Millions of masks have been issued to students in New Delhi as the Indian capital continues to be engulfed in thick smog. Air pollution in the city and surrounding towns have reached some of the worst levels seen so far in 2019.  Authorities say the smog is caused by fireworks set off during a Hindu festival during the last week of October, and smoke from farmers burning their fields in neighbouring states.  On November 1, 2019, the authorities declared a public health emergency and ordered…