system
Given the following post, respond as if you're commenting on Reddit:
human
If a substance of any kind gives off an odor then does that mean it's losing mass even if it's on a very small scale?

Example -- If I have a container of poop and open the lid I start to smell poop. So my thinking is that if it smells like poop then it must have been a part of the substance in the container but is no more and free to roam about the air I breathe. So the original substance it came from must be lighter in weight because some of it is free and allowing me to smell it.
gpt
Yes, this is exactly how smell works.  Part of the substance volatilizes into the air and those molecules hit receptors in your nose and give smell signals.  That means the substance itself is losing mass.

It should also be noted that generally this is small enough to be incredibly hard to notice.  We can detect very low concentrations of many substances in the air and gas is pretty diffuse compared to a solid or liquid to begin with, which means that only very little of that substance needs to come off. 

Also, for complex things like organics it isn't necessarily all of the stuff that is coming off, just certain compounds.  This means that over time those compounds may deplete and you will be left with something that doesn't smell anymore.