The famous description of the fog that is reported to us at the beginning of this excellent Dickensian classic seems to function as a way of pointing out the various sinister, evil and corrupting forces that lay upon the city of London just as the fog itself seems to form something of a shroud that covers every aspect of life. The fog is explicitly linked with pollution, as it rolls down the river, "where it rolls defiled among the tiers of shipping and the waterside pollutions of a great (and dirty) city. However, the fog is also personified as a cruel person, as the following quote demonstrates:
...fog cruelly pinching the toes and fingers of his shivering little 'prentice boy on deck.
The way in which Dickens personifies the fog thus only helps build up this picture of the fog being an evil presence that is testament of the malign set of virtues and values that he has already written about in the Preface to this novel that draws attention to the injustices of the Chancery and how this is a dog-eat-dog world of no pity or hope.