Understanding the Air Quality Index (AQI): A Quick Guide

The Air Quality Index (AQI) is a standardized system used to communicate daily air quality levels to the public. Developed by the U.S. Environmental Protection Agency (EPA), the AQI translates concentrations of common air pollutants into a scale that indicates potential health risks. (epa.gov)

What Does the AQI Measure?

The AQI focuses on 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.

• Carbon monoxide (CO): A colorless, odorless gas produced by combustion processes.

• Sulfur dioxide (SO₂): A gas produced by burning fossil fuels and industrial processes.

• Nitrogen dioxide (NO₂): A gas that forms from combustion processes, especially in vehicles and power plants.

How Is the AQI Calculated?

Each pollutant has its own sub-index, calculated based on its concentration in the air. The highest sub-index determines the overall AQI value for that location. The AQI scale ranges from 0 to 500, with higher values indicating greater health risks. (epa.gov)

AQI Categories and Health Implications

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

• 0–50 (Good): Air quality is satisfactory, posing little or no risk.

• 51–100 (Moderate): Air quality is acceptable; however, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.

• 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 and higher (Hazardous): Health warning of emergency conditions: everyone is more likely to be affected.

Why Is the AQI Important?

The AQI provides essential information about air quality, helping individuals make informed decisions to protect their health. By understanding the AQI, you can take appropriate actions, such as limiting outdoor activities or using air purifiers, especially when pollution levels are high. (epa.gov)

How Can You Stay Informed?

To monitor local air quality, you can use resources like the EPA's AirNow website, which offers real-time AQI data and forecasts for various locations. (airnow.gov)

Understanding the AQI empowers you to take proactive steps in safeguarding your health against the adverse effects of air pollution.

Highlights:

• Air quality index (AQI) | Description, EPA, Pollution, Smog, Health, & Facts | Britannica, Published on Monday, March 09
• Communicating Air Quality Conditions: The Air Quality Index | US EPA, Published on Monday, September 29
• Air Quality Index