Data / Median Air Quality Index (US EPA) / Harford County

Median Air Quality Index (US EPA) in Harford County

Median Air Quality Index (US EPA) in Harford County was 42 in 2025, according to the U.S. Environmental Protection Agency. That is unchanged from 2024. That is the 3rd highest of 16 counties in 2025.

2025, index42
Change on 20240
Rank3rd of 16Counties in Maryland ranked
Series high542011
Series low271981

Next release: Tuesday, 13 July 2027, estimated by Invokely from past publication dates (low confidence), not announced by the publisher. Release calendar

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Median Air Quality Index (US EPA) in Harford County, 1980 to 2025

203040506019801987199420012008201520251980: 39 index1981: 27 index1982: 36 index1983: 36 index1984: 35 index1985: 29 index1986: 31 index1987: 38 index1988: 38 index1989: 31 index1990: 35 index1991: 39 index1992: 35 index1993: 37 index1994: 38 index1995: 39 index1996: 37 index1997: 39 index1998: 39 index1999: 40 index2000: 39 index2001: 47 index2002: 44 index2003: 43 index2004: 51 index2005: 53 index2006: 50 index2007: 53 index2008: 49 index2009: 46 index2010: 50 index2011: 54 index2012: 54 index2013: 50 index2014: 52 index2015: 48 index2016: 48 index2017: 47 index2018: 42 index2019: 45 index2020: 41 index2021: 46 index2022: 43 index2023: 45 index2024: 42 index2025: 42 index203040506019801996201220251980: 39 index1981: 27 index1982: 36 index1983: 36 index1984: 35 index1985: 29 index1986: 31 index1987: 38 index1988: 38 index1989: 31 index1990: 35 index1991: 39 index1992: 35 index1993: 37 index1994: 38 index1995: 39 index1996: 37 index1997: 39 index1998: 39 index1999: 40 index2000: 39 index2001: 47 index2002: 44 index2003: 43 index2004: 51 index2005: 53 index2006: 50 index2007: 53 index2008: 49 index2009: 46 index2010: 50 index2011: 54 index2012: 54 index2013: 50 index2014: 52 index2015: 48 index2016: 48 index2017: 47 index2018: 42 index2019: 45 index2020: 41 index2021: 46 index2022: 43 index2023: 45 index2024: 42 index2025: 42 index
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12, published 2026-07-13.
All 46 values
Periodindex
202542
202442
202345
202243
202146
202041
201945
201842
201747
201648
201548
201452
201350
201254
201154
201050
200946
200849
200753
200650
200553
200451
200343
200244
200147
200039
199940
199839
199739
199637
199539
199438
199337
199235
199139
199035
198931
198838
198738
198631
198529
198435
198336
198236
198127
198039

Harford County compared with nearby places

Anne Arundel County: 40 indexBaltimore County: 45 indexCalvert County: 38 indexCarroll County: 38 indexCecil County: 41 indexCharles County: 38 indexDorchester County: 39 indexFrederick County: 41 indexGarrett County: 39 indexHarford County: 42 indexHoward County: 33 indexKent County: 38 indexMontgomery County: 39 indexPrince George's County: 40 indexWashington County: 40 indexBaltimore city: 43 index
  • Under 38
  • 38 to 39
  • 39 to 40
  • 40 to 41
  • 41 and over
  • No data
Median Air Quality Index (US EPA), 2025, index. Harford County is outlined. Same source and period for every area shown. Source: U.S. Environmental Protection Agency. Boundaries: U.S. Census Bureau cartographic boundary files.

Rankings

Definition

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

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How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Median Air Quality Index (US EPA), Harford County, 1980 to 2025) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Harford County, 1980 to 2025. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/en/median-air-quality-index/harford-county-maryland. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Median Air Quality Index (US EPA), Harford County, 1980 to 2025. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/en/median-air-quality-index/harford-county-maryland.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Harford County, 1980 to 2025 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/en/median-air-quality-index/harford-county-maryland (Accessed: 12 October 2026).

BibTeX
@misc{environmental_median_air_quality_index_2025,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Harford County, 1980 to 2025}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/harford-county-maryland. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Median Air Quality Index (US EPA), Harford County, 1980 to 2025
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/en/median-air-quality-index/harford-county-maryland
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/harford-county-maryland.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

What is the median Air Quality Index (US EPA) in Harford County?

Median Air Quality Index (US EPA) in Harford County was 42 in 2025, according to the U.S. Environmental Protection Agency. That is unchanged from 2024. That is the 3rd highest of 16 counties in 2025.

Where does this figure come from?

U.S. Environmental Protection Agency. EPA AirData annual AQI by county: median daily AQI. Retrieved by Invokely on 2026-10-12.

What was the highest median Air Quality Index (US EPA) in Harford County?

54 in 2011, the highest value since 1980 in this series.

Related statistics for Harford County

All statistics for Harford County | Harford County in figures