It emerges as a key assignment (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
emission
'it emerges' is the definition.
The definition suggests a singular noun which matches the answer.
'a key assignment' is the wordplay.
'a key' becomes 'E' (a musical key).
'assignment' becomes 'mission' (mission is a kind of assignment).
'e'+'mission'='EMISSION'
'as' acts as a link.
Can you help me to learn more?
(Other definitions for emission that I've seen before include "Release" , "Something given out" , "Process of giving out" , "issue" , "Going out" .)