The AQI scale is divided into five categories: good (green), moderate (yellow), unhealthy for sensitive groups (orange), unhealthy (red), and extremely unhealthy (purple). The presence and amount of air pollutants changes during the day.

When the air contains very small quantities of pollutants, the air quality is good, so the AQI shows a green colour. On the contrary, when there are high quantities of pollutants in the air, the air quality is really bad and the AQI shows a purple colour.

The air is mostly clean when there are very few pollutants: there is no risk when we breathe or do outdoor activities. On the contrary, when there are many pollutants in the air it’s not clean: our health is at risk and we should avoid outdoor activities.

AQI is particularly useful for citizens and governments. By using the AQI, we can know the condition of the air and the environment. Citizens and governments can then take measures to protect their health.