The Air Quality Index compresses six pollutants into a single number between 0 and 500 and six named colour bands — Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, Hazardous. It was built to be acted on, not admired.

This system takes its cues from the places the AQI actually lives: the white weather page of a newspaper and the white card in a phone app. White ground, a humanist federal sans, hairline rules, and one saturated six-segment bar that always arrives with its number and a sentence telling you whether to go outside.