Sensitivity to smell is actually something that I've been thinking about for the last few days, odly enough. I have light and sound sensitivity, but almost no sensitivity to smell. I figured it is due to a sinus surgery I had as a kid that messed my sense of smell up.
As for wearing a mask, finding one that will eleminate organic vapors, as neilson_wheels pointed out, might difficult, if you don't want to attrack a lot of attention while wearing it in public.
I did see an alternative on Youtube a short while ago that you might be interested in. I think it's called thera-putty or something to that effect. It's a kneadable putty with roughly the consistency of playdough which is scented. I think it's ment for stimming but it might help alleviate some of the overpowering negative smells you run in to?
As far as masks goes 3M makes an odor blocking mask that looks more like what you would see someone who is spray painting something wear at right around the $10.00 price range.
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"The only way to live in an un-free world is to become so absolutely free that your very existance is an act of rebelian." - Albert Camus