I am currently working at a nice Holiday Inn that generates a lot of business, and I found out that the familiar hotel-pool-chlorine smell that seems to permeate every hotel is, in fact, purchased. It comes in large buckets, and is a powdery substance. Each morning, someone from maintenance will unlock a small window on the ventilation system, fill a tray with the powder, and slides it in. Voila! The buckets we receive have many codes on them, but I can't track down the company name to find who is responsible, but it sure is interesting regardless.
In addition, we have several scents we'll put into the vents that lead to our ball/catering rooms. We have a leather scent for business, a somewhat fruity scent for parties, and a rose scent for weddings.
Just thought I'd pass this along