Thread: How does smell travel?

So a person with a professional nose can not smell an odor any quicker then my plain old nose in a perfectly calm gym?

Originally Posted by Wolf50

So a person with a professional nose can not smell an odor any quicker then my plain old nose in a perfectly calm gym?

A professional nose?

The olfactory nerves and receptors vary person by person.
Some people have a relatively poor sense of smell compared with other people. Just as aural or visual acuity has some slight variation.

So, quicker, in this case, would be whether he has a more sensitive nose than you do and his receptors in his nose send the signal to his brain before yours does.

Originally Posted by MisterMe

Absolutely not. Absent a driving force, air moves extremely slowly. Because the cigar lighter heats the air, the hot air will rise until it reaches ambient temperature. But, in terms of moving about the building, it will not. If the building is unoccupied with the HVAC turned off, then the odor of the cigar will remain localized in the same spot for days if not weeks.

Incorrect. While the air itself moves slowly, air molecules are bouncing around with great velocity. The air mass as a whole might take a few minutes to move through a room, but the individual scent molecules can permeate a room in seconds.

Originally Posted by mugaliens

Incorrect. While the air itself moves slowly, air molecules are bouncing around with great velocity. The air mass as a whole might take a few minutes to move through a room, but the individual scent molecules can permeate a room in seconds.

Nonsense. The molecules that comprise the odor are carried along with the air mass which you appear to concede moves very slowly. In the absence of a driving force, the odor molecules must diffuse into the surrounding air.

One is left to infer that you believe that individual odor molecules are able to travel at great speed for long distances within a closed room. This could not be further from the truth. The distance traveled by a molecule before it collide with another molecule is characterized by the mean free path. The mean free path of ambient air molecules is 68 nm. By way of comparison, this is about 1/10 the wavelength of red light.

Originally Posted by MisterMe

Nonsense. The molecules that comprise the odor are carried along with the air mass which you appear to concede moves very slowly. In the absence of a driving force...

It's not nonsense. It's science. The driving force is Brownian motion, which carries odors through the air faster than the movement of the air mass itself. My first introduction to Brownian motion was in the third grade. It took five seconds for an odor released up front to reach the opposite corner of the classroom (50 ft distant), but the air circulation (no A/C back in those days) was not moving at 10 ft/s.

Do the math, infer what you will. I'm sticking with the science.

I think your both right for the most part, but side more with misterme.

An aromatic compound by definition has a benzene ring right? That has a molecular weight of what, C6H5+whatever smelly substituent. Thats what, 77 + substituent. Oxygen gas weigths 32 and nitrogen 28. So aside from basic diffusion I don't see why the heavier compound would travel so fast from the source without something propelling it. Althought I could also see it something like a dump truck driving through a honda.

Your basically measuring gas diffusion.

Odour travels by molecules moving in air. It isn't "smell" until it is in the nostrils, and the it travels by nerve impulse. But the frequency of molecular vibrations is quite different to the frequency transmitted to the brain.

Originally Posted by JFalz1024

So aside from basic diffusion I don't see why the heavier compound would travel so fast from the source without something propelling it. Althought I could also see it something like a dump truck driving through a honda.

Your basically measuring gas diffusion.

Right. Mugs seems to have the right idea about that.

Or, he did, months ago.

Originally Posted by grapes

Right. Mugs seems to have the right idea about that.

Or, he did, months ago.

Better late then never