What is Odor?

Odor is one of the chemical substances dissolved in the air usually at a very low concentration, which can be perceived by virtue of the sense of smell. Fragrance and aroma terms are used primarily by the food and cosmetic industry to describe a pleasant odor. Odors are basically classified into two groups, either as unpleasant or pleasant odors based on the perception.

Odor is a sense stimulated by the receptors that perceive the dissolved odor in the air. Although the widest range of odors consist of organic compounds, inorganic compounds such as hydrogen sulfide and ammonia are also odorants.

The effect of odor may be considered in a two-phase process. First, there is a physiological phase; i.e., the detection of stimuli by receptors in the nose. This is followed by the psychological phase. The stimuli are processed by the region of the human brain which is responsible for olfactory modality. Because of this, an objective and analytical measure of odor is impossible.

While the sense of smell completely exhibits very personal perceptions, individual reactions are related to gender, age, state of health, and personal history. Common odors that people are used to, such as their own body odor, are less noticeable to individuals than external or uncommon odors.

For most people, the process of smelling gives little information concerning the specific ingredients of an odor. However, flavorists and perfumers can distinguish small amounts of chemicals in complex mixes through smelling alone.
The concentration of odorants have been defined by a device called the Olfactometer since 1870 in Germany.

Despite not being an objective method, different aspects of odor may be measured through quantitative methods.

For example:
The concentration of odorants, which is the oldest and most important methods to determine odor emission. Determination is carried out with the concentration of odor substrate at the beginning level of odor.
Odor density is based on a scale depending upon the air density. This scale is classified as follows:

Hedonic assessment: The process of scaling odors on a scale ranging from extremely unpleasant to neutral, and up to extremely pleasant. This method is not different from the measurement method of odor density.

Odor types: The said odor is identified by a test subject as stench, pleasant, reeking or malodor. Only a test person is required for the said method.

Sampling method: The test person should take the air sample in an air environment not containing any other air content, because the specific air sample may be affected from other ambient odors. Assessment could be made under suitable environmental conditions and for this reason air samples are kept in a sampling bag. All bags in which samples are kept should be made of odorless materials.

The following acts have been adopted with regard to environmental protection:

Country Refinery Guideline of 1970, Federal Emission Protection Law of 1974, Technical guideline To Keep the Air Clean and Odor Emission Guideline. Despite the fact that smelling machine studies were carried out for determining explosive material, diagnosing cancer and testing perfumes from the beginning of the 1980s to 1998, artificial noses could not be developed in such a way to replace the human nose. The human nose can hardly be imitated in terms of its complex nature and ability to distinguish different odors, even faint ones.

Odor Measurement Methods