In New York, occasionally passata is unpleasant (5)
I believe the answer is:
nasty
'unpleasant' is the definition.
(nasty can mean unpleasant or horrible)
'in new york occasionally passata' is the wordplay.
'in' means one lot of letters goes inside another.
'new york' becomes 'ny'.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'passata' are 'ast'.
'ny' enclosing 'ast' is 'NASTY'.
'is' acts as a link.
(Other definitions for nasty that I've seen before include "grave" , "Horrible" , "Evil" , "Highly repugnant" , "Obscene" .)