India, Jan. 7 -- Isolated cold day conditions were expected in Delhi on Wednesday, as a shallow fog enveloped the region, the air quality improved to the "poor" zone, and the minimum temperature was two degrees above normal at 8.6degC.

A 24-hour rolling average Air Quality Index (AQI) of 300 (poor) was recorded at 9am, compared to 310 (very poor) at 4pm on Tuesday. The AQI was expected to be "very poor" until Friday.

On Tuesday, Safdarjung, Delhi's representative weather observatory, recorded a maximum temperature of 15.7degC, three degrees below normal, and Palam 13degC. At least two stations logged cold day conditions on Tuesday as the mercury plunged to 7.6degC.

A "cold day" is when the minimum temperature is below 10degC and its de...