Crossword Genius

Cleaner air can't be found here (6)

Ross

I believe the answer is:

vacuum

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'cleaner' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

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(Other definitions for vacuum that I've seen before include "Emptiness" , "Area empty of matter" , "A region empty of matter" , "Space entirely devoid of matter" , "Space empty of matter" .)

I've seen this clue in The Globe and Mail.
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