Air quality index

An air quality index is a numerical scale that summarizes ambient air pollution and communicates the potential health effects of current or forecast conditions. Its pollutants, breakpoints, and categories vary by jurisdiction.

Air pollutant: A substance in the atmosphere at a concentration that can harm people, ecosystems, or materials. Index calculations start with measurements of specific pollutants in ambient air.
Air quality alert: A public notice that air pollution has reached or is expected to reach levels of concern. Authorities use index thresholds to trigger timely warnings.
United States Air Quality Index: The U.S. Environmental Protection Agency's scale for reporting daily air pollution and associated health concern. It is a prominent national implementation, with its own breakpoints and categories.
Air pollution and health: The effects of polluted air on human health, ranging from short-term irritation to chronic disease and premature death. Health effects provide the rationale for translating pollution readings into risk categories.
Air pollution mixture: The combination of pollutants present in air, whose components can interact and vary together. A single index value may conceal risks from mixtures of pollutants.
Particulate matter: A mixture of airborne solid particles and liquid droplets, classified by size such as PM₂.₅ and PM₁₀. Fine and coarse particles are commonly tracked as separate index pollutants.
Sensitive group: A population more likely to experience health effects from a given environmental exposure. Index advice often identifies groups more vulnerable to polluted air.
European Air Quality Index: A European Environment Agency scale that reports air pollution levels using pollutant-specific bands. Its design and category conventions differ from the U.S. system.
Air pollution episode: A period when air pollution rises substantially above typical local levels. Index spikes make short-lived episodes visible in public reporting.
Personal air pollution monitoring: Measurement of pollutant exposure near an individual using portable or wearable instruments. Personal measurements can differ from the area readings underlying public index reports.

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