[rckoepke]

HEPA filters are actually more efficient at capturing very very small particles (<0.1 micron) than they are at capturing simply small particles (≈0.3 micron). The tiniest particles are light enough to be captured using electrostatic forces rather than the more typical mechanical filtration that is effective at capturing large particles.

More precisely, many odors are not particles at all but rather gases/vapors. Activated charcoal can capture larger organic molecules because it has an incredibly jagged/porous surface - just 100 grams of activated charcoal provides over 1,000,000 square feet of "effective" filtration surface area.

[cyounkins]

Yes, that's true that HEPA is very efficient at particles in the 0.01 to 0.1 micron range. It may also be below that, but I personally haven't seen that data. But because HEPA fails to filter gases/vapors, its performance must fall off before 1 angstrom = 0.0001 micron.

> odors are not particles at all but rather gases/vapors

I think the confusion comes from people referring to "particulate" as particles of >= 0.01 micron, whereas in physics we say that gases/vapors are also composed of particles. They may be single atoms floating (can't actually come up with an example though) or small molecules like O^2, CO, etc, but I'd still call those particles.

[ClumsyPilot]

> 'but I'd still call those particles'

But then in your world there are no such things as gasses? If so, the world uses all usefullness