New Delhi, Jan 6 (IANS): After showing slight improvement on Friday, Delhi's air quality deteriorated again to the 'severe' category on Saturday due to unfavourable meteorological conditions.

As per Central Pollution Control Board (CPCB), the overall air quality index (AQI) on Saturday dropped to 407 at 4 p.m, against Friday's 'very poor' condition at 386.

In the National Capital Region (NCR), Faridabad at 415, Ghaziabad at 417, Greater Noida at 414, Gurugram at 404, and Noida 403 also fared in the 'severe' zone.

Across 35 areas in Delhi, where pollution is actively monitored, the average concentration of PM2.5 and PM10 was 266 and 417 microgrammes per cubic meters on Friday at 5 p.m.

The same PM2.5 and PM10 concentration across 48 monitoring stations in the NCR was 250 and 394.

Delhi's air quality had slightly improved on Friday due to good wind speed but contrary to the forecast, unfavourable conditions like fog and cold have again turned it severe.

However, rainfall forecast for Saturday and Sunday might improve the conditions. "Only sufficient amount of rain could rapidly improve the situation, light rain will only worsen the situation," said System of Air Quality and Weather Forecasting And Research (SAFAR).

The agency has also forecast "moderate foggy conditions" during the next two days over Delhi and surrounding regions which may not allow significant improvement in the air quality.

During the last 24 hours, marginal change in minimum temperatures was observed over the entire Delhi region. Shallow to moderate fog was observed during morning hours, with the lowest visibility reported at Palam at 200 metres and Safdarjung observed 500 metres, private weather forecaster Skymet said.