A question about structure

Dear great people!
Could you please help me with this sentence?
Carbon dioxide may be absorbed by trees or water bodies, or it may stay in the atmosphere when ______, while it is only in the atmosphere that chlorofluorocarbons find their home.

1. by releasing emissions from cars B. released from car emissions

C. cars that release emissions D. emissions are released by cars
I do know that we omit “A & C” because after when we should use:
When + Subject + Verb, i.e. When he was a child, he used to cry a lot.
When + Noun (reduced form, i.e. When a child, he used to swim in this river.)
When + V –ing (“when” here is used as a preposition)
When + past participle (reduced form): i.e. When used wisely= when it is used), money can do a lot of things.
The answer is B. released from car emissions. i.e.:
Carbon dioxide may be absorbed by trees or water bodies, or it may stay in the atmosphere when it (= Carbon dioxide) is released from car emissions, while it is only in the atmosphere that chlorofluorocarbons find their home.
My question is that “why not “D. emissions are released by cars.” What’s wrong with it?
I’ll greatly appreciate your detailed answer.
Thanks in advance.