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Understanding the Air Quality Index: A Comprehensive Guide for the United States

June 18, 2026 · The Clime Team
Understanding the Air Quality Index: A Comprehensive Guide for the United States

The Air Quality Index (AQI) is a standardized system used to communicate the quality of air in a specific area, indicating how clean or polluted the air is and what associated health effects might be of concern. Developed by the U.S. Environmental Protection Agency (EPA), the AQI focuses on health effects that may be experienced within a few hours or days after breathing polluted air. (epa.gov)

What Does the AQI Measure?

The AQI measures the concentration of five major air pollutants regulated by the Clean Air Act:

  • Ground-level ozone (O₃): A reactive gas that forms when sunlight reacts with pollutants from vehicles and industrial emissions.
  • Particulate matter (PM₂.₅ and PM₁₀): Tiny particles or droplets in the air that can penetrate deep into the lungs and even enter the bloodstream.
  • Carbon monoxide (CO): A colorless, odorless gas produced by burning fossil fuels.
  • Sulfur dioxide (SO₂): A gas produced by burning fossil fuels and industrial processes.
  • Nitrogen dioxide (NO₂): A gas produced by burning fuel, especially in vehicles and power plants.

How Is the AQI Calculated?

The AQI is calculated by converting the concentration of each pollutant into a number on a scale from 0 to 500. The higher the AQI value, the greater the level of pollution and the greater the health concern. An AQI value of 100 generally corresponds to the level of the National Ambient Air Quality Standard for the pollutant. (epa.gov)

Understanding AQI Categories

The AQI is divided into six categories, each corresponding to a different level of health concern:

  • 0–50 (Good): Air quality is satisfactory, and air pollution poses little or no risk.
  • 51–100 (Moderate): Air quality is acceptable; however, there may be some health concern for a small number of unusually sensitive individuals.
  • 101–150 (Unhealthy for Sensitive Groups): Members of sensitive groups may experience health effects. The general public is less likely to be affected.
  • 151–200 (Unhealthy): Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
  • 201–300 (Very Unhealthy): Health alert: everyone may experience more serious health effects.
  • 301–500 (Hazardous): Health warning of emergency conditions: everyone is more likely to be affected. (epa.gov)

How to Interpret AQI Values

Each AQI value is associated with a specific color to help you quickly understand the air quality:

  • Green (0–50): Good
  • Yellow (51–100): Moderate
  • Orange (101–150): Unhealthy for Sensitive Groups
  • Red (151–200): Unhealthy
  • Purple (201–300): Very Unhealthy
  • Maroon (301–500): Hazardous (epa.gov)

Health Implications of AQI Levels

Understanding the health implications of different AQI levels is crucial for protecting yourself and others:

  • Good (0–50): Air quality is satisfactory, and air pollution poses little or no risk.
  • Moderate (51–100): Air quality is acceptable; however, there may be some health concern for a small number of unusually sensitive individuals.
  • Unhealthy for Sensitive Groups (101–150): Members of sensitive groups may experience health effects. The general public is less likely to be affected.
  • Unhealthy (151–200): Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
  • Very Unhealthy (201–300): Health alert: everyone may experience more serious health effects.
  • Hazardous (301–500): Health warning of emergency conditions: everyone is more likely to be affected. (epa.gov)

How to Monitor and Improve Air Quality

Monitoring air quality is essential for making informed decisions about outdoor activities and health precautions. Clime offers advanced air quality monitoring solutions that provide real-time AQI data, forecasts, and historical trends. By leveraging Clime's technology, you can stay informed about air quality conditions in your area and take appropriate actions to protect your health.

Conclusion

The Air Quality Index is a vital tool for understanding and managing air quality. By staying informed about AQI levels and utilizing resources like Clime's monitoring solutions, you can make proactive decisions to safeguard your health and well-being.

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