Millipore filters needed to filter out bacteria and viruses will not allow enough air to pass through quickly enough to be of any service since it would take too long for the air in the entire cabin to be filtered. In the mean time, you would be breathing unfiltered air combined with little amount of filtered air which completely defeats the purpose. You could ,however, feign oxgen deprivation and ask that your oxygen mask be dropped and then you can breathe pure air, just don't breathe too fast, the O2 content is higher than the atmosphere.
It is filtered. Usually at .5 microns.