Toxic haze in Delhi despite 'green' Diwali

Levels between 101 and 200 are considered moderate, while those between 201 and 300 are "poor". Between 301 and 400 is categorised as "very poor" and a figure higher than 400 is considered "severe". The World Health Organization's guidelines say that exposure to PM 2.5 over a 24-hour-period should b...

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