Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Odor threshold value (OTV) (also aroma threshold value (ATV)) is a measure of the odor intensity of a substance. It is defined as the most minimal concentration of a substance that can be detected by a human nose. Some substances can be detected when their concentration is only few milligrams per 1000 tonnes which is less than a drop in olympic swimming pool. Odor threshold value can be expressed as a concentration in water or concentration in air. Examples of substances with strong odors: (Z)-8-tetradecenal (OTV = 0.009 ppb in water), p-vinylguaiacol (OTV = 10 ppb)