Subjunctive mood - what is the tense of the verb following a conjunction?

Which verb is correct?

If the world were perfect, workers would wear respirators even when dust levels were/are low.

"If the world were perfect" is an impossible condition/situation, which makes it subjunctive, correct?

Does the subjunctive mood only refer to a verb or does it refer to an unreal/imaginary/impossible situation? Example:

"If the world were perfect . . ."
vs.
"In a perfect world . . ."