Detection of single and mixed VOCs by smell and by sensory irritation

We have measured complete concentration-detection (i.e., psychometric or detectability) functions to study the olfactory and ocular/nasal chemesthetic (a term that includes sensory irritation) impact of VOCs presented singly and in various binary mixtures. Such functions provide considerably more information than that provided by measuring only a "threshold". The outcome for single VOCs confirmed the much higher absolute sensitivity of olfaction compared to chemesthesis, but also demonstrated that the detection of ocular and nasal sensory irritation increases as a function of vapor concentration at a much higher rate than that for the detection of odor. The outcome for the binary mixtures revealed that, for both olfaction and chemesthesis, complete additivity of detection of individual components held at relatively low levels of detectability but broke down at higher levels. The breakdown for odor detection, compared to that for sensory irritation detection, was, first, more extensive, and, second, dependent to a larger extent on the degree of structural and chemical similarity/dissimilarity between the mixed VOCs.

Concentration-detection functions for the chemesthetic and olfactory detectability of VOCs have shown that, even when nasal pungency and eye irritation begin to be evoked at concentrations orders of magnitude larger than those evoking odor, they sharply increase in detectability to become clearly noticeable. In contrast, odor detectability increases with concentration at a much lower rate. As a result, any fixed reduction (e.g., 10-times) in the concentration of a VOC will reduce detectability of sensory irritation much more dramatically than detectability of odor, within their respective ranges. Concentration-detection functions are particularly informative when employed to probe into the rules of dose- and response-additivity in mixtures. Our results for olfaction, and to a lesser extent for chemesthesis, indicate that additivity of detection of individual VOCs in mixtures is level-dependent: as detectability increases, the degree of additivity decreases. This suggests that a substantial improvement of perceived air quality could follow from control of just the few dominating chemosensory sources.