I wear face masks for the cold and the one thing I can tell you is that it has to be comfortable and it has to be easy to breathe, or the mask will soon find its' way to the bottom of a drawer somewhere - forgotten.

Also, if it looks too goofy, you won't want to wear it.

In Asia, the old gauze masks are pretty common for bicycle commuters. I am not sure how effective they are for pollution, but I guess it is better than nothing.