Delhi's air quality worsened to the 'very poor' range on Sunday, with pollution levels increasing throughout the day. Stubble burning incidents in Punjab crossed 1,000 for the first time this season, contributing to the pollution load. Local sources of pollution within Delhi were identified as the main factor behind the city's poor air quality, with calm winds preventing the dispersal of emissions. Experts predict that Delhi's air quality is likely to remain in the 'very poor' category for the next few days, as strong winds are needed to disperse pollutants.