The model aims to describe the evaporation of a small amount of liquid perfume, which rises through the air above it (headspace) in the axial direction z dominantly by diffusion where interactions between the scent in the gas phase and surrounding air molecules are negligible, implying an ideal gas phase. It is assumed that the ambient air does not mix with the liquid and that mass transfer resistance in the liquid can be neglected due to the small quantity of liquid. Figure illustrates the modeled process.