Smog fills Delhi and northern India every winter, casting a shadow on Diwali celebrations and hitting peak tourism season. The region's position on the Indo-Gangetic Plain, where the Himalayas block air from flowing north, leads to trapped pollution from late October to February.

Air quality in Delhi reached an AQI of 581 on November 7, according to reports citing data from Swiss air monitoring company IQAir. That made it the most polluted major city in the world at that moment.

By the time of writing, Delhi's AQI hourly reported value had come down to 176, putting it second only to Lahore in Pakistan for poor air quality.

Masks have become a common sight as a temporary solution to the structural problem of pollution. Smog has now become a regular feature of traveling to northern India in winter, with no immediate plans for large-scale mitigation efforts reported.