John did an excellent job. I've worked as an industrial x-ray tech in the petro chemical industry where I had to have evaluation and fit test for resperators and yes you would have to be really paranoid about pollutants (or eviromentally sensitive) to go that route but it is likely the most effective way. You do have to be clean shaven for the resperator to be effective and leak free and one fit test is not for a lifetime. You need to do fit tests over because your face changes.

SCBA (self contained breathing apperatus) is in practical due to smaller (known as escape units) only hold 5 minutes of air while larger units are heavy and with higher levels of physical work (like riding a bicycle) you will find the air tank empty sooner.

As for the commercial units sold to the general public I don't think they will be too effective because they don't take some of the above conciderations into account