About AQI

• Air Quality Index (AQI) is a number, which is a measure of air quality. 
• The higher the AQI, the worse the air. 
• The colour-coded AQI index was launched in India in 2014, and it helps the public and the government understand the condition of the air and what subsequent measures are to be taken to combat the situation, based on its severity. 
• There are six categories of AQI, namely ‘Good’ (0-50), ‘Satisfactory’ (50-100), ‘Moderately polluted’ (100-200), ‘Poor’ (200-300), ‘Very Poor’ (300-400), and ‘Severe’ (400-500).

Why in News?

• The Air Quality Index dropped below 400 (very poor category)in Delhi.

reference:

https://newsonair.gov.in/News?title=Air-Quality-in-Delhi-recorded-in-%26%2339%3bvery-poor%26%2339%3b-category-with-AQI-at-328&id=451479