Air quality in northern Indian cities plummets at this time of year. It gets worst around Diwali, the biggest Hindu festival, celebrated with fireworks and firecrackers. Cool temperatures, farmers burning stubble and vehicle emissions are also major contributors to the miasma.

Toxic smog in Pakistan is so severe it can be seen from space. Record-breaking levels of smog have shrouded eastern Pakistan and northern India, forcing school closures and threatening public health.