Both olfactometry and physical-chemical analysis are two methods used to evaluate the somehow relative annoyance caused by odorous substances. These techniques have several advantages and also some drawbacks although they can provide complementary information.
With the olfactometry technique odour threshold can be quantified but in most cases these parameters cannot be chemically linked to a substance or group of substances. On the other hand, a physical-chemical analysis can identify single substances that could be related with odorous episodes, but in most of the cases these relation is not possible. Physical-chemical analysis proportionates also information about the toxicity of certain odorous gases, however, there will hardly be a link between concentration of a substance and odour annoyance using this technique. As a short example, more than 500 molecules have been identified in a sample taken from a landfill (terpenes, sulphides, aldehydes, acids, acetones, alcohols, aromatic compounds, chlorides, esters, etc.).