dilution

Detection threshold (DT)

Detection threshold is essentially the minimum amount of odorant that can be perceived (smelled).  This minimum amount represents the odour concentration and is a measurement of 1 OU (1 odour…

Read more

Dilution factor

A ratio of diluting neutral gas to odourous sample gas.  According to ASTM E679, this is a ratio of diluting gas to the odour sample.  According to the EN13725, this…

Read more

Dynamic dilution

Mixing of odourous gas and odour-neutral air measured by flow rate. The consistent introduction of odour-free or odour-neutral air to a concentrated amount of an odourous gas allows for an…

Read more

EN 13725 – YES/NO Mode

The assessor is asked to evaluate gas presented from a specific port and to indicate if an odour is perceived ( YES/NO). The assessor is aware that in some cases…

Read more

EN 13725 – Forced Choice Mode

The assessor is presented with two or more ports, of which one presents the stimulus and the other(s) neutral gas.The location of the stimulus in consecutive presentation is randomly distributed…

Read more

Exposure

Exposure is a combination of the amount of a pollutant in the air and the amount of time that person stays in the presence of a pollutant. Exposure determines the…

Read more

Federal Clean Air Act (FCAA)

A federal law passed in 1970 and amended in 1974, 1977 and 1990 which forms the basis for the national air pollution control effort. Basic elements of the act include…

Read more

Hazardous Air Pollutants (HAPs)

Pollutants released into the atmosphere as particles and volatile organic compounds (VOCs) — including the known carcinogens of benzene and toluene — from a variety of sources such as vehicle…

Read more

New Source Review (NSR)

A Clean Air Act requirement that State Implementation Plans must include a permit review,  which applies to the construction and operation of new and modified stationary sources in Non-attainment areas, to…

Read more

Odour intensity

A measure of how strong an odour may be based on an initial perception.  Odour intensity and odour concentration have a non-linear relationship.  For instance, if two distinct odours are…

Read more