Can you help me understand aerosols (see details)?

Specifically, I can’t understand why reducing a chunk of solid matter or a droplet to a very small size makes it capable of being suspended in the air.

I mean, a fine mist of water is still composed of little bitty spheres of liquid water, so they have the same density as any larger volume of water. If you were to enlarge one of those droplets to the size of a grape, it would drop like a rock through the air, so why does scale matter?

Same with the cloud of soot belching from a diesel exhaust; that’s little chunks of carbon. Lumps of coal can’t hang in the air, so why can these?