Olfactometry

Olfactometry is the scientific method used to quantify odor by human sensory perception. In practice, it involves dynamic olfactometry, where an air sample containing odor is diluted with odor-free air and presented to a panel of trained assessors in a controlled laboratory environment to determine odor concentration.

The key metric is odor concentration, often expressed as odour units per cubic meter (ou/m3), derived from the dilution-to-threshold factor at which the panel detects the odor. A reference odorant, commonly n-butanol, calibrates panel sensitivity and standardizes results. The higher the dilution required to reach detection, the stronger the odor source is considered.

Equipment consists of a dynamic olfactometer, which provides a series of controlled dilution steps, and a sensing chamber where assessors sample air. A typical panel comprises several trained judges (often 5–8). Assessors perform a detection task using a standardized method, such as forced-choice, to minimize bias. Results are averaged and adjusted for variability, with quality control procedures to ensure repeatability and inter-laboratory comparability.

Standards and guidelines for olfactometry are promulgated in Europe by EN 13725 (determination of odour concentration by dynamic olfactometry). Additional international guidance covers sampling, calibration, panel selection, and reporting of results. Limitations include the subjective nature of odor sensation, panel variability, and the influence of environmental conditions during sampling.

Applications include environmental impact assessments, regulatory compliance for industrial emissions, odor nuisance management around wastewater treatment plants and landfills, and research into odor control technologies. Olfactometry does not identify chemical compounds, but provides a standardized measure of perceived odor strength relevant to human experience and regulation.