The problem I find with airborn pollutants is that you never know when and where you will encounter them.
Even a person wearing deodorant sitting near you on a bus is enough to make breathing difficult.
Taxis with those impregnated cardboard air 'fresheners' are the worst because the scent is confined in a small space.
I have found an (expensive) solution to the problem
Wein Air Supply Mini-Mate Wearable Air Purifier
The Home of Mini-Mate in Europe - reduce exposure to swine flu
I never leave home without it.