Box of smoke

[Tom Mazanec]

I seal up a puff of tobacco smoke in an airtight box and leave it alone.
Does the smoke settle out like hyperfine dust?
Does it stay in suspension like gas molecules?
Something else?

[cjameshuff]

I seal up a puff of tobacco smoke in an airtight box and leave it alone.
Does the smoke settle out like hyperfine dust?
Does it stay in suspension like gas molecules?
Something else?

Smoke is a complex mixture that can contain solids, liquids, and gases. Some of the particulates may be fine enough to be kept suspended by brownian motion, others will settle, and others will adhere to any surface they encounter. Some of the liquids may evaporate, some of the gases may condense. Some of the components are likely to be unstable or reactive, and will oxidize or polymerize over time, or react with other components.

With tobacco smoke, I expect you'd eventually end up with all surfaces coated with a film of soot, ash, and tar, the remainder being nitrogen, CO2, maybe CO, and various volatile organic compounds.

[Spacedude]

"With tobacco smoke, I expect you'd eventually end up with all surfaces coated with a film of soot, ash, and tar, the remainder being nitrogen, CO2, maybe CO, and various volatile organic compounds."

When my chain smoker aunt died 20 years ago we had to scrub down all the walls in the house before repainting them to sell it. This was immediately realized when we first applied white paint which turned into a yellowish/brown paint job in the process.

[Trebuchet]

Supposedly airplane mechanics used to be able to find cracks in the skin because of the nicotine stains!

[grant hutchison]

You never did this experiment as a kid?
Hold a wide transparent tube over a smoky source (we burned newspaper, and used a tube that had contained some golf balls, I think). Seal the top, then the bottom.
Wait.
Within an hour the visible smoke is a brown-grey deposit on the walls of the tube. (Presumably some gaseous combustion products and very fine particulates remain in the air, but what we'd call "smoke" is gone.

Grant Hutchison

[DaveC426913]

We bought a house occupied by a smoker of decades.
When they moved out they took their wall paintings.
We were left with walls with "windows" made of un-nicotine-stained wall.

[grant hutchison]

When they moved out they took their wall paintings.

Hmmmm. Another for the "two nations divided by a common language" list, I think. If someone took their wall paintings out of a house in the UK, they'd have chiselled off a mural.

Grant Hutchison

[Noclevername]

Hmmmm. Another for the "two nations divided by a common language" list, I think. If someone took their wall paintings out of a house in the UK, they'd have chiselled off a mural.

Grant Hutchison

That would explain the color change.

[kzb]

There will be a certain particle size (and mass) below which Brownian motion will keep it suspended indefinitely.

But if the particles interact with each other -clumping in growing in size - they will eventually settle out. This is what is seen in clouds and fog, the water particles remain suspended until they join together into larger drops.

[Tom Mazanec]

Interesting, kzb.
Do you know the size for room temperature air?

[CJSF]

Hmmmm. Another for the "two nations divided by a common language" list, I think. If someone took their wall paintings out of a house in the UK, they'd have chiselled off a mural.

Grant Hutchison

I dunno. If someone says "wall paintings" to me, I also think actual paint on the walls. For paintings hung ON the walls, I think most of us just call them "paintings" or if a modifier is needed, "paintings hung on the walls".

CJSF

[profloater]

Years of smoking adds patina to busts, objects, paintings which is very difficult to fake. When cleaned, people cry garish! I was lucky to buy some British museum surplus heads with maybe a hundred years ? of patina from tobacco smoke. No odour remained.

[grant hutchison]

I dunno. If someone says "wall paintings" to me, I also think actual paint on the walls. For paintings hung ON the walls, I think most of us just call them "paintings" or if a modifier is needed, "paintings hung on the walls".

Likewise. Framed paintings hung on the wall are just "paintings". Prints would generally be specified as "framed prints", I think, since "removing your prints" from a room conjures images of a crime scene. And more generally we have "wall art", which includes stuff like the flat metal sculpture of a shoal of tropical fish that hangs on the wall in our kitchen.

Grant Hutchison

[kzb]

Interesting, kzb.
Do you know the size for room temperature air?

I can't find a link which explains it, but I am sure I've read this somewhere. After all, heavy gas molecules don't settle out, they just have a smaller scale height.

On the other hand you can find a lot of stuff on Stokes Law:

A 10nm radius water droplet in air at normal temperature falls at 7mm per day in Earth surface gravity. Clearly any small air currents can overwhelm this rate of fall.

[grant hutchison]

Interesting, kzb.
Do you know the size for room temperature air?

But there's huge influence from the walls of the container. While a particle may be small enough to stay suspended by Brownian motion, it will eventually encounter the container wall. At that point, other forces become involved.

Grant Hutchison

[kzb]

Interesting, kzb.
Do you know the size for room temperature air?

No, but the problem is related to Brownian motion and diffusion.

When you think of a particle in a fluid undergoing Brownian motion, at first thought you might think the average position of the particle should not change. After all it is a purely statistical phenomenon, if at some time the particle gets moved right, it should move left with equal probability.

But it does not work like this. There is net diffusion of particles from areas of high concentration to areas of lower concentration. Brownian motion causes a particle to go on a random walk, and with no gravity or other complications, given enough time the smoke particles would end up equally distributed throughout the container volume.

With gravity added, and assuming the particles are denser than the fluid, there is downward movement superimposed on diffusion. At equilibrium, the particles end up more closely spaced at the bottom than at the top. However there are still particles throughout the volume, and any given particle can go on a random walk to the top of the container.

This only works with small and light enough particles, such that Brownian motion is significant compared to their sedimentation rate due to Stokes Law.