Concerned with smell round large manufacturing plant (9)
I believe the answer is:
olfactory
'concerned with smell' is the definition.
(I've seen this before)
'round large manufacturing plant' is the wordplay.
'round' becomes 'o' (o is a circular letter).
'large' becomes 'L' (eg in clothes sizes).
'manufacturing plant' becomes 'factory' (synonyms).
'o'+'l'+'factory'='OLFACTORY'
(Other definitions for olfactory that I've seen before include "Pertaining to the sense of smell" , "associated with a stink" , "Detecting scent" , "Dealing with smells" , "concerned with smell" .)