After a rainstorm, especially a rain storm that breaks a long dry spell, the world smells different. What causes that strange, clean, earthy smell? A few things that aren't so clean.
Right after the rain there's an intense smell that you have to huff while you can. It's incredibly strong. People everywhere notice it, and scientists have a few theories as to what causes it.
Some of the smells, especially the parts that people identify as "clean," probably come from ozone. Ozone is sometimes used to kill off odors, especially smoky and moldy odors.
The clean scent after a rainfall is partially caused by ozone cleaning away some of the scents we take for granted. The other main scent of a rainstorm is a sort of rich earthy smell, like freshly turned-over dirt. Actually, it's exactly like freshly turned-over dirt.
When the soil dries out, there are bacteria that put out spores that can survive in the dry dirt. And then when it rains, the rain dampens the soil and kicks up the spores, so the scent is the of the bacteria in the air and dirt, going to work again.