Comments on: Microolfactoryfilter

Question: Microolfactoryfilter

Eiwalker — Sat, 16 Sep 2006 08:32:02 -0800

What's the smallest thing that can be smelled by a human?

Where the human can identify (accurately and reliably) what it is, such as, "Oh, I'm smelling a such-and-such!"

By: Blazecock Pileon

Blazecock Pileon — Sat, 16 Sep 2006 08:34:15 -0800

A molecule that triggers an olfactory receptor. Molecules are pretty small.

By: Aquaman

Aquaman — Sat, 16 Sep 2006 08:36:42 -0800

OK, but what's the LARGEST thing...?

By: bru

bru — Sat, 16 Sep 2006 08:42:06 -0800

Blazecock Pileon: So the question could be: "How many molecules does it take to trigger a conscious perception of smell?", right?

By: caddis

caddis — Sat, 16 Sep 2006 08:54:25 -0800

ethyl mercaptan

By: solotoro

solotoro — Sat, 16 Sep 2006 09:00:08 -0800

Oh, we're going for smallest molecule? Then I submit
hydrogen sulfide

If you're asking what's the smallest amount of material we can smell, then I would think it would depend not only on our molecule-number sensititivity to the compound (and I would think this would be different for different compounds) but also on the ability of the substance in question to vaporize.

Have you looked here?

By: Blazecock Pileon

Blazecock Pileon — Sat, 16 Sep 2006 09:03:36 -0800

So the question could be: "How many molecules does it take to trigger a conscious perception of smell?", right?

Not sure. It could be asked how many receptors need to be triggered in order to send a signal, since the trigger is what registers the perception in the brain, not the odor molecules themselves. It could well be said that time is another important factor in smell perception.

By: weapons-grade pandemonium

weapons-grade pandemonium — Sat, 16 Sep 2006 10:06:47 -0800

A Connisseur's (sic) Guide.
Should be Connoisseur, but a worthwhile read, especially for the comments.
Has anyone else experienced the olfactory "illusion" of smelling skunk when the first traces of brewing coffee hit your nose? It may be that small amounts of mercaptans in the coffee are the first to register. Weird that a miniscule whiff of something that smells so good can smell bad.

By: auntbunny

auntbunny — Sat, 16 Sep 2006 11:05:40 -0800

One of my favorite books is The Emperor of Scent: A Story of Perfume, Obsession, and the Last Mystery of the Senses by Luca Turin. It is largely about this.
Here's more from here if you're interested.

...auntbunny, who smells like white shoulders and lawn clippings today.

By: nanojath

nanojath — Sat, 16 Sep 2006 14:48:53 -0800

It will vary with the substance in question and the individual. Try googling "odor detection threshold" (odour for the UK/Australian etc. scientists). It is a value that is always expressed as a concentration (generally ppm) and averages are calculated for purposes from perfumery to determining safety guidelines for chemicals.

By: Eiwalker

Eiwalker — Sat, 16 Sep 2006 16:50:53 -0800

Nice responses. Some good candidates, and also the good point that taking a big long whiff makes it easier to smell something than taking a quick little whiff. Similarly, how far away you are from the thing is relevant. I take it that if it were in your nose, that would be ideal. But if the smallest thing we can smell is a raunchy molecule, this rules out smelling a single atom, even if it were in one's nose. But if the smallest thing we can smell is a molecule, how close would we have to be in ordinary circumstances, such as in a 10 x 10 x 10 bedroom, or outdoors in a park? A foot, a meter? Apologies if this information is contained somewhere in one of the previously mentioned links!

By: Eiwalker

Eiwalker — Sat, 16 Sep 2006 17:09:11 -0800

I've suddenly taken an interest in Aquaman's question, "OK, but what's the LARGEST thing...?"

We can smell single molecules, and compounds, but not, I take it, entire countries or houses. What is the approximate limit, anyway? That is, what's approximately the biggest thing we can smell (and identify) with a single big long whiff?

By: plinth

plinth — Sat, 16 Sep 2006 17:09:22 -0800

Proximity matters only in that you can smell something when the molecule collides with a receptor in your nose. At this point you're talking diffusion in the room. The longer it's had time to diffuse or if there is more active air currents than mostly still air, the sooner you'll smell it.

By: caddis

caddis — Sat, 16 Sep 2006 19:19:43 -0800

What is the largest thing?

Have you ever even gotten close to Gary, Indiana?

By: flabdablet

flabdablet — Sat, 16 Sep 2006 22:47:23 -0800

I smell a misapprehension in Eiwalker's second-latest question.

But if the smallest thing we can smell is a molecule, how close would we have to be in ordinary circumstances, such as in a 10 x 10 x 10 bedroom, or outdoors in a park? A foot, a meter?

Smell isn't like sight or hearing, which act at a distance via assorted kinds of wave; smell involves physical contact between molecules originating in the smelly object and receptors in your nose. You can't smell a single molecule at all until it physically docks with a receptor inside your olfactory canal.

If you do perceive a single molecule as a smell, that gives you no information at all about how close you are to the object that molecule was originally part of, except that it was more likely to be far than near. You'll get literally billions of scent molecules up your nose from anything even remotely near you.

By: null terminated

null terminated — Sun, 17 Sep 2006 00:08:02 -0800

This also means that when you can smell a fart you have molecules in your nose that have been in someone else's rear.

The more you know.

By: flabdablet

flabdablet — Sun, 17 Sep 2006 06:02:45 -0800

It's OK. Even if you can't smell a fart you have molecules circulating in your bloodstream that have been in someone else's rear.

It's a chemistry thing, it's a sharing thing, it's a beautiful thing.

By: rmless

rmless — Sun, 17 Sep 2006 13:17:25 -0800

Possibly interesting side note:
A science exhibit I saw once said that the shape of the molecule is more important than the makeup of the molecule itself. So you can arrange a molecule made of other stuff that is shaped and sized like a strawberry molecule and it will smell like strawberries even if there are no actual strawberry molecules there.

By: Eiwalker

Eiwalker — Sun, 17 Sep 2006 14:27:02 -0800

auntbunny had left a link for the Vibration Theory of Olfaction from Wikipedia: http://en.wikipedia.org/wiki/Vibration_theory_of_olfaction

I guess my question of how close you have to be to smell something only makes sense on that model.

Thanks again for the apt comments!

By: flabdablet

flabdablet — Mon, 18 Sep 2006 00:27:29 -0800

Well, no, actually it doesn't. The vibrational theory is about additional requirements for molecules that are already docked with receptors, and doesn't imply smell action at a distance.

Philip Callahan's interesting infrared model for insect pheromone detection doesn't apply to us, because we don't have anything like a working insect antenna; our only way to detect the molecules we perceive as scents is by physically sucking them up.

By: Eiwalker

Eiwalker — Wed, 20 Sep 2006 05:11:32 -0800

I stand corrected again! Thanks again!

By: DevilsAdvocate

DevilsAdvocate — Fri, 22 Sep 2006 17:08:45 -0800

Oh, we're going for smallest molecule? Then I submit
hydrogen sulfide

Hydrogen fluoride would be notably smaller, and apparently has a "strong, irritating odor." But HF is nasty stuff and I have no intention of verifying that personally.