I do indoor air quality work with schools. Lots of schools are old, and suffer from indoor air quality problems. Odors are a common complaint, but they're a great diagnostic for bad ventilation. Here's a typical situation -- there's a classroom, and across the hall, a bathroom. The bathroom is supposed to have an exhaust fan running all the time, because a bathroom is a potent source of indoor contaminants (and not just from the obvious, but also for the powerful cleaning products used there). If this exhaust fan isn't working, because maybe the rubber belt connecting the motor to the fan has deteriorated over time, then the air from the bathroom can get sucked into the classroom across the hall.
This is a problem, obviously. But sometimes it's hard to convince those in charge that it needs fixing. Sometimes nobody knows how to fix it. (Because sometimes, just because you have a job doesn't mean you're good at it.)
When things get real crazy, the workers can convince their employer to get an "air test" in their classroom. This is usually not a good idea, because they will usually not find anything, whether it's there or not, and your problems will thenceforth be dismissed, regardless of their validity. There's other ways of diagnosing indoor air quality problems.
But sometimes it does work. I'm talking about a gas canister sample, sometimes called a TO-15. An environmental specialist will bring a metal canister into your room, twist off the top, and let it suck in the air in your room for a couple minutes. Then they close the canister, bring it back to a lab, release all the air that was sucked in from your room, and analyze it. Then they spit back a long list of the VOC's found, usually scary-sounding chemicals that are actually just your deodorant, hair gel, perfume, etc. But every once in a while, I get a hit on 1,4-Dichlorobenzene, and that's when I can say aha. The air from the bathroom is getting into your classroom.
The VOC 1,4-Dichlorobenzene is the smell of a urinal cake, also described as "mothball-like." I don't know why it was chosen as THE smell of urinal cakes, but it is, and it doesn't belong in your classroom.
Had we just fixed the exhaust fan in the first place, we could have skipped all the steps in between. But sometimes things have to be difficult.