Measurements taken at the US Embassy in Delhi put the city's Air Quality Index at 999 on Monday, off the standard chart, which finishes at the "hazardous" level of 500.
By comparison, the highest AQI level recorded Monday in Baoding -- China's most polluted city -- was 298.
Beijing was a pleasant 30, while India's next most polluted city, coal and industry-heavy Chandrapur, recorded levels of 824, according to the World Air Quality Index.
Research released earlier this year found that air quality levels exceed World Health Organizations guidelines for 80% of those living in urban areas around the world.
Protests and pollution masks
In Khan Market, one of Delhi's trendiest areas, shops that specialized in anti-pollution masks were doing brisk business as people queued up to buy some modicum of protection from the toxic smog.
On Sunday, hundreds of people gathered to protest outside Parliament in the city center as others voiced their displeasure online, posting to Twitter with the slogan #MyRightToBreathe.
An emergency ruling issued over the weekend saw more than 5,000 schools closed and construction work halted for the next three days. Officials warned that the number of vehicles allowed on the streets may be restricted if the situation does not improve.