Leaves less polluting van in York (8)
I believe the answer is:
greenery
'leaves' is the definition.
(I've seen this before)
'less polluting van in york' is the wordplay.
'less polluting' becomes 'greener' (green can mean good for the environment).
'van in' suggests taking the first letters (van can mean the front of something).
The initial letter of 'york' is 'y'.
'greener'+'y'='GREENERY'
(Other definitions for greenery that I've seen before include "Colourful display" , "Foliage etc" , "Leaves, maybe" , "Trees" , "colourful stuff?" .)