I know that smell! It's the ozone. (O3 ). Going outside before and after the rain you can smell the freshness. I love that smell! Now I know what to call it! Petrichor.
From Jane Fallon's Business of Life post "4 Useful New Words."
You know how it smells after it rains? That clean, greenish smell? That’s petrichor, from the Greek petra (stone) and ichor (the blood of Greek gods and goddesses). The term was coined by two Australian researchers in 1964.