New Delhi, Dec 25 : The flight operations at the Delhi airport were normal on Saturday morning despite low visibility due to the fog. "Low visibility procedures are in progress at Delhi Airport. All flight operations are presently normal," the Delhi airport said in a passenger advisory. Low Visibility Procedures are the actions to ensure the safe operation of aircraft during periods of reduced visibility or low cloud base. The airport authorities further requested all passengers to contact the airline concerned for updated flight information. According to the India Meteorological Department, the runway visibility was low in the morning. It further forecast that visibility may reduce to 1200m in mist from 6.00 p.m. and further reduce to 800 m from midnight. Meanwhile, after crossing the 400 or 'severe' mark a day ago, Delhi's Air Quality Index (AQI) improved marginally on Saturday to 398, which is the lower end of the 'very poor' category. "The air quality is likely to improve further but remain in the 'very poor' category on December 25 and 26. The air quality is likely to improve significantly from December 27 when AQI reaches the 'poor/moderate' category," said the air quality and weather bulletin. An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', and between 401 and 500 is considered 'severe'. The level of PM10 and PM2.5 pollutants were recorded in the 'very poor' category, respectively. /IANS