New Delhi [India], December 4 (ANI): The Air Quality in Delhi which has been in the 'severe' category for some time is likely to improve bringing respite to Delhiites from Sunday evening, a weather scientist said.

"The air quality in the national capital is in the severe category with an air quality index of around 400, but from today evening onwards, the air quality of the national capital is likely to improve," India Meteorological Department (IMD) scientist Vijay Soni told ANI.

During a telephonic conversation, Vijay Soni, a scientist at the IMD's Air Quality Division in New Delhi, said, "Today morning the air quality of Delhi was in the severe category with an Air Quality Index (AQI) around 400.

"The main reason behind this has been with winds remaining calm for the whole day and night on Saturday, which deteriorated air quality significantly.""But today (Sunday) we expect that winds will improve and we will see an improvement in the AQI from evening onwards," he said.

Explaining the two main reasons for air quality to be in a severe category, Soni said, "The main reason is low wind speed and decrease in mixing layer height.

"The mixing layer height has come down significantly close to the surface. So these two factors are really contributing to the deterioration in air quality."He explained, "Mixing height is the height up to which air pollutants get mixed up in the atmosphere. The wind is almost calm, but today morning it has started. Right now the wind speed is up to 8 kmph," Vijay Soni said.

On being asked if it's normal to have such air quality in the month of December in Delhi, Soni said, "The air quality generally deteriorates in the month of December. In this month generally, we see lower mixing height and low wind speed and hence we experience bad air quality." (ANI)