Heading north, look angry with a fog? (7)
I believe the answer is:
aerosol
'fog?' is the definition.
(fog is a kind of aerosol)
'heading north look angry with a' is the wordplay.
'heading north' says the letters should be written backwards.
'look' becomes 'lo'.
'angry' becomes 'sore' ('sore' can be similar in meaning to 'angry'**).
'with' is a charade indicator (letters next to each other).
'lo'+'sore'='losore'
'losore' reversed gives 'erosol'.
'erosol' after 'a' is 'AEROSOL'.
(Other definitions for aerosol that I've seen before include "Air spray" , "Sprayer" , "What makes mist" , "air-freshener possibly required" , "source of graffiti?" .)