Odor

An odor, odour or fragrance is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors. The terms fragrance and aroma are used primarily by the food and cosmetic industry to describe a pleasant odor, and are sometimes used to refer to perfumes, and to describe floral scent. In contrast, malodor, stench, reek, and stink are used specifically to describe unpleasant odor. The term smell (in its noun form) is used for both pleasant and unpleasant odors.

In the United Kingdom, odour refers to scents in general. In the United States and for many non-native English speakers around the world, odor generally has a negative connotation, as a synonym for stink; on the other hand, scent or aroma are used by those people to indicate "pleasant smells".

Intensity

Odor intensity is the perceived strength of odor sensation. This intensity property is used to locate the source of odors and perhaps most directly related to odor nuisance.

Perceived strength of the odor sensation is measured in conjunction with odor concentration. This can be modeled by the Weber-Fechner law: I = a × log(c) + b

I is the perceived psychological intensity at the dilution step on the butanol scale, a is the Weber-Fechner coefficient, C is the chemical concentrations, and b is the intercept constant (0.5 by definition)

Odor intensity can be expressed using an odor intensity scale, which is a verbal description of an odor sensation to which a numerical value is assigned.

Odor intensity can be divided into the following categories according to intensity:

0 – no odor

1 – very weak (odor threshold)

2 – weak

3 – distinct

4 – strong

5 – very strong

6 – intolerable

This method is applied by in the laboratory and is done so by a series of suitably trained panelists/observers who have been trained to appropriately define intensity.