Hyderabad, Nov. 9 -- Every winter, and especially after Diwali, one number dominates the headlines: the Air Quality Index (AQI). But what does a reading of 150, 300 or 500 actually mean for the air you breathe?

Here's everything you need to know about what actually AQI means and its impact on people's health.

What is AQI?

The AQI turns complicated pollution data into a single number, a name and a colour, so that ordinary people can understand how clean or dirty the air is. India's National Air Quality Index was launched in New Delhi in September 2014 under the Swachh Bharat Abhiyan.

The index considers eight pollutants, including fine particles known as PM2.5 and PM10. The overall AQI is set by whichever pollutant is worst at that mom...