Indian capital city New Delhi's overall air quality has deteriorated to the "Poor" category, showed the data by the System of Air Quality and Weather Forecasting And Research on Sunday.
Some of the areas in and around New Delhi remained in the "Very Poor" category, the data suggested.
It forecast that Delhi's air quality will remain between the "Poor" category and the lower end of the "Very Poor" category until the Diwali festival, to be celebrated on Monday amid the bursting of smoke-emitting firecrackers.
However, the bursting of firecrackers is banned in the Indian capital. The country's top court, the Supreme Court of India, had recently refused to hear a plea seeking the removal of a blanket ban on firecrackers in Delhi for the Diwali festival.
A report by "India Today" said that the air quality is likely to plummet to the "Very Poor" category by Monday.
A blanket of smoke and fog has been witnessed over Delhi and its surrounding areas over the past few days.
High levels of air pollution are witnessed in the Indian capital during the winter months of October to February. Construction and demolition activities, burning of stubble by farmers in the states of Haryana and Punjab, and vehicular pollution are some of the reasons often cited for air pollution in Delhi.