Delhi saw a moderately smoggy Monday morning with the minimum temperature at 12.4 degrees Celsius, a notch below the season's average.
At least 69 trains were delayed, 22 rescheduled and eight trains were cancelled due to the shallow fog in northern India.
"The sky will remain mainly clear during the day with moderate fog in the morning," the India Meteorological Department (IMD) said.
Humidity at 8.30 am was 93 per cent and visibility was 400 metres.
The Rejandra Nagar Terminal-New Delhi Sampoorna Kranti Express was delayed by over 24 hours while the Sitamarhi-Anand Vihar Lichavi Express was delayed by over 25 hours.
The cancelled trains include -- New Delhi-Varanasi Mahanama Express, Delhi-Azamgarh Kaifiyat Express, Anand Vihar-Mau Express, Sriganganagar-Delhi Intercity, Delhi-Fazlika Intercity, Delhi-Alipurdwar Mahananda Express and Raxual-Delhi Sadbhawana Express.
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According to the Delhi International Airport Limited (DIAL), no flights were delayed or cancelled.
Sunday's maximum temperature settled at 28.4 degrees Celsius, the season's average, while the minimum was 13 degrees Celsius, a notch below the season's average.