What is an air quality index (AQI)?

An air quality index (AQI) is fundamentally a system used to communicate air quality levels to the public. This index translates complex air quality data, which includes measurements of various pollutants such as particulate matter, ground-level ozone, carbon monoxide, and sulfur dioxide, into a simple numerical scale and corresponding color-coded system that indicates how polluted the air currently is or how polluted it is forecast to become.

The AQI is designed to provide an understandable way for individuals to assess how different levels of air pollution might affect their health and activities. For instance, a higher AQI value indicates poorer air quality, which may pose health risks, especially to sensitive populations. This system is vital for informing the public, allowing them to take precautionary measures when air quality is poor.

The other options, while related to environmental measurements, do not accurately describe the air quality index. For example, measuring humidity levels pertains to weather observations, calculating carbon emissions deals with greenhouse gases and climate impact rather than direct air quality assessments, and assessing water quality relates strictly to aquatic environments, not air quality. Thus, the focus and purpose of AQI clearly fit the description of a system for conveying air quality levels.