|MadSci Network: Biophysics|
Dear User, Scents are carried through air by diffusion and by convection. Convection is movement of the air itself, as a medium and is much faster than diffusion, normally. I assume that you refer to travel of scent through still air, which is governed by diffusion. Diffusion rates depend on several variables, including the concentration of the molecules at the starting point and the type (and size) of the molecule itself. Air molecules whizz around very fast (around the speeds of rifle bullets, on the average). When you have a higher-than-average concentration of something in the air, the molecular motion will eventually spread the substance around until it is uniformly mixed. Larger molecules move slowly, smaller molecules move faster. The larger the gradient of concentration, the sooner the concentration of the scent molecules will reach the threshold of detection. This is another factor, but a more subjective one. Different substances have different detection thresholds by human nose, so some things may *seem* to travel faster whereas they simply are detected earlier. In general it is a safe approximation that the smaller the molecule, the faster it travels. Aerosol air freshners usually do not directly counteract vile smells. They simply overload your nose and it becomes relatively insensitive to unpleasant smells. Some aerosols in addition have substances which "capture" smelly molecules in the aerosol drops. If you would like to read more on diffusion, I suggest to start with Einsteinian models which are described in any semi-decent advanced physics textbook. Cheers, A.G.E. P.S. Or try this link to Brownian diffusion for a little more information http://www.foresight.org/Nanomedicine/Ch03_1.html Bill Reisdorf, Biophysics moderator
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