Delhi’s air quality index deteriorated to the “severe” category for the first time this year on Thursday 1 pm as the average AQI reading stood at 402, Hindustan Times reported quoting data from the Central Pollution Control Board. At 4 pm however, the air quality had improved to the “poor” category with the index reading 297.

On Thursday, sixteen monitoring stations, including at Shadipur (406), Patparganj (411), Jahangirpuri (429) and Vivek Vihar (432), recorded the air quality in the severe category, according to PTI.

Air quality enters the very poor zone between the 301-400 mark and crosses over to the severe zone after exceeding 400. Delhi’s average 24-hour air quality index reading was 297 on Wednesday, marginally down from Tuesday’s 312.

Speaking to Hindustan Times, VK Soni, head of India Meteorological Department’s environment monitoring research centre predicted that the city’s air will improve significantly between Friday and Sunday, with wind speeds likely to touch 15 kmph on Friday.

“There is a trough formation, which will lead to a significant improvement in wind speed over the Capital and this will lead to better dispersion of pollutants,” Soni said. “Till Sunday, the forecast is that we will see an improvement in air.”

A senior scientist at the India Meteorological Department told PTI that the wind speed dipped on Wednesday, which led to the accumulation of pollutants.

PM10 levels in Delhi-NCR stood at 420 microgram per cubic meter (g/m3) at 10 am, the highest this season so far, PTI reported. PM10 levels below 100 g/m3 are considered safe in India. PM10 is particulate matter with a diameter of 10 micrometers and is inhalable into the lungs. These particles include dust, pollen and mould spores. The levels of PM2.5, finer particles which can even enter the bloodstream, were 227 g/m3. The PM2.5 levels up to 60 g/m3 are considered safe.

According to the Ministry of Earth Sciences’ air quality monitor, SAFAR, the share of stubble burning in Delhi’s PM2.5 concentration was 18% on Wednesday. It was recorded at 23% on Tuesday, the maximum so far this season, PTI reported.

Meanwhile on Wednesday, President Ram Nath Kovind signed an ordinance to set up a commission to monitor the air quality in Delhi and its neighbouring states. Air pollution in the northern states has become an annual occurrence, with multiple states often blaming the other for factors that lead to a toxic smog across several places including in NCR, Uttar Pradesh and Haryana.