NEW DELHI: Delhi recorded poor air quality on Thursday for the first time this season, the Central Pollution Control Board said.

The Air Quality Index, based on 33 air quality monitoring centres, was at 211. AQI between 201 to 300 is considered as poor.

Indications of increased fire activity during the last 48 hours are visible from satellite imagery and further deterioration of AQI is expected for the next two days, the CPCB said.

According to System of Air Quality and Weather Forecasting And Research (SAFAR), the southwest monsoon has withdrawn from northwestern parts of the country and conditions are becoming favourable for further withdrawal from parts of northwest India and adjoining central India during the next four to five days.

The late monsoon withdrawal is not good for air quality in north India, it said.

"During the 3rd to 4th week of October, the temperature will also start to cool. The anticyclone, which persists as part of the withdrawal, associated with clear skies and sinking motion will make the atmosphere very stable beneath means significantly calm surface winds," SAFAR said.

Both will lead to stagnant weather conditions like low wind speeds, descending air and compressed boundary layer, which favour rapid fine particulate matter formation and accumulation of pollutants.

It said the situation becomes bad if it is encountered with any additional internal (firecrackers) or external (stubble burning) emission source.

"In a landlocked city like Delhi, it may lead to rapid accumulation and may trigger high pollution events.

However, if local emissions are controlled it will be a good check to observe and avoid air quality crises," it added.