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The Air Quality Index (AQI): categories and colors

Summary

The US AQI is the EPA's index for reporting outdoor air quality. It runs from 0 to over 300 in six color-coded categories, from Good (green, 0-50) to Hazardous (maroon, 301 and up). Values above 100 are unhealthy, first for sensitive groups and then for everyone. During wildfires, AirNow's Fire and Smoke Map shows smoke impacts.

Draft. License: CC BY 4.0 (this summary). Sources: [S1] AirNow (US EPA and partners), "AQI Basics" (public domain (US government work)).

Facts

• id: F1 claim: The US AQI is EPA's tool for communicating outdoor air quality and health; higher values mean more pollution and greater health concern. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F2 claim: Green, Good, 0-50: air quality is satisfactory with little or no risk. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F3 claim: Yellow, Moderate, 51-100: acceptable, though some unusually sensitive people may be at risk. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F4 claim: Orange, Unhealthy for Sensitive Groups, 101-150: sensitive groups may have health effects; the general public is less likely to be affected. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F5 claim: Red, Unhealthy, 151-200: some of the general public may have effects, and sensitive groups more serious effects. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F6 claim: Purple, Very Unhealthy, 201-300: a health alert with increased risk for everyone. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F7 claim: Maroon, Hazardous, 301 and higher: a health warning of emergency conditions. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F8 claim: For each pollutant, an AQI of 100 generally matches the short-term national air quality standard for protecting public health. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02

Caveats

• The AQI is calculated per pollutant (e.g. ozone, particle pollution); the reported value is for the worst one.
• Other countries use different indices; numbers are not directly comparable.

Pointers

• id: P1 answers: Current AQI and wildfire smoke map where: https://fire.airnow.gov/ access: free, public web page

@misc{iil_note_waeps3n1,
  author = {{iinventedlight Library}},
  title = {{The Air Quality Index (AQI): categories and colors}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-02},
  url = {https://iinventedlight.com/library/reference/us-gov/air-quality-index-aqi/},
  note = {Permanent ID iil:note:waeps3n1. License: CC-BY-4.0. Summary of https://www.airnow.gov/aqi/aqi-basics/.},
}

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