What does the phrase 'in the open air' mean?

[Ronana]

Test No. incompl/advan-28 "Mistaken Identity", question 2

Candidate: I think the main reason is because I like working in ..........

(a) the free air
(b) the clear air
(c) the pure air
(d) the open air

Test No. incompl/advan-28 "Mistaken Identity", answer 2

Candidate: I think the main reason is because I like working in the open air.

Correct answer: (d) the open air

Your answer was: correct
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It was a nice little dialogue.
However, I wanted to ask whether "open air" doesn't only mean here working "outside" but working "in good/clean/healthy air", too?

As it seems "clear air" is not suitable.

[Alan]

This means quite simply outside in contrast to inside.
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