The air is almost impossible to breathe in Delhi these days due to the oppressive layer of toxic smog that covers the entire city. Delhi's Air Quality Index (AQI) shot up to 481 on Monday, solidly putting it in the "severe plus" range. For comparison, an AQI of 401 is the starting point for the "severe" category, and levels above 450 pose serious health risks, even for healthy people.

With an air quality score of 1,081, Delhi currently holds the sobering title of the most polluted city in the world, according to live rankings by Swiss group IQAir. This "hazardous" level is a startling 130.9 times higher than the WHO's recommended PM2.5 limit.
Delhi's pollution problem has multiple causes:

Burning stubble: According to SAFAR (System of Air Quality and Weather Forecasting and Research), burning crop residue was responsible for 25% of the city's air pollution on Saturday and 40% on Sunday. Satellites recorded a four-day high of 1,334 stubble-burning incidents in six northern states on Sunday.
Vehicles: According to the Center's Decision Support System for Air Quality Management, 15.8% of Delhi's pollution on Sunday came from vehicle emissions.

PM2.5, a very dangerous pollutant, continues to be the main contributor to industrial emissions and construction dust. This microscopic pollutant can lead to serious respiratory and cardiovascular problems because it enters the lungs deeply.