India, Nov. 2 -- The overall air quality index on November 1 afternoon was around 530

A public health emergency was declared in Delhi on the afternoon of November 1, 2019, after air quality plunged to 'severe plus' levels since the night of October 31.

On Friday, at around 11 am, the overall air quality index (AQI) was around 530.

An AQI between 0-50 is considered 'good', 51-100 'satisfactory', 101-200 'moderate', 201-300 'poor', 301-400 'very poor', and 401-500 'severe'. Above 500 is 'severe-plus' or 'emergency' category.

The levels of particulate matter (PM) 10 and 2.5 were above 500 and 300 microgramme per cubic metre (ug/m3) respectively, five times more than their prescribed standard.

Delhi has been shrouded in a thick blanket o...