The air quality index (AQI) in Delhi has plunged into the severe category with a count of 404 in the early hours of Wednesday. Noida is even worse with the PM 10 count at 582 and PM 2.5 count of 511, much higher than Delhi.

The PM 10 count is at 435 in the severe category and is only expected to deteriorate in the coming days of the week. It will cross the 500-mark during the day and worsen in the following couple of days, going up to the 522-mark.

The PM 2.5 count is also in the very poor category at 247 and will worsen to cross the 300-mark in the coming days.

As per Safar India, AQI is forecasted to further deteriorate in Delhi to the higher end of the very poor category by Wednesday and Thursday and quite a few regions may even experience severe AQI for a shorter time period, especially during early morning. Secondary particulate formation mechanism (which rapidly multiplies particulate pollution) is forecasted not to be triggered at present.

The overall air quality has deteriorated to the higher end of the very poor category as forecasted. Surface-level winds are low and Westerly. Surface winds are likely to further slow down and surface inversion is likely to form. Under the calm wind-cold conditions, fog formation is likely in the region, Safar India said.

This would be mainly radiative fog as a result of locally generated favourable weather conditions and may not persist for long. Slowing of dispersion owing to low ventilation is forecasted for the next two days.

At Mathura Road in Delhi, AQI is in the severe category with PM 10 of 509 and PM 2.5 of 456. Lodhi Road is better in the very poor category with PM 10 of 375 and PM 2.5 of 395.

During the day on Tuesday, AQI was in the severe category at several places. It was 527 at Patparganj, 522 in Sriniwaspuri, 528 in Noida, 575 in Faridabad, 547 in Anand Vihar, and 399 at Mandir Marg, which was the best reading in the city.