Polluted air not helping (6)
I believe the answer is:
ration
'helping' is the definition.
(a ration is a serving or helping)
'polluted air not' is the wordplay.
'polluted' indicates an anagram.
'air'+'not'='airnot'
'airnot' anagrammed gives 'RATION'.
(Other definitions for ration that I've seen before include "Quota" , "Share or allotment, of food say" , "Food allowance" , "Limited allocation of food etc in wartime" , "Parcel out scarce food, say" .)