Originally Posted by FidelCastrovich

I was told and have read that none of the masks do anything against the real nasty pollution, i.e. diesel fumes. Diesel engines emit ultrafine sub-micron particles that none of the usual countermeasures can keep from getting to your lungs. And those particles are the most dangerous by virtue of size and other characteristics.
Respro and the like are good agains dust, smells and the like.