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Understanding the Air Quality Index: A Beginner's Guide

June 17, 2026 · The Clime Team
Understanding the Air Quality Index: A Beginner's Guide

The Air Quality Index (AQI) is a standardized system used to communicate the quality of outdoor air and its potential health impacts. Developed by the U.S. Environmental Protection Agency (EPA), the AQI provides a clear and concise way to understand air pollution levels and take necessary precautions.

What Does the AQI Measure?

The AQI evaluates the concentration of five major air pollutants:

  • Ground-level ozone: A harmful pollutant formed when sunlight reacts with pollutants from vehicles and industrial emissions.
  • Particulate matter (PM2.5 and PM10): Tiny particles from sources like smoke, power plants, and vehicle exhaust.
  • Carbon monoxide: A colorless, odorless gas produced by burning fossil fuels.
  • Sulfur dioxide: A gas from burning fossil fuels and industrial processes.
  • Nitrogen dioxide: A gas from vehicle emissions and industrial processes.

Each pollutant's concentration is converted into an AQI value, and the highest value determines the overall AQI for that location. (airnow.gov)

How Is the AQI Calculated?

The AQI is calculated by measuring the concentration of each pollutant and converting it into an AQI value using specific formulas. The highest AQI value among all pollutants determines the overall AQI for that location. (airnow.gov)

Understanding AQI Levels

The AQI scale ranges from 0 to 500, divided into six categories, each associated with a color and health advisory:

  • 0 to 50 (Good): Air quality is satisfactory, posing little or no risk.
  • 51 to 100 (Moderate): Air quality is acceptable; however, there may be a risk for some individuals sensitive to air pollution.
  • 101 to 150 (Unhealthy for Sensitive Groups): Sensitive individuals may experience health effects; the general public is less likely to be affected.
  • 151 to 200 (Unhealthy): Everyone may begin to experience health effects; sensitive groups may experience more serious effects.
  • 201 to 300 (Very Unhealthy): Health alert; everyone may experience more serious health effects.
  • 301 and higher (Hazardous): Health warning of emergency conditions; the entire population is more likely to be affected.

These categories help individuals understand the potential health risks associated with current air quality levels. (airnow.gov)

Why Should You Pay Attention to the AQI?

Monitoring the AQI is crucial because air pollution can have immediate and long-term health effects, especially for sensitive groups such as children, older adults, and individuals with respiratory conditions. Even healthy individuals can experience adverse effects from prolonged exposure to polluted air. (lung.org)

How to Use the AQI to Protect Your Health

  • Stay Informed: Regularly check the AQI for your area through local news, weather reports, or online resources.
  • Limit Outdoor Activities: On days with higher AQI levels, especially in the "Unhealthy" category and above, reduce outdoor activities or stay indoors.
  • Protect Sensitive Individuals: Ensure that children, older adults, and those with respiratory conditions are aware of the AQI and take necessary precautions.
  • Advocate for Clean Air: Support policies and initiatives aimed at reducing air pollution to improve overall air quality.

By understanding and monitoring the AQI, you can make informed decisions to safeguard your health and the health of those around you.

Highlights:

Frequently Asked Questions