EnviroNearby

Dorchester County, Maryland air quality history

Daily Air Quality Index summaries from EPA monitors in Dorchester, Maryland, 1995–2025.

86%
Good days in 2025
39
Median daily AQI, 2025
0
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 Dorchester, Maryland on 365 days. 314 of those days (86%) were in the Good range, and the median daily AQI was 39. That median is about the same as 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 283 days. Across the years with fuller monitoring, the share of Good days rose: an average of 64% in 1996–1998 versus 80% in 2023–2025.

Years with fewer than 120 monitored days (1995) 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%1995: Good 9 of 54 days1995: Moderate 14 of 54 days1995: Unhealthy for Sensitive Groups 17 of 54 days1995: Unhealthy 14 of 54 days19951996: Good 131 of 212 days1996: Moderate 45 of 212 days1996: Unhealthy for Sensitive Groups 27 of 212 days1996: Unhealthy 9 of 212 days1997: Good 246 of 363 days1997: Moderate 57 of 363 days1997: Unhealthy for Sensitive Groups 36 of 363 days1997: Unhealthy 22 of 363 days1997: Very Unhealthy 2 of 363 days1998: Good 222 of 361 days1998: Moderate 79 of 361 days1998: Unhealthy for Sensitive Groups 30 of 361 days1998: Unhealthy 29 of 361 days1998: Very Unhealthy 1 of 361 days1999: Good 246 of 364 days1999: Moderate 69 of 364 days1999: Unhealthy for Sensitive Groups 25 of 364 days1999: Unhealthy 22 of 364 days1999: Very Unhealthy 2 of 364 days2000: Good 260 of 362 days2000: Moderate 60 of 362 days2000: Unhealthy for Sensitive Groups 34 of 362 days2000: Unhealthy 8 of 362 days20002001: Good 257 of 364 days2001: Moderate 66 of 364 days2001: Unhealthy for Sensitive Groups 32 of 364 days2001: Unhealthy 8 of 364 days2001: Very Unhealthy 1 of 364 days2002: Good 243 of 362 days2002: Moderate 72 of 362 days2002: Unhealthy for Sensitive Groups 30 of 362 days2002: Unhealthy 15 of 362 days2002: Very Unhealthy 2 of 362 days2003: Good 270 of 347 days2003: Moderate 51 of 347 days2003: Unhealthy for Sensitive Groups 19 of 347 days2003: Unhealthy 4 of 347 days2003: Very Unhealthy 3 of 347 days2004: Good 277 of 363 days2004: Moderate 61 of 363 days2004: Unhealthy for Sensitive Groups 23 of 363 days2004: Unhealthy 2 of 363 days2005: Good 269 of 356 days2005: Moderate 60 of 356 days2005: Unhealthy for Sensitive Groups 23 of 356 days2005: Unhealthy 4 of 356 days20052006: Good 259 of 363 days2006: Moderate 77 of 363 days2006: Unhealthy for Sensitive Groups 26 of 363 days2006: Unhealthy 1 of 363 days2007: Good 249 of 344 days2007: Moderate 65 of 344 days2007: Unhealthy for Sensitive Groups 29 of 344 days2007: Unhealthy 1 of 344 days2008: Good 273 of 363 days2008: Moderate 68 of 363 days2008: Unhealthy for Sensitive Groups 22 of 363 days2009: Good 315 of 361 days2009: Moderate 42 of 361 days2009: Unhealthy for Sensitive Groups 4 of 361 days2010: Good 272 of 355 days2010: Moderate 74 of 355 days2010: Unhealthy for Sensitive Groups 8 of 355 days2010: Unhealthy 1 of 355 days20102011: Good 246 of 318 days2011: Moderate 52 of 318 days2011: Unhealthy for Sensitive Groups 19 of 318 days2011: Unhealthy 1 of 318 days2012: Good 253 of 365 days2012: Moderate 94 of 365 days2012: Unhealthy for Sensitive Groups 14 of 365 days2012: Unhealthy 3 of 365 days2012: Very Unhealthy 1 of 365 days2013: Good 258 of 365 days2013: Moderate 105 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 218 of 365 days2014: Moderate 147 of 365 days2015: Good 233 of 365 days2015: Moderate 131 of 365 days2015: Unhealthy for Sensitive Groups 1 of 365 days20152016: Good 236 of 366 days2016: Moderate 127 of 366 days2016: Unhealthy for Sensitive Groups 3 of 366 days2017: Good 212 of 365 days2017: Moderate 153 of 365 days2018: Good 283 of 365 days2018: Moderate 80 of 365 days2018: Unhealthy for Sensitive Groups 1 of 365 days2018: Unhealthy 1 of 365 days2019: Good 281 of 365 days2019: Moderate 81 of 365 days2019: Unhealthy for Sensitive Groups 3 of 365 days2020: Good 339 of 365 days2020: Moderate 26 of 365 days20202021: Good 287 of 365 days2021: Moderate 77 of 365 days2021: Unhealthy for Sensitive Groups 1 of 365 days2022: Good 274 of 365 days2022: Moderate 91 of 365 days2023: Good 268 of 365 days2023: Moderate 90 of 365 days2023: Unhealthy for Sensitive Groups 4 of 365 days2023: Unhealthy 3 of 365 days2024: Good 294 of 366 days2024: Moderate 71 of 366 days2024: Unhealthy for Sensitive Groups 1 of 366 days2025: Good 314 of 365 days2025: Moderate 51 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 year0501001502001995: 90th percentile AQI 1741996: 90th percentile AQI 1151997: 90th percentile AQI 1291998: 90th percentile AQI 1361999: 90th percentile AQI 1262000: 90th percentile AQI 1052001: 90th percentile AQI 1082002: 90th percentile AQI 1122003: 90th percentile AQI 872004: 90th percentile AQI 902005: 90th percentile AQI 872006: 90th percentile AQI 932007: 90th percentile AQI 1002008: 90th percentile AQI 842009: 90th percentile AQI 542010: 90th percentile AQI 742011: 90th percentile AQI 842012: 90th percentile AQI 732013: 90th percentile AQI 622014: 90th percentile AQI 642015: 90th percentile AQI 672016: 90th percentile AQI 612017: 90th percentile AQI 602018: 90th percentile AQI 612019: 90th percentile AQI 582020: 90th percentile AQI 482021: 90th percentile AQI 582022: 90th percentile AQI 552023: 90th percentile AQI 612024: 90th percentile AQI 572025: 90th percentile AQI 521995: Median AQI 1151996: Median AQI 441997: Median AQI 411998: Median AQI 421999: Median AQI 412000: Median AQI 372001: Median AQI 402002: Median AQI 412003: Median AQI 362004: Median AQI 372005: Median AQI 392006: Median AQI 402007: Median AQI 402008: Median AQI 392009: Median AQI 362010: Median AQI 402011: Median AQI 402012: Median AQI 412013: Median AQI 432014: Median AQI 462015: Median AQI 452016: Median AQI 452017: Median AQI 472018: Median AQI 402019: Median AQI 432020: Median AQI 362021: Median AQI 412022: Median AQI 432023: Median AQI 442024: Median AQI 402025: Median AQI 391995200020052010201520202025
  • 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
Ozone28378%
Fine particles (PM2.5)8222%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365314510000395284Ozone
20243662947110004057108Ozone
20233652689043004461179Ozone
2022365274910000435593Ozone
20213652877710004158105Ozone
2020365339260000364884Ozone
20193652818130004358126Ozone
20183652838011004061151Ozone
20173652121530000476090PM2.5
201636623612730004561122PM2.5
201536523313110004567105Ozone
20143652181470000466490Ozone
201336525810520004362108Ozone
201236525394143104173208Ozone
201131824652191004084156Ozone
20103552727481004074182Ozone
20093613154240003654112Ozone
200836327368220003984150Ozone
2007344249652910040100156Ozone
200636325977261004093156Ozone
200535626960234003987164Ozone
200436327761232003790159Ozone
200334727051194303687227Ozone
20023622437230152041112203Ozone
2001364257663281040108201Ozone
2000362260603480037105195Ozone
19993642466925222041126202Ozone
19983612227930291042136201Ozone
19973632465736222041129205Ozone
1996212131452790044115190Ozone
199554914171400115174190Ozone

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 1995–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem