Gas shipment not carbon neutral (5)
I believe the answer is:
argon
'gas' is the definition.
(argon is a gas)
'shipment not carbon neutral' is the wordplay.
'shipment' becomes 'cargo' (synonyms).
'not' suggests deleting specific letters.
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'neutral' becomes 'N' (abbreviation in electronics).
'cargo' with 'c' taken away is 'argo'.
'argo'+'n'='ARGON'
(Other definitions for argon that I've seen before include "Organ (anag.)" , "Gas used in electric lights" , "Noble gas, Ar" , "Noble gas, atomic number 18" , "An insert gas to groan about" .)