980–1982 versus 71% 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 149 of 228 days1980: Moderate 31 of 228 days1980: Unhealthy for Sensitive Groups 22 of 228 days1980: Unhealthy 15 of 228 days1980: Very Unhealthy 11 of 228 days19801981: Good 263 of 324 days1981: Moderate 31 of 324 days1981: Unhealthy for Sensitive Groups 17 of 324 days1981: Unhealthy 9 of 324 days1981: Very Unhealthy 4 of 324 days1982: Good 238 of 328 days1982: Moderate 47 of 328 days1982: Unhealthy for Sensitive Groups 32 of 328 days1982: Unhealthy 7 of 328 days1982: Very Unhealthy 4 of 328 days1983: Good 233 of 335 days1983: Moderate 39 of 335 days1983: Unhealthy for Sensitive Groups 25 of 335 days1983: Unhealthy 25 of 335 days1983: Very Unhealthy 13 of 335 days1984: Good 279 of 362 days1984: Moderate 47 of 362 days1984: Unhealthy for Sensitive Groups 22 of 362 days1984: Unhealthy 13 of 362 days1984: Very Unhealthy 1 of 362 days1985: Good 248 of 335 days1985: Moderate 39 of 335 days1985: Unhealthy for Sensitive Groups 31 of 335 days1985: Unhealthy 14 of 335 days1985: Very Unhealthy 3 of 335 days19851986: Good 255 of 354 days1986: Moderate 46 of 354 days1986: Unhealthy for Sensitive Groups 24 of 354 days1986: Unhealthy 21 of 354 days1986: Very Unhealthy 8 of 354 days1987: Good 235 of 359 days1987: Moderate 54 of 359 days1987: Unhealthy for Sensitive Groups 34 of 359 days1987: Unhealthy 25 of 359 days1987: Very Unhealthy 11 of 359 days1988: Good 243 of 356 days1988: Moderate 45 of 356 days1988: Unhealthy for Sensitive Groups 25 of 356 days1988: Unhealthy 24 of 356 days1988: Very Unhealthy 19 of 356 days1989: Good 198 of 274 days1989: Moderate 35 of 274 days1989: Unhealthy for Sensitive Groups 27 of 274 days1989: Unhealthy 13 of 274 days1989: Very Unhealthy 1 of 274 days1990: Good 249 of 356 days1990: Moderate 57 of 356 days1990: Unhealthy for Sensitive Groups 35 of 356 days1990: Unhealthy 11 of 356 days1990: Very Unhealthy 4 of 356 days19901991: Good 211 of 333 days1991: Moderate 48 of 333 days1991: Unhealthy for Sensitive Groups 41 of 333 days1991: Unhealthy 26 of 333 days1991: Very Unhealthy 7 of 333 days1992: Good 269 of 366 days1992: Moderate 63 of 366 days1992: Unhealthy for Sensitive Groups 24 of 366 days1992: Unhealthy 9 of 366 days1992: Very Unhealthy 1 of 366 days1993: Good 236 of 352 days1993: Moderate 45 of 352 days1993: Unhealthy for Sensitive Groups 47 of 352 days1993: Unhealthy 16 of 352 days1993: Very Unhealthy 8 of 352 days1994: Good 252 of 359 days1994: Moderate 51 of 359 days1994: Unhealthy for Sensitive Groups 28 of 359 days1994: Unhealthy 23 of 359 days1994: Very Unhealthy 5 of 359 days1995: Good 244 of 360 days1995: Moderate 58 of 360 days1995: Unhealthy for Sensitive Groups 36 of 360 days1995: Unhealthy 15 of 360 days1995: Very Unhealthy 7 of 360 days19951996: Good 254 of 359 days1996: Moderate 59 of 359 days1996: Unhealthy for Sensitive Groups 38 of 359 days1996: Unhealthy 5 of 359 days1996: Very Unhealthy 3 of 359 days1997: Good 253 of 363 days1997: Moderate 59 of 363 days1997: Unhealthy for Sensitive Groups 27 of 363 days1997: Unhealthy 16 of 363 days1997: Very Unhealthy 8 of 363 days1998: Good 237 of 353 days1998: Moderate 59 of 353 days1998: Unhealthy for Sensitive Groups 37 of 353 days1998: Unhealthy 17 of 353 days1998: Very Unhealthy 3 of 353 days1999: Good 247 of 362 days1999: Moderate 67 of 362 days1999: Unhealthy for Sensitive Groups 29 of 362 days1999: Unhealthy 12 of 362 days1999: Very Unhealthy 7 of 362 days2000: Good 237 of 366 days2000: Moderate 103 of 366 days2000: Unhealthy for Sensitive Groups 14 of 366 days2000: Unhealthy 11 of 366 days2000: Very Unhealthy 1 of 366 days20002001: Good 214 of 365 days2001: Moderate 103 of 365 days2001: Unhealthy for Sensitive Groups 27 of 365 days2001: Unhealthy 16 of 365 days2001: Very Unhealthy 5 of 365 days2002: Good 219 of 363 days2002: Moderate 82 of 363 days2002: Unhealthy for Sensitive Groups 35 of 363 days2002: Unhealthy 17 of 363 days2002: Very Unhealthy 10 of 363 days2003: Good 203 of 323 days2003: Moderate 91 of 323 days2003: Unhealthy for Sensitive Groups 24 of 323 days2003: Unhealthy 3 of 323 days2003: Very Unhealthy 2 of 323 days2004: Good 129 of 261 days2004: Moderate 98 of 261 days2004: Unhealthy for Sensitive Groups 29 of 261 days2004: Unhealthy 5 of 261 days2005: Good 122 of 264 days2005: Moderate 107 of 264 days2005: Unhealthy for Sensitive Groups 21 of 264 days2005: Unhealthy 11 of 264 days2005: Very Unhealthy 3 of 264 days20052006: Good 132 of 262 days2006: Moderate 97 of 262 days2006: Unhealthy for Sensitive Groups 24 of 262 days2006: Unhealthy 9 of 262 days2007: Good 119 of 261 days2007: Moderate 98 of 261 days2007: Unhealthy for Sensitive Groups 33 of 261 days2007: Unhealthy 9 of 261 days2007: Very Unhealthy 2 of 261 days2008: Good 141 of 263 days2008: Moderate 93 of 263 days2008: Unhealthy for Sensitive Groups 21 of 263 days2008: Unhealthy 8 of 263 days2009: Good 155 of 262 days2009: Moderate 94 of 262 days2009: Unhealthy for Sensitive Groups 11 of 262 days2009: Unhealthy 1 of 262 days2009: Very Unhealthy 1 of 262 days2010: Good 133 of 263 days2010: Moderate 89 of 263 days2010: Unhealthy for Sensitive Groups 24 of 263 days2010: Unhealthy 16 of 263 days2010: Very Unhealthy 1 of 263 days20102011: Good 125 of 304 days2011: Moderate 150 of 304 days2011: Unhealthy for Sensitive Groups 17 of 304 days2011: Unhealthy 9 of 304 days2011: Very Unhealthy 3 of 304 days2012: Good 153 of 360 days2012: Moderate 185 of 360 days2012: Unhealthy for Sensitive Groups 17 of 360 days2012: Unhealthy 4 of 360 days2012: Very Unhealthy 1 of 360 days2013: Good 180 of 353 days2013: Moderate 168 of 353 days2013: Unhealthy for Sensitive Groups 5 of 353 days2014: Good 161 of 357 days2014: Moderate 193 of 357 days2014: Unhealthy for Sensitive Groups 3 of 357 days2015: Good 198 of 358 days2015: Moderate 154 of 358 days2015: Unhealthy for Sensitive Groups 5 of 358 days2015: Unhealthy 1 of 358 days20152016: Good 211 of 359 days2016: Moderate 136 of 359 days2016: Unhealthy for Sensitive Groups 11 of 359 days2016: Unhealthy 1 of 359 days2017: Good 206 of 358 days2017: Moderate 143 of 358 days2017: Unhealthy for Sensitive Groups 7 of 358 days2017: Unhealthy 2 of 358 days2018: Good 247 of 358 days2018: Moderate 101 of 358 days2018: Unhealthy for Sensitive Groups 10 of 358 days2019: Good 229 of 359 days2019: Moderate 121 of 359 days2019: Unhealthy for Sensitive Groups 9 of 359 days2020: Good 286 of 357 days2020: Moderate 70 of 357 days2020: Unhealthy for Sensitive Groups 1 of 357 days20202021: Good 219 of 357 days2021: Moderate 129 of 357 days2021: Unhealthy for Sensitive Groups 9 of 357 days2022: Good 262 of 360 days2022: Moderate 98 of 360 days2023: Good 238 of 359 days2023: Moderate 111 of 359 days2023: Unhealthy for Sensitive Groups 7 of 359 days2023: Unhealthy 3 of 359 days2024: Good 262 of 363 days2024: Moderate 95 of 363 days2024: Unhealthy for Sensitive Groups 5 of 363 days2024: Unhealthy 1 of 363 days2025: Good 259 of 343 days2025: Moderate 81 of 343 days2025: Unhealthy for Sensitive Groups 3 of 343 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 1611981: 90th percentile AQI 971982: 90th percentile AQI 1191983: 90th percentile AQI 1591984: 90th percentile AQI 1001985: 90th percentile AQI 1191986: 90th percentile AQI 1331987: 90th percentile AQI 1511988: 90th percentile AQI 1661989: 90th percentile AQI 1221990: 90th percentile AQI 1221991: 90th percentile AQI 1471992: 90th percentile AQI 1001993: 90th percentile AQI 1331994: 90th percentile AQI 1361995: 90th percentile AQI 1261996: 90th percentile AQI 1151997: 90th percentile AQI 1221998: 90th percentile AQI 1361999: 90th percentile AQI 1122000: 90th percentile AQI 902001: 90th percentile AQI 1192002: 90th percentile AQI 1362003: 90th percentile AQI 972004: 90th percentile AQI 1082005: 90th percentile AQI 1122006: 90th percentile AQI 1122007: 90th percentile AQI 1192008: 90th percentile AQI 1012009: 90th percentile AQI 902010: 90th percentile AQI 1192011: 90th percentile AQI 1002012: 90th percentile AQI 832013: 90th percentile AQI 742014: 90th percentile AQI 692015: 90th percentile AQI 732016: 90th percentile AQI 742017: 90th percentile AQI 642018: 90th percentile AQI 662019: 90th percentile AQI 712020: 90th percentile AQI 582021: 90th percentile AQI 712022: 90th percentile AQI 642023: 90th percentile AQI 742024: 90th percentile AQI 642025: 90th percentile AQI 611980: Median AQI 391981: Median AQI 271982: Median AQI 361983: Median AQI 361984: Median AQI 351985: Median AQI 291986: Median AQI 311987: Median AQI 381988: Median AQI 381989: Median AQI 311990: Median AQI 351991: Median AQI 391992: Median AQI 351993: Median AQI 371994: Median AQI 381995: Median AQI 391996: Median AQI 371997: Median AQI 391998: Median AQI 391999: Median AQI 402000: Median AQI 392001: Median AQI 472002: Median AQI 442003: Median AQI 432004: Median AQI 512005: Median AQI 532006: Median AQI 502007: Median AQI 532008: Median AQI 492009: Median AQI 462010: Median AQI 502011: Median AQI 542012: Median AQI 542013: Median AQI 502014: Median AQI 522015: Median AQI 482016: Median AQI 482017: Median AQI 472018: Median AQI 422019: Median AQI 452020: Median AQI 412021: Median AQI 462022: Median AQI 432023: Median AQI 452024: Median AQI 422025: Median AQI 421980198519901995200020052010201520202025
  • 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
Ozone20259%
Fine particles (PM2.5)14141%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253432598130004261143Ozone
20243632629551004264154Ozone
202335923811173004574200Ozone
2022360262980000436497Ozone
202135721912990004671122PM2.5
20203572867010004158119Ozone
201935922912190004571133Ozone
2018358247101100004266150PM2.5
201735820614372004764156PM2.5
2016359211136111004874154PM2.5
201535819815451004873156PM2.5
201435716119330005269133PM2.5
201335318016850005074133PM2.5
2012360153185174105483201PM2.5
20113041251501793054100209Ozone
20102631338924161050119205Ozone
200926215594111104690204Ozone
2008263141932180049101192Ozone
2007261119983392053119208Ozone
2006262132972490050112195Ozone
200526412210721113053112204Ozone
2004261129982950051108190Ozone
200332320391243204397226Ozone
200236321982351710044136224Ozone
200136521410327165047119225Ozone
20003662371031411103990212Ozone
19993622476729127040112221Ozone
19983532375937173039136213Ozone
19973632535927168039122235Ozone
1996359254593853037115205Ozone
19953602445836157039126228Ozone
19943592525128235038136215Ozone
19933522364547168037133230Ozone
1992366269632491035100206Ozone
19913332114841267039147227Ozone
19903562495735114035122225Ozone
19892741983527131031122239Ozone
198835624345252419038166253Ozone
198735923554342511038151248Ozone
19863542554624218031133227Ozone
19853352483931143029119244Ozone
19843622794722131035100206Ozone
198333523339252513036159261Ozone
1982328238473274036119218Ozone
198132426331179402797218Ozone
198022814931221511039161234Ozone

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 Maryland with a similar median AQI in 2025

All monitored counties in Maryland

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