Wrong engaging in vehicular sex in green belt? (6,4)

I believe the answer is:

carbon sink

I'm a little stuck... Click here to teach me more about this clue!

'engaging in vehicular sex in green belt?' is the definition.
I know nothing about this answer so I can't judge whether this works.

'wrong' is the wordplay.
I cannot really see how this works, but
'wrong' could be 'sin' (wrong can mean a sin or crime) and 'sin' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Guardian.

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