Odor unit, definition

The odorous air sample is diluted automatically with neutral air by use of an olfactometer. This procedure leads to the definition of an odor concentration according to Eq. 7-9 that is applied for the determination of mixing ratios of known flow rates V (dynamic dilution method). The abbreviation ou stands for odor unit (Treitinger and Meyer-Pittroff 1997). The odor concentration is inversely proportional to the dilution. Actually, odor concentrations are dimensionless (see Eq. 7-9) and they simply reflect a dilution to threshold ratio. However, it is common to express odor concentration in odor units per cubic meter ([odor]/ou m ). 

The notion of odour concentration is based on the works of H. Zwaardenmaker, a Dutch scientist and early investigator of the olfactometry. By definition, the odour concentration, expressed in odorous unit per cubic meter (ou/m3) is the dilution factor of the odour sample in clean air in order to just become odour free, i.e. to reach the perception threshold for an "average" person. 

In the following some aspects of the guidelines are given in detail. Guideline VDI 3881 consists of four parts. The drafts of parts 1, 2, and 3 were published in the VDI handbook. Part 4 is in preparation. The draft of part 1 was already revised. The new version will be published in a few months. The most important result of the revision is the definition of odour concentration expressed as odour units per cubic meter (GE/m 3). According to this definition one odour unit is the amount of odorants in one cubic meter of air at odour threshold level. The new definition is a real concentration and gives a better form of input parameter for dispersion models. 

Ethylene (Ethene or Elayl), H2C CH2 mw 28.05 colorless, flammable, dangerous to handle gas with characteristic sweet odor and taste sp gr 0.975 (air = 1.0), mp —169.4°, bp —103.8°, flash p —136°C explosive limits in air, % by vol, lower 3.0 upper 34.0 si sol in w, more in ale sol in eth. Ethylene is a major component of petroleum refinery gas from cracking units, and is sometimes recovered therefrom by distillation or other means. Some pure ethylene is produced by passing hot ethanol vapors over a catalyst, such as activated alumina (Ref 4). Its laboratory prepn consists of heating ethanol in definite proportions with sulfuric acid of certain concns. By using a 90% acid and 90% ale, ethylene can be produced in a regular stream at a yield of 84 to 85% of theory (Ref 2). 

Definition Poiysaccharide extracted from Western iarch wood, Larix occidentalis, having gaiactose and arabinose units in approx, ratio 6 1 Properties Lt. yei. to amber very vise, iiq. baisam pine odor soi. in water m.p. > 200 C (dec.)... 

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