Why does a scent fade away in time?

Yesterday when I entered the (empty) elevator I smelled a strong scent of chinese food.
It was pretty strong, i suspect the one carrying it had just left the lift before I came in.
I didn’t like it very much I don’t know why exactly, because I do like it when it is on my plate, but half way to my floor the scent had ‘faded’to a mere whiff, pretty bearable.
I find the same thing when I enter a toilet where the person before me just did a number two.
Which made me wonder:
Why does a scent seem to get less strong in (a relatively short) time, while with other senses that doesn’t seem to be the case the statue that you see doesn’t fade, the cd that you hear doesn’t fade, the fabric of your favorite sweater doesn’t fade when you touch it?