What is the purpose of the Air Quality Index (AQI), and what do the color-coded categories represent?

• A. AQI measures wind speed; colors indicate pollution sources.
• B. AQI communicates how polluted the air is and associated health risks; categories range from Good to Hazardous with corresponding colors.
• C. AQI ranks cities by population size.
• D. AQI indicates impedance to air flow.

Answer: (B)

The main idea behind the Air Quality Index is to translate actual pollutant levels into a single, easy-to-understand signal that tells you how polluted the air is and what health risks come with exposure. The color-coded categories map AQI values to levels of concern: green for Good, yellow for Moderate, orange for Unhealthy for Sensitive Groups, red for Unhealthy, purple for Very Unhealthy, and maroon (or brown) for Hazardous. These colors give a quick visual cue about how much outdoor activity you might safely do, especially if you belong to a sensitive group like children, the elderly, or people with asthma or heart disease. The AQI pulls from multiple pollutants (like PM2.5, PM10, ozone, CO, SO2, NO2) and uses the highest pollutant-specific index to assign the overall value, so the most threatening pollutant determines the day’s category. This isn’t about wind speed, city population, or how air flows; it’s a communication tool about how polluted the air is and what health risks are associated with that level.