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Your outside the space station in full gear, you open the hatch to enter, space dust enters with you into the airlock as there is lots of dust orbiting the earth, when air is pumped into the lock and you remove the suit, you can then smell anything that may have come in with you. Presuming the particals have an odor.
And I'll have you know, my beard would NEVER catch things and bring them in.
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*Glares at Taw*