Lesson 1 of 2 in this stage
Scent transport: diffusion and moving air
Understand why reach changes with the setting rather than forming a fixed-radius sphere.
From source to observer
After release, volatile materials travel through interacting processes. Molecular diffusion results from random molecular motion; bulk airflow carries air and the materials within it. Ventilation, movement and currents make a real room uneven. Someone farther downwind may notice a scent that a closer person elsewhere does not.
Source, environment and observer form three links
What reaches perception depends on release from the source, transport and dilution through air, and the observer's detection. Temperature can affect material release, but no universal rule doubles every perfume's projection at a given temperature. More spray also does not imply proportionally greater reach; transport and perception are not a simple linear ruler.
Projection and trail change over time
Movement can leave scented air behind the wearer, contributing to what is called sillage. Sitting changes airflow, and changing release alters reach over time. A useful report states observation time, movement and ventilation rather than assigning a permanent distance as though printed on the bottle.
Design one experimental question
To explore ventilation, keep perfume, amount and observation time similar and compare suitable settings with consent. Room size and temperature may also differ, so record limitations. Do not use intense exposure in enclosed spaces or expose people without agreement; the aim is understanding use, not saturating the air.
Projection is not a fixed radius around a wearer
Fragrance molecules move through a combination of molecular diffusion, airflow, convection and movement. How far another person notices a scent depends on ventilation, temperature and perception, not molecular size alone. There is no single “projection radius” that applies to every room.
A trial-design scenario
If you assess a perfume near a fan and later in still air, differences do not establish that its chemistry changed. An observer's inability to perceive a smell does not mean no molecules reached them; sensory sensitivity varies. Record setting, distance and airflow rather than treating unlike conditions as directly comparable.
Your turn
Use what you learned
Why should 'Always projects two metres' be qualified?
See the answer and why
Reach depends on time, amount, airflow, setting and observer. Report an observed distance under stated conditions rather than a fixed radius for every use.
Check your understanding
Answer four questions, then review the reason for each answer. You can retry.
Interpret the evidence
Scent transport involves evaporation, convection and diffusion; molecular weight is not a projection meter. Even modest airflow can alter distance-test results substantially.
SESH exercise: choose two scents and record results before viewing their marketing descriptions.
