Data / Rankings / Share of days unhealthy for sensitive groups or worse (US EPA AQI) / Counties in Maryland

Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI)

Baltimore County had the highest share of days unhealthy for sensitive groups or worse (US EPA AQI) of 16 counties in 2023, at 3.6%. Calvert County had the lowest, at 0.4%. The median was 1.7%. Source: EPA.

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Highest3.6Baltimore County
Lowest0.4Calvert County
Median1.716 counties

Map of counties, 2023

Anne Arundel County: 0.8 %Baltimore County: 3.6 %Calvert County: 0.4 %Carroll County: 1.6 %Cecil County: 1.7 %Charles County: 0.8 %Dorchester County: 1.9 %Frederick County: 2.6 %Garrett County: 0.6 %Harford County: 2.8 %Howard County: 1.1 %Kent County: 1.9 %Montgomery County: 1.4 %Prince George's County: 3 %Washington County: 1.7 %Baltimore city: 1.9 %
  • Under 0.8
  • 0.8 to 1.6
  • 1.6 to 1.9
  • 1.9 to 2.6
  • 2.6 and over
  • No data
%, 2023. Hatched areas have no value for this period. Source: Invokely calculation with data from EPA. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2023

Baltimore County: 3.6 %Baltimore County3.6Prince George's County: 3 %Prince George's County3Harford County: 2.8 %Harford County2.8Frederick County: 2.6 %Frederick County2.6Baltimore city: 1.9 %Baltimore city1.9Dorchester County: 1.9 %Dorchester County1.9Kent County: 1.9 %Kent County1.9Cecil County: 1.7 %Cecil County1.7Washington County: 1.7 %Washington County1.7Carroll County: 1.6 %Carroll County1.6Montgomery County: 1.4 %Montgomery County1.4Howard County: 1.1 %Howard County1.1Anne Arundel County: 0.8 %Anne Arundel County0.8Charles County: 0.8 %Charles County0.8Garrett County: 0.6 %Garrett County0.6Calvert County: 0.4 %Calvert County0.4Baltimore County: 3.6 %Baltimore County3.6Prince George's County: 3 %Prince George's County3Harford County: 2.8 %Harford County2.8Frederick County: 2.6 %Frederick County2.6Baltimore city: 1.9 %Baltimore city1.9Dorchester County: 1.9 %Dorchester County1.9Kent County: 1.9 %Kent County1.9Cecil County: 1.7 %Cecil County1.7Washington County: 1.7 %Washington County1.7Carroll County: 1.6 %Carroll County1.6Montgomery County: 1.4 %Montgomery County1.4Howard County: 1.1 %Howard County1.1Anne Arundel County: 0.8 %Anne Arundel County0.8Charles County: 0.8 %Charles County0.8Garrett County: 0.6 %Garrett County0.6Calvert County: 0.4 %Calvert County0.4
%. Source: Invokely calculation with data from EPA. Retrieved 2026-10-12.

Full ranking

RankCounties2023 (%)Change on 2022
1Baltimore County3.6+3.3 pts
2Prince George's County3+2.7 pts
3Harford County2.8+2.8 pts
4Frederick County2.6+2.2 pts
5Baltimore city1.9+1.3 pts
5Dorchester County1.9+1.9 pts
5Kent County1.9+1.9 pts
8Cecil County1.7+1.4 pts
8Washington County1.7+1.7 pts
10Carroll County1.6+1.2 pts
11Montgomery County1.4+1.1 pts
12Howard County1.1+1.1 pts
13Anne Arundel County0.8+0.8 pts
13Charles County0.8+0.8 pts
15Garrett County0.6+0.6 pts
16Calvert County0.4+0.4 pts

Other periods

About this ranking

Days with a daily Air Quality Index above 100 (unhealthy for sensitive groups, unhealthy, very unhealthy or hazardous) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; the counts are stored with each value.

Use the share rather than the number of days to compare counties, since the days with an AQI differ. 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.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 3 counties with data in other periods have no value for 2023 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. 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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts (Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023) [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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts, Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_maryland_by_2023,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023}},
  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/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. 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: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts: Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI), 2023
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/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/unhealthy-air-quality-days-share/maryland-counties?period=2023.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Rank Counties in Maryland by share of days unhealthy for sensitive groups or worse (US EPA AQI) using official data, and cite the source.
rank_places {"indicator":"aqi_unhealthy_sensitive_or_worse_days_share","level":"province","within":"Maryland","limit":10}
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Questions

Which county has the highest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Baltimore County, with 3.6% in 2023, according to EPA.

Which county has the lowest share of days unhealthy for sensitive groups or worse (US EPA AQI)?

Calvert County, with 0.4% in 2023.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: days with an AQI above 100 as a share of days with an AQI, calculated with stored counts. Retrieved 2026-10-12. 3 counties have no value for 2023 and are not ranked.

Share of days unhealthy for sensitive groups or worse (US EPA AQI): other rankings

Counties in Maryland: more rankings