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When we spray perfume into the air, we smell the particles of the perfume. Are those particles a liquid or a gas?

Some of us think that it is small, minute droplets of perfume liquid (like steam is condensed water vapor in the form of liquid.

Some of us think that since the perfume is volatile, that the particles that we are smelling are gas particles that have evaporated from the liquid perfume.

Could you please help us with this?

Also, how about the popcorn smell we smell when we microwave popcorn?

Thank you very much!!
Question Date: 2012-05-22
Answer 1:

Odors are caused by small, volatile compounds that trigger olfactory receptors in your nose. The molecules that cause scents can usually be detected in extremely small concentrations, down to parts per billion (ppb).

When you smell perfume on a person or by wafting perfume from a bottle, you are smelling a vapor of the scent compounds that have become volatilized (are in the gas phase) and diffuse through the air and into your nose.

Perfume is a mixture of fragrant oils in an ethanol/water solvent. When you spray perfume, you create a fine mist of perfume droplets suspended in the air. The droplets are usually between 30 and 150 micrometers in diameter depending on the sprayer used. The ethanol/water mixture, which is volatile, evaporates from the droplets within a few seconds, leaving behind a droplet of the fragrant compounds in the perfume. These compounds will also eventually evaporate to form a vapor of the fragrant molecules.* The vapor diffuses through the air, spreading the scent.

Whether you are smelling the droplets or the vapor probably depends on when you spray the perfume. If you smell the perfume immediately after spraying it, you are most likely smelling the droplets. If you smell it from across the room after someone sprays it, you are probably smelling the vapor. How quickly the transition occurs depends on the ethanol/water concentration as well as which fragrance molecules are present in the perfume and their vapor pressures.

When you smell popcorn from the microwave, you are smelling the vapor of popcorn scent molecules (e.g. 6-Acetyl-2,3,4,5- tetrahydropyridine from the popcorn itself and diacetyl and acetoin from the butter). Heating the popcorn volatilizes the scent molecules and they diffuse into your nose.

*Most likely this process is not quite as well-defined as I have described it and some of the scent molecules will evaporate as the ethanol/water mixture does.

References:
James F. Davies, Allen E. Haddrell & Jonathan P. Reid (2012): Time-Resolved Measurements of the Evaporation of Volatile Components from Single Aerosol Droplets, Aerosol Science and Technology, 46:6, 666-677.

Rowe, David J. "Chapter 13." Chemistry and Technology of Flavors and Fragrances. Oxford: Blackwell, 2005. Print. Accessed at Blackwell
pop corn and butter
diac etyl
aceto in
spray bottle
atomizer nozzle
aroma compound

Answer 2:

I like your question. It's interesting to think about.

I think I'm going to have to agree with both sides. Certainly the perfume spray has tiny droplets that you could breathe in, and they would land on the smell receptors in your nose. But then I did some search for: perfume spray gas liquid.

One of the answers talked about how you can rub perfume on your arm and smell it. So that perfume would be coming to your nose as gas molecules, because it would be too hard for tiny water droplets to leap off your arm and into the air!

The popcorn question is interesting, too. I was wondering if the popcorn smell comes mainly in the steam from the popcorn. But then I remembered a chemical I worked with when I did undergraduate research long, long ago. It was a solid, and it smelled like popcorn. Since it was a solid, it wasn't getting to my nose in water droplets, so some of the molecules must have been evaporating from the solid, to reach my nose as a gas.

The bottle of the chemical said, "No physiological effect", or something like that. My professor said the chemical DID have a physiological effect, because Smell was a physiological effect!

This is the best answer I can give you now. Scientists will discover things that might change these answers. For example, I learned that steam was the gas form of water, but now we know that steam is tiny droplets of liquid water. Water vapor is the gas form.

Keep asking questions!
Best wishes,



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