Anything that you can smell is a gas. The smell of food is a mixture of gases, just as the scent of a flower and the pong of drains.
Gases mix until they are spread out evenly. So if there is a concentration of a gas in one place (say a flower) the scent (gas) readily mixes with the air. This means that the scent spreads out around the flower. But, as it mixes, it is less concentrated and so it's harder for us to smell it.
