No vijesh this is not fog, but Smog which is created by smoke arises from burning of old crops so that new crops could be sown. Happens extensively around Delhi/NCR in the farms of Haryana, UP and Punjab when farmers fire their fields in order to completely destroy the remains of the going season's leftover and then when the fields are burnt completely they are ready to use for the next season.
This happens every year in the months of Oct-Nov and march/April.