Most scents are mixtures of 100's or 1000's of different chemicals. Since each substance has a different mass, they will diffuse into the air at different rates, with some of the heavier compounds 'sinking' down and the more volatile aerosolizing right away. Without gravity, denser compounds can get to the surface just as easily as the lighter, thus altering the spectrum of chemicals that we percieve as scent.

Has anyone come across a reason (or theory) why scents would
change in space?