Understanding AQI Categories: A Guide for Non-Technical Users

The Air Quality Index (AQI) is a standardized system used to communicate the quality of air in a specific area and its potential health impacts. Developed by the U.S. Environmental Protection Agency (EPA), the AQI simplifies complex air pollution data into a single value, making it easier for the public to understand and respond appropriately.

What Does the AQI Measure?

The AQI evaluates concentrations of five major air pollutants regulated by the Clean Air Act:

• Ground-level ozone (O₃)
• Particulate matter (PM₂.₅ and PM₁₀)
• Carbon monoxide (CO)
• Sulfur dioxide (SO₂)
• Nitrogen dioxide (NO₂)

Each pollutant has specific health standards, and the AQI provides a unified scale to assess their combined impact on air quality.

How Is the AQI Calculated?

The AQI is calculated by converting the concentration of each pollutant into an AQI value using established breakpoints. The highest AQI value among these pollutants determines the overall AQI for that area. This method ensures that the AQI reflects the most significant health risk present at any given time.

Understanding AQI Categories

The AQI scale ranges from 0 to 500, divided into six color-coded categories, each representing a different level of health concern:

• 0 to 50 (Green): Good

• Air quality is satisfactory, and air pollution poses little or no risk.

• 51 to 100 (Yellow): Moderate

• Air quality is acceptable; however, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.

• 101 to 150 (Orange): Unhealthy for Sensitive Groups

• Members of sensitive groups may experience health effects. The general public is less likely to be affected.

• 151 to 200 (Red): Unhealthy

• Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.

• 201 to 300 (Purple): Very Unhealthy

• Health alert: The risk of health effects is increased for everyone.

• 301 and higher (Maroon): Hazardous

• Health warning of emergency conditions: everyone is more likely to be affected.

These categories help individuals quickly assess air quality and take necessary precautions. (airnow.gov)

Health Implications of Each AQI Category

• Good (0–50): Air quality is excellent, posing little or no risk. It's a great time to enjoy outdoor activities.

• Moderate (51–100): Air quality is acceptable for most people. However, sensitive individuals, such as those with pre-existing respiratory conditions, may experience mild symptoms like coughing or shortness of breath.

• Unhealthy for Sensitive Groups (101–150): Sensitive groups, including children, older adults, and people with heart or lung conditions, may experience health effects. The general public is less likely to be affected.

• Unhealthy (151–200): Everyone may begin to experience health effects, and sensitive groups may experience more serious effects.

• Very Unhealthy (201–300): Health alert: The risk of health effects is increased for everyone.

• Hazardous (301 and higher): Health warning of emergency conditions: everyone is more likely to be affected.

Understanding these categories enables individuals to make informed decisions about outdoor activities and take appropriate health precautions. (airnow.gov)

How to Use AQI Information

• Stay Informed: Regularly check local AQI readings, especially if you belong to sensitive groups.

• Limit Exposure: On days when the AQI is in the 'Unhealthy' or higher categories, reduce outdoor activities, particularly strenuous ones.

• Protect Sensitive Individuals: Ensure that children, the elderly, and those with respiratory conditions are aware of the AQI and take necessary precautions.

• Stay Updated: AQI levels can change throughout the day due to weather conditions and pollution sources. Stay updated with real-time information.

By understanding and monitoring AQI categories, individuals can take proactive steps to protect their health and well-being.

Highlights:

• What is the air quality index (AQI)? | IQAir, Published on Wednesday, December 03
• Communicating Air Quality Conditions: The Air Quality Index | US EPA, Published on Monday, September 29