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After I pass the smoke from partially burned fuel oil through a filter, I can still very strongly detect the smell. It is the same thing you smell from the exhaust when an old car or truck goes by.

Even though I can easily smell it with my nose, none of my sensors can detect it. I've tried $\ce{VOC}$, $\ce{O3}$, $\ce{PM_{2.5}}$, $\ce{CO}$, $\ce{NO2}$, & combustible gas detectors and all come up clear on the filtered exhaust.

So what is left in this gas that is responsible for this strong smell (and the resulting headache) and what sensors can I use to detect it?

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In analytical chemistry, sensors refer to analyte specific devices, e.g., glucose sensors, pH sensor etc. Smell on the other, generated by a burning complex mixtures such as fuels can rarely be associated with one compound. People have spent their life (e.g. Alan Marshall) studying the constituents of fuels. There are literally thousands and thousands of compounds.

However, if you were in a research lab investigating odors, you would be using something called as a olfactory gas chromatography technique. There is a chromatography column which separates all the gaseous/volatile components and a scientist puts a nose at the end of the column and records the "response". Later you can identify that particular odor by a mass spectrometer.

In short, there is no sensor per se. You need a instrumentation which would fit in a kitchen sized area to determine what causes that particular odor after burning an extremely complicated mixture such as fuel oil.

Here is how it looks like: Olfactory GC

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  • $\begingroup$ "a scientist puts a nose ..." – Would any nose do? :-) $\endgroup$ – mhchem Jun 12 '19 at 6:19
  • $\begingroup$ Nosy noses are not needed in olfactory GC. Actually, you need a highly trained person's nose. $\endgroup$ – M. Farooq Jun 12 '19 at 13:12
  • $\begingroup$ I was hoping someone had already identified the likely culprit(s) in this very common situation. Any thoughts as to even what kind of molecules could be contributing to this smell? Products of incomplete combustion? Compounds from impurities in the original fuel? Other? Interestingly you do not get this smell from a newer and well tuned engine. Thanks! $\endgroup$ – bigjosh Jun 12 '19 at 16:46
  • $\begingroup$ @bigjosh, have searched Google Scholar for this topic? The moment I search, the second result is a relevant paper. link.springer.com/article/10.1007/s00216-009-3071-7. Read the abstract. You can move on from there by using better keywords. $\endgroup$ – M. Farooq Jun 13 '19 at 0:58

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