I've been away from the blog for a while, so I'll start simple. Why do the worst smells linger the longest? Maybe only my nose/brain works like this, but I can continue to smell something gross (like dog doo-doo) for minutes (sometimes half an hour or so) after I've come in contact with the actual foul-smelling air. I would actually guess that it's my brain that somehow gets hung up and can't stop processing that smell. Not that the smell molecules are somehow still in a cloud around me and that I can actually continue to smell them because they are so terrible that even at very low concentrations my nose can detect them.
Furthermore, it's interesting that really good smells don't seem to ever linger. The most logical explanation is probably that I have a poorer idea of what a really good smell is. For example, I could rate smells on a scale of one to ten and calibrate my bad smell scale by placing the smell of human feces at 9. Now let's say I use that same scale for good smells, I actually can't think of any good smell that's a 9 on the equivalent scale. Bad smells are much worse than good smells are good.