The air quality in Delhi continued to remain in the “severe” category on Friday despite an improvement in pollution levels by 1 pm, PTI reported. An Air Quality Index reading between 0-50 is considered good, 51-100 is considered satisfactory, 101-200 moderate, 201-300 poor, 301-400 very poor and 401-500 is severe or hazardous.

The Central Pollution Control Board said the overall air quality recorded was 428. The System of Air Quality and Weather Forecasting And Research, or SAFAR, said low surface wind speed had slowed down the recovery process, PTI reported. “At present, it continues to be in ‘severe’ but likely to improve further and will become ‘very poor’ by afternoon and will improve further by Saturday,” the Centre-run research institute said.

A report by research group Urban Emissions said as much as 50 lakh kg of firecrackers were burnt in the National Capital Region, emitting 1.5 lakh kg of PM2.5 matter – airborne particles with a diameter of less than 2.5 micrometres – the Hindustan Times reported. These particles are about 30 times finer than a human hair and can cause respiratory diseases and other ailments if inhaled.

On Thursday, air quality in the city reached the “severe plus” emergency category because of smog caused by firecrackers burst during Diwali. There were several violations of the Supreme Court order, with people bursting fireworks outside the two-hour limit mandated by the court. The court had also instructed that only “green fireworks” be burst between 8 pm and 10 pm on Diwali. However, firecracker manufacturers had said there was “no such thing”. Violations of the order were reported from across the National Capital Region, and fireworks were burst the day after Diwali, on Thursday, too.