'emission-free' originates from the combination of 'emission' and 'free', where 'emission' refers to the act of releasing something, especially gas or radiation, and 'free' means without or lacking.

'Emission' comes from the Latin word 'emissionem', meaning 'a sending out', and 'free' from the Old English 'freo', meaning 'not in bondage'.

Initially, 'emission' referred to any kind of release, but in modern usage, it often refers to pollutants. 'Free' has maintained its meaning of 'without'.