Though Paste of the Spirits is sometimes held to be the opposite of the Noble Spices, they also have a naturally-occuring antithesis: miasma, more commonly known as 'foul air' or 'bad air'.
Miasma is a gas formed when air mixes with the breath of poisonous animals or decaying cadavers. It is invisible, but may have an odor (which, if present, is always unpleasant). In other respects it is, unfortunately, indistinguishable from air. Unfortunately, because miasma is entirely harmful, causing sickness and death to whatever it touches.
The formation of Hollow Mockeries is a specific case of the action of miasma. Other, more common examples are the illnesses suffered by those who spend too much time in a swamp or in close proximity to corpses. Some have suggested that the curse that falls on anyone who robs a corpse is not in fact caused by vengeful spirits, but is the natural action of miasma.
Burning the Noble Spices will purify the air - although miasma is very cunning, and may flee the purifying fumes, to return when they have dispersed. Holding them to one's nose, for example in a handkerchief, will purify the air that is breathed in. However some forms of miasma may cause sickness upon contact with the skin. The essence that arises from old books is more effective (which is why librarians and the owners of second-hand bookshops tend to be incredibly old).
So-called Miasma Elementals are Air Elementals that have been corrupted by miasma.
(my thanks to M. Grognard, upon whose research I have drawn in preparing this entry)