Perfumers group notes according to their relative volatility or persistence. The most persistent odors are base notes. The least persistent odors are top notes. Odorants with medium volatility are called middle notes or modifiers. When perfume is placed on the skin, the first scent smelled is the top note.
Base notes remain long after the top notes have faded.
Likely Grouping of Manure Odor Notes Based on Relative Volatility of Odorants. Dust borne odorants Farmstead odors are also chords of many notes. Odorants in the manure chord can be grouped in notes based on relative volatility. Table 3 classifies common manure odorants into top, middle, and base notes. Knowing that all notes do not have the same persistence can explain why the strength of farmstead odors changes over time.