Air quality in New Delhi worsened in the days after a grand festival and at a time when Prime Minister Narendra Modi was attending the COP 26 climate summit in Glasgow.

From "poor" air quality recorded on Nov 1, air quality in New Delhi slipped into "hazardous" by the weekend following Diwali, north India's greatest festival, according to the Central Pollution Control Board of the Ministry of Environment, Forest and Climate Change.

Air quality in New Delhi was in the "very poor" category on Nov 2 for the first time this season and the readings got worse in the following days. Despite a ban, people across the city lighted firecrackers late into Thursday night to celebrate Diwali, worsening pollution levels.

A thick layer of smog blanketed New Delhi, a city of nearly 20 million people, on Friday morning, and people from several parts of the city and its suburbs complained of itchy throat and watery eyes.

"People are walking into hospitals and clinics, saying they're breathless and heavy in the chest due to pollution over the past few days," said Rashmi Sama, a pulmonologist at the Sir Ganga Ram Hospital.

The PM2.5 concentration stood at the maximum reading of 999 per cubic meter in some parts of Delhi on Friday, according to the Earth Sciences Ministry's System of Air Quality and Weather Forecasting and Research. Several places recorded figures close to or higher than 500, which is categorized as "severe". Air quality index in various areas slipped to the "severe" category on Friday morning.

Farm fires, firecrackers

New Delhi's Environment Minister Gopal Rai said on Friday that the city's air quality had deteriorated due to a surge in farm fires and some people lighting firecrackers during Diwali despite a ban.

The Delhi government banned the sales and lighting of firecrackers this year to curb pollution levels.

Rampant incidents of stubble burning around New Delhi during this season have further aggravated the situation.

According to air quality information service SAFAR, stubble burning accounted for 36 percent of Delhi's PM2.5 on Friday, the highest so far this season.

Fire and smoke emanating from stubble burning in Punjab and Haryana states are carried by winds to Delhi, mixing with Delhi's own rising pollution.

Carbon dioxide emitted by 12 million vehicles in Delhi, industrial plants and billions of dust particles from construction sites are other major pollution sources in Delhi, according to government reports.

"It can be expected that smog episodes this year might have higher peak pollution if special steps are not taken to reduce pollution from the sources," stated a 2021 pre-winter analysis by the Centre for Science and Environment.