Sanchit Khanna/Hindustan Times/Getty Images via CNN Newsource

NEW DELHI -- Around 20 million people in India’s capital woke up on Wednesday breathing the most polluted air of any major city in the world, a day after celebrations for the Diwali festival , during which revelers typically set off fireworks and firecrackers.

As of Wednesday, New Delhi’s PM 2.5 concentration – a measure of pollutants in the air – was more than 40 times the World Health Organization’s annualized guideline level, according to Swiss air quality monitoring company IQAir.

New Delhi grapples with severe year-round pollution, but the winter months are typically worst, when millions of farmers in surrounding regions burn stubble in their fields to clear the way for the next crop.

The sharp deterioration in air

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