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

Median Air Quality Index (US EPA) in Trinity County

Median Air Quality Index (US EPA) in Trinity County was 31 in 2025, according to the U.S. Environmental Protection Agency. That is unchanged from 2024.

2025, index31
Change on 20240
Series high572017
Series low111987

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

Get an email when a new figure is out or this one is revised.
Keep it in a collection in your library.

Median Air Quality Index (US EPA) in Trinity County, 1987 to 2025

10203040506019871998200320082013201820251987: 11 index1988: 16 index1995: 15 index1996: 15 index1997: 14 index1998: 15 index1999: 18 index2000: 14 index2001: 17 index2002: 13 index2003: 15 index2004: 14 index2005: 11 index2006: 17 index2007: 14 index2008: 19 index2009: 17 index2010: 11 index2011: 34 index2012: 54 index2013: 34 index2014: 12 index2015: 12 index2016: 51 index2017: 57 index2018: 54 index2019: 23 index2020: 36 index2021: 38 index2022: 34 index2023: 31 index2024: 31 index2025: 31 index020406019872004201520251987: 11 index1988: 16 index1995: 15 index1996: 15 index1997: 14 index1998: 15 index1999: 18 index2000: 14 index2001: 17 index2002: 13 index2003: 15 index2004: 14 index2005: 11 index2006: 17 index2007: 14 index2008: 19 index2009: 17 index2010: 11 index2011: 34 index2012: 54 index2013: 34 index2014: 12 index2015: 12 index2016: 51 index2017: 57 index2018: 54 index2019: 23 index2020: 36 index2021: 38 index2022: 34 index2023: 31 index2024: 31 index2025: 31 index
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12, published 2026-07-13.
All 33 values
Periodindex
202531
202431
202331
202234
202138
202036
201923
201854
201757
201651
201512
201412
201334
201254
201134
201011
200917
200819
200714
200617
200511
200414
200315
200213
200117
200014
199918
199815
199714
199615
199515
198816
198711

Trinity County compared with nearby places

Amador County: 38 indexButte County: 46 indexCalaveras County: 40 indexColusa County: 40 indexDel Norte County: 32 indexEl Dorado County: 40 indexFresno County: 61 indexGlenn County: 40 indexHumboldt County: 38 indexImperial County: 64 indexInyo County: 55 indexKern County: 70 indexKings County: 57 indexLake County: 31 indexLos Angeles County: 74 indexMadera County: 50 indexMarin County: 21 indexMariposa County: 44 indexMendocino County: 38 indexMerced County: 50 indexMono County: 21 indexMonterey County: 38 indexNevada County: 42 indexOrange County: 53 indexPlacer County: 52 indexPlumas County: 45 indexRiverside County: 80 indexSacramento County: 49 indexSan Benito County: 39 indexSan Bernardino County: 77 indexSan Diego County: 67 indexSan Joaquin County: 46 indexSan Luis Obispo County: 50 indexSanta Barbara County: 52 indexSanta Cruz County: 35 indexShasta County: 44 indexSiskiyou County: 37 indexSolano County: 33 indexSonoma County: 9 indexStanislaus County: 51 indexSutter County: 47 indexTehama County: 38 indexTrinity County: 31 indexTulare County: 64 indexTuolumne County: 39 indexVentura County: 50 indexYolo County: 47 index
  • Under 36
  • 36 to 39
  • 39 to 45
  • 45 to 50
  • 50 to 58
  • 58 and over
  • No data
Median Air Quality Index (US EPA), 2025, index. Trinity 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.

Report a problem with this figure

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), Trinity County, 1987 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), Trinity County, 1987 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/trinity-county-california. 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), Trinity County, 1987 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/trinity-county-california.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Median Air Quality Index (US EPA), Trinity County, 1987 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/trinity-county-california (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), Trinity County, 1987 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/trinity-county-california. 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), Trinity County, 1987 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/trinity-county-california
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/en/median-air-quality-index/trinity-county-california.
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  -
Embed this chart

Paste this code into a web page or a blog post. The chart shows the latest figures as they are published, with the source and a link back to this page.

Sites that read oEmbed links, such as WordPress, can show the chart when you paste the link to this page.

Use this data in your AI agent

Invokely serves this figure to AI assistants through MCP and to code through a REST API, with the source and citation attached. Ask your assistant:

What is the latest median Air Quality Index (US EPA) in Trinity County? Cite the source.
get_value {"indicator":"aqi_median","place":"us-county-06105"}
GET https://invokely.ai/api/v1/value?indicator=aqi_median&place=us-county-06105

Connect Claude, ChatGPT or Cursor in one step. The trial answers 25 calls a day without an account.

Questions

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

Median Air Quality Index (US EPA) in Trinity County was 31 in 2025, according to the U.S. Environmental Protection Agency. That is unchanged 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 Trinity County?

57 in 2017, the highest value since 1987 in this series.

Related statistics for Trinity County

All statistics for Trinity County | Trinity County in figures