I have noticed that after wearing a respirator (dual-cartridge activated charcoal by 3M) for an hour or so, when I remove it, the ambient air smells slightly sweet, almost like slight hint of ozone. After a little while without it, the smell seems to "go back to neutral" or nothing unique. I realize there is ozone in the air, but am surprised it'd be enough to smell, and it may not be ozone at all. However, I am assuming it is some kind of an "old-nose" type of thing, the respirator blocks all odors for an extended period, and then I am suddenly exposed to it again... maybe? Anyone have any ideas?