Round mass in pipe irked one? Smoker here blew top! (7)
I believe the answer is:
pompeii
'smoker here blew top' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'round mass in pipe irked one?' is the wordplay.
I cannot quite see how this works, but
'round' could be 'o' (round can mean a round object) and 'o' is present in the answer.
'mass' could be 'm' (symbol used in Physics e.g. f=ma) and 'm' is found in the answer.
an anagram of 'pipe' is 'ppei' which is within the remaining letters.
'one?' could be 'i' (Roman numeral) and 'i' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pompeii that I've seen before include "Ruined Roman town" , "Buried Roman city" , "Ancient city in Italy" , "Former city" , "Ancient city near Naples destroyed by volcano" .)