气味是一种 “精神物理” 现象。这种“精神物理”涉及人体器官对由“五官”所接收的环境变化的反应。比如，人体对声音，对光亮，或气味的感觉。在“五官”中，“嗅觉”在结构和组织上是最复杂的。人类的嗅觉支持80%的当吃东西时品出的味道感觉，嗅觉系统通过对恶嗅和刺激创造恶心的感觉来达到并实现对人本自身的保护机制。这种机制主要是通过两种神经组织来完成的: 一个是嗅觉神经(第一脑神经) 负责处理对化学"气味物质"的感应；另一个是三叉神经(第五脑神经) 处理对化学 “刺激物质”的感应。 气味可用下面的术语和方法来表示: Odor is a Psychophysical Phenomenon. Psychophysics involves the response of an organism to changes in the environment perceived by the five senses. Some examples include how the human body perceives sound loudness, lighting brightness, or odor strength. Of the five senses, the sense of smell is the most complex and unique in structure and organization. While human olfaction supplies 80% of flavor sensations during eating, the olfactory system plays a major role as a defense mechanism by creating an aversion response to malodors and irritants. This is accomplished with two main nerves. The olfactory nerve (first cranial nerve) processes the perception of chemical odorants. The trigeminal nerve (fifth cranial nerve) processes the irritation or pungency of a chemical odorant.
由于用标准的空气监测议器难以对付气味成份的多样性和定量气味监测，气味测试可采用与ASTM方法 E 679一致的方法。最常见的气味监测方法是 “气味阀值” 法，它可代表气味的浓度或强度。气味是可以量化的，这种量化是通过把气味样品稀释到刚好可以使受过训练的人的嗅觉神经感应得到的最低浓度时的稀释倍数。气味阀值越高，表示此气味强度需要更多的稀释倍数来达到人体最低感应浓度，同时也表示此气味强度越强。 Odor testing can also be performed in accordance with ASTM Method E 679 (modified) due to the subjectivity of odor detection and the difficulty in quantifying odors using standard air monitoring equipment. The most common measure of odors is the OTV, also referred to as the odor concentration or odor strength. Odor strength is quantified by determining the amount of dilution needed to bring the odorous air sample to its threshold. The higher the threshold value, the more dilution is needed to bring the odor to threshold, thus the stronger the odor.
这样的方法是利用一种空气稀释议器，动态地把气味不断稀释，并让一个训练有素的工作小组来闻，刚好闻出气味时的稀释倍数做为此气味的 “气味阀值”。 所以，气味阀值是一个 无纲量的 “稀释率”， 常用 “气味单位”(O.U.) 表示。有时，为了计算气味的产生溢出率，也用“气味单位/每立方”(O.U./m3) 来表示。The odor threshold is determined by trained human assessors observing presentations of the odorous air sample dynamically diluted with an Olfactometer. The odor threshold is reported as a dimensionless dilution ratio; however, often the pseudo-dimensions of “Odor Units”(O.U.) are used. Units of “Odor Units per cubic meter” (O.U./m3) are also commonly applied in order to calculate odor emission rates.