Data / Median Air Quality Index (US EPA) / New Castle County

Median Air Quality Index (US EPA) in New Castle County

Median Air Quality Index (US EPA) in New Castle County was 44 in 2025, according to the U.S. Environmental Protection Agency. That is up 1 from 2024.

2025, index44
Change on 2024+1
Series high672001
Series low341981

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 New Castle County, 1980 to 2025

304050607019801987199420012008201520251980: 59 index1981: 34 index1982: 47 index1983: 51 index1984: 51 index1985: 57 index1986: 47 index1987: 57 index1988: 47 index1989: 47 index1990: 47 index1991: 44 index1992: 37 index1993: 43 index1994: 44 index1995: 43 index1996: 41 index1997: 41 index1998: 42 index1999: 61 index2000: 61 index2001: 67 index2002: 61 index2003: 60 index2004: 60 index2005: 61 index2006: 58 index2007: 59 index2008: 57 index2009: 53 index2010: 55 index2011: 56 index2012: 55 index2013: 52 index2014: 54 index2015: 52 index2016: 52 index2017: 50 index2018: 48 index2019: 47 index2020: 46 index2021: 48 index2022: 48 index2023: 51 index2024: 43 index2025: 44 index304050607019801996201220251980: 59 index1981: 34 index1982: 47 index1983: 51 index1984: 51 index1985: 57 index1986: 47 index1987: 57 index1988: 47 index1989: 47 index1990: 47 index1991: 44 index1992: 37 index1993: 43 index1994: 44 index1995: 43 index1996: 41 index1997: 41 index1998: 42 index1999: 61 index2000: 61 index2001: 67 index2002: 61 index2003: 60 index2004: 60 index2005: 61 index2006: 58 index2007: 59 index2008: 57 index2009: 53 index2010: 55 index2011: 56 index2012: 55 index2013: 52 index2014: 54 index2015: 52 index2016: 52 index2017: 50 index2018: 48 index2019: 47 index2020: 46 index2021: 48 index2022: 48 index2023: 51 index2024: 43 index2025: 44 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
202544
202443
202351
202248
202148
202046
201947
201848
201750
201652
201552
201454
201352
201255
201156
201055
200953
200857
200759
200658
200561
200460
200360
200261
200167
200061
199961
199842
199741
199641
199543
199444
199343
199237
199144
199047
198947
198847
198757
198647
198557
198451
198351
198247
198134
198059

New Castle County compared with nearby places

Kent County: 41 indexNew Castle County: 44 indexSussex County: 39 index
  • Under 40
  • 40 to 42
  • 42 and over
Median Air Quality Index (US EPA), 2025, index. New Castle 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.

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), New Castle 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), New Castle 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/new-castle-county-delaware. 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), New Castle 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/new-castle-county-delaware.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), New Castle 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/new-castle-county-delaware (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), New Castle 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/new-castle-county-delaware. 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), New Castle 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/new-castle-county-delaware
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/new-castle-county-delaware.
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 New Castle County?

Median Air Quality Index (US EPA) in New Castle County was 44 in 2025, according to the U.S. Environmental Protection Agency. That is up 1 from 2024.

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 New Castle County?

67 in 2001, the highest value since 1980 in this series.

Related statistics for New Castle County

All statistics for New Castle County | New Castle County in figures