Delhi's air quality saw a marginal improvement on Tuesday. The air quality index (AQI), the overall marker for the city's air pollution was 409 while on Monday it had touched 450. Although still in the severe category, it has declined to the lower ranges.

Among the industrial areas of outer Delhi where operations have been prohibited till Wednesday, the air quality showed improvements in Bawana and Narela where it was in the very poor range as opposed to severe on Monday. But, in Mundka, Wazirpur and Faridabad pollution was still in the severe category.

The low temperatures and high moisture level contributed to keeping pollution levels high on Tuesday. Ministry of Earth Science agency SAFAR (System of Air Quality and Weather Forecasting and Research) said Tuesday that meteorological conditions are becoming slowly favourable and severity of air pollution is on a decline.

In its forecast for the next few days, SAFAR said that surface wind speed is expected to increased from existing 2.3 kmph to 5 kmph. "SAFAR forecasting model predicts a faster improvement due to faster dispersion and deposition owing to a shorter lifetime of particles near the surface."

It added that AQI will go back to poor by tonight for three days. "Boundary layer has started to go up slowly providing more space for vertical mixing. Still many Met factors are unfavourable and moderate fog will prevail to help both gaseous and particulate pollutants to hang near the surface and delay in faster relief."

Vertical mixing in the room that is available for pollutants to disperse. Surface wind speeds had come down over the past three days and the mixing height or room available for vertical dispersion had come down as well. It was as low as 50m for a few hours on Monday and had resulted in stagnation of pollutants.