Pure air is colorless and tasteless. If you smell it, take the fragrance of flowers as an example. It is not necessarily that pollen has entered the nasal mucosa. It is more likely that some chemical substance has evaporated. To be precise, many plants contain a chemical called "aromatic hydrocarbon" in their flowers (it is a chemical with benzene ring structure, so it is called aromatic hydrocarbon because it is extracted from plants), and plants will emit aromatic hydrocarbons, which will float in the air.

In fact, this "smell" (fragrance) is just a nerve stimulus, not a physical substance.

But it's the chemicals that cause the stimulation.

Take a flower as an example, because it is a complex organism. If you smell it, it may just be that its secretions have evaporated. It can't be said that "flowers" are volatile.

But if it is a bottle of vinegar, you can smell it. That's because acetic acid molecules volatilize into the air and you inhale. This is called "acetic acid" transfer. It is worth noting that vinegar is "a mixture of acetic acid, water and other chemicals". Can't say "vinegar" transfer, can only say "acetic acid" transfer. More and more details are not convenient to say.