Smog in and around the cities of Lahore and New Delhi has reached new stretch over the past few days.

The recent burning of crops in northern India, combined with fog, dust and air pollution from vehicles and factories, has resulted in a thick layer of smog covering several cities in India and Pakistan.



It's one of the worst cases of air pollution in India and New Delhi has declared a public health emergency, closing down schools and offices.



The following graphic shows satellite imagery of the smog in contrast with the aerosol optical thickness (AOD) in the affected areas, which reflects the amount of pollutants available in the air.