Heavy Dense Fog In Delhi/NCR

NEW DELHI, INDIA - JANUARY 8: Many trains run late due to heavy fog, at Tilak Bridge Railway Station, on January 8, 2016 in New Delhi, India. Dense fog blanketed many areas in and around Delhi this morning with poor visibility affecting over 100 flights and hitting road traffic in rush hour. Fog is formed when temperatures are low, humidity is high, wind speed is low and the level of pollutants in the air is high. Recently, a scientist linked the formation of fog to the presence of particulate matter 10 in the air. Analysing data for the past two months, he found that PM 10 concentration was high on days of heavy fog. (Photo by Arvind Yadav/Hindustan Times via Getty Images)