Lol well it might also be that humans cant smell air but there are those creatures like dogs which can smell a scent from... however far away~ So its that human noses cant~
Wine tasting people can have very good senses of smell. :)
And yes obviously you don't smell something from miles away, you smell it directly in your nose. There has to be something left behind, or that has spread a great distance. :P
Lol it would suck to be able to sense traces of... natural gasses... in the city~ xD Though that might make you immune to it since you would smell it tons~