Measure a country's emission (9)

I believe the answer is:

emanation

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'emission' is the definition.
(I know that emission can be written as emanation)

'measure a country's' is the wordplay.
'measure' becomes 'ema' (I can't explain this - if you can you should believe this answer much more).
'a country' becomes 'nation' ('nation' can be a synonym of 'country').
'ema'+'nation'='EMANATION'

Can you help me to learn more?

(Other definitions for emanation that I've seen before include "Issue" , "Something issuing from a source" , "Something given off" , "Pouring out" , "produce radioactive gas" .)

I've seen this clue in the Sydney Morning Herald.

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