my thought is that it would be much too hot to wear one in the summer and would probably restrict breathing. i've also read that they don't actually filter out any of the really harmfull airborne toxins. i've been experimenting with herbal supliments the past few years that aid in cleansing the respritory system. to that end i take nettle leaf suppliments. nettle is a air purifying plant that you often see growning next to highways for this very purpose (it grows like a weed). don't ask me how if works but all i know is i'm clearing my throad a lot less during the summer. could be the placebo effect, but then again so is the mask.

EDIT: duh, i wrong herb. i was thinking about Mullein leaf. Nettle is for seasonal allergies.