What I recommend people [in airplanes] do is turn the overhead air releaser on to a low stream and position it so the flow goes in front of your face. That will increase the ventilation, at minimal, create a turbulence of air in front of your face. If a particle is coming by, that might be enough to push it out of the way.
M. Gendreau, Tufts University & Lahey Clinic
in When Flu Flies (Newsweek) April 27, 2009