New Delhi, Jan. 4 -- A day after strong surface winds improved Delhi's air quality by more than 100 points, prompting revocation of impositions under Stage-3 of the Graded Response Action Plan (Grap) to curb pollution, the city's air quality index (AQI) once again started slipping towards the "very poor" category. Shallow to moderate fog was also a contributing factor, which led to more than 60 flight cancellations at the Delhi airport. The India Meteorological Department (IMD) has also issued a yellow alert for today, warning people of a possible moderate to dense fog in multiple parts of the city. "A yellow alert has been issued for Sunday. According to the Central Pollution Control Board's (CPCB's) daily bulletin, Delhi recorded an AQI of 236 at 4pm on Friday. Noida on the other hand, recorded an AQI of 211 on Friday. Meanwhile, Greater Noida recorded an AQI of 232 and Ghaziabad had an AQI of 220. On Saturday, at 4pm, Noida recorded an AQI of 332, which comes under the "very poor" category, followed by Greater Noida at 334 and Ghaziabad at 309. Mahesh Palawat, vice president at Skymet, said, "The wind speed was around 7-8 kmph throughout the day on Saturday, with wind conditions expected to remain the same over the next two days." According to forecasts by the Air Quality Early Warning System (AQEWS) for Delhi, the air quality is likely to be back in the very poor category by Sunday. "The air quality is likely to be in the very poor category from Sunday to Tuesday. The outlook for the subsequent six days is that the air quality is likely to be in the very poor category," said the AQEWS bulletin on Saturday evening. The CPCB classifies air quality as "moderate" when the AQI is between 101 and 200, "poor" between 201 and 300, and "very poor" between 301 and 400. Beyond 400, air quality is termed "severe". According to airport officials, 34 arrivals and 38 departures were cancelled at the Delhi airport. The flight tracking website FlightRadar24 showed that over 500 flights were delayed. Airport officials said the cancellations and delays were predominantly due to the impact at other airports, including several in northern India, where visibility was severely affected. Airlines have been posting on their social media handles, requesting passengers to check for updates. The minimum temperature on Saturday was recorded at 8 degrees Celsius (degC) , which was 1.2degC above normal. The maximum on the day was logged at 17.3degC, two degrees below normal....