How does water vapor condenses in the atmosphere?

The air itself cools to below the dewpoint. But there actually are surfaces in the sky, very small ones such as dust and salt particles. They are critical to droplet formation. Without them, the moist air would have a very hard time condensing the water out. It would have to be cooled to well below the dewpoint before enough water molecules could get together to form a droplet. But once it did that would be a sight because that highly subcooled droplet would suddenly be the surface that all the water would condense on, and it would get real big, real fast.