Nicotine is the marker chemical for AQ testing of secondhand smoke* (As per air quality researchers nationwide) Nicotine is the only unique or "trace" chemical in secondhand smoke. If you measured for formaldehyde, the carpet and other interior sources of formaldehyde would corrupt the test result, formaldehyde is formed naturally in our atmosphere due to photochemical oxidation. Benzene is given off from burning foods in the kitchen or diesel exhaust outdoors so again a false reading would be obtained. Therefore, nicotine is the ideal chemical to measure to determine secondhand smoke concentrations in the air. And then our comparison to OSHA guidelines is the logical manner in which to determine if secondhand smoke levels pose a health hazard, as you can see, according to OSHA, the authority on workplace safety, they do not.
If you wanted you could measure every airborne chemical in secondhand smoke and then compare them to OSHA guidelines for each specific chemical, the results would be the same, if not more dramatic. To wit, the tobacco companies provide more nicotine content in their products than any other of the alleged chemicals such as benzene, fomaldehyde, arsenic, etc.......isn't that what the tobacco trials confirmed?