New Delhi: A thick toxic haze or ‘smog’ returned to Delhi, Noida, Gurugram and surrounding places on Monday morning, after people burst crackers on Diwali night, violating the Supreme Court’s ban order, leading to heavy pollution all across the National Capital Region – which has been already battling with its deteriorating air quality.

Most realtime air monitoring platforms this morning pegged the air quality index (AQI) above 500, with some places reaching as high as 900. Jawaharlal Nehru Stadium recorded an AQI of 910, Lajpat Nagar 959 and Karol Bagh 779 around 6 am.

The average AQI was around 300 at most places, according to data recorded by the Central Pollution Control Board (CPCB). The PM2.5 and PM10 pollutant levels touched 500 at most places during the day, including in Rohini, ITO, and Delhi airport area.

According to the Central Pollution Control Board (CPCB), while the average AQI remained very poor (312) in Anand Vihar at 8am on Monday, PM2.5 levels touched 488. Similarly, RK Puram saw an AQI of 305 at 8am, with PM2.5 being the most prominent pollutant touching 455. The concentration of PM 2.5 in the city has been recorded at 20 times the limit prescribed by the World Health Organisation, prompting the city government to order the closure of all primary classes and restrict the entry of trucks.

Delhi, where the air quality ranks among the worst in the world’s capital cities, was cloaked in a thick blanket of smog with severe pollution levels for a week since October 28. The government had to shut schools and ban diesel trucks in view of the pollution, though it stopped short of enforcing the odd-even rule.

A  western disturbance brought rain over most parts of northwest India late last week, which reduced the contribution of smoke from stubble burning in Punjab and Haryana to Delhi’s air pollution. The weather office had earlier predicted a marginal improvement in air quality ahead of Diwali due to the light rain.