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The Loss of Odor Through Conjugation, Suppression, and Cross-Adaptation: How One Plus One Can Sometimes Equal Zero



Thomas J. Bruno


Certain sulfur compounds are added to natural gas (and other fuel gases) as a safety precaution, in order to make the fuel detectable without instrumentation at a concentration of 20 percent of the lower explosion limit of methane. A well known but often poorly understood problem associated with the odorization of natural gas is the phenomena of odorant fading, the gradual diminution of the odor. Some of the more obvious causes of fading are fairly well understood, such as adsorption, partitioning (or absorption), chemical reactions (such as oxidation). Among the less well understood mechanisms are those related to the olfaction process itself. Odorant suppression (sometimes called masking), conjugation and cross-adaptation are among a collection of such phenomena that may contribute to or cause fading, but ones which remain enigmatic. They are related to the differential effects that one odorant species will have when mixed with another. Masking is a term that describes situations in which one odorant can overpower the sensation of another. Conjugation describes the situation in which two odoriferous compounds, when sniffed together, produce the sensation of no odor, or very little odor. Cross adaptation is the desentization effect produced by one odoriferous compound on another. In this review, the basics of olfaction will be discussed briefly, followed by a description of masking, conjugation and cross adaptation. How these phenomena might relate to natural gas fading will then be discussed.
Proceedings Title
GTI Conf. on Natural Gas and LP Odorization
Conference Dates
August 2-4, 2004
Conference Location
Chicago, IL


cross-adaptation, masking, odorant conjugation, Zwaardermaker pair


Bruno, T. (2004), The Loss of Odor Through Conjugation, Suppression, and Cross-Adaptation: How One Plus One Can Sometimes Equal Zero, GTI Conf. on Natural Gas and LP Odorization, Chicago, IL (Accessed July 25, 2024)


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Created August 2, 2004, Updated January 27, 2020