Petrichor: The smell of rain on dry earth.
Petrichor (pronounced PET-rih-core) was coined by two Australian geologists, I.J. Bear and R.G. Thomas, for an article they published in the journal Nature in 1964, "Nature of Agrilaceous Odour." They created the word from two Greek stems: petros (stone) and ichor (in Greek mythology, the substance that flowed through the veins of the gods). The scent, they proposed, comes from an oily essence released from rocks and soil. According to World Wide Words:
The oil is a complicated set of at least fifty different compounds, rather like a perfume. It turned out that the oils are given off by vegetation during dry spells and are adsorbed on to the surface of rocks and soil particles, to be released into the air again by the next rains.
I smelled petrichor Friday night, when it rained for the first time in six months, a teasing prelude to the real wet season that will get under way in November. The smell I detected was more petrol than petros: the aroma of half a year's worth of gasoline and motor oil being released from pavement. The first rain inevitably causes accident rates to rise as California drivers relearn how to negotiate suddenly slick roads.
I've never lived in a place where it rained year round; the very concept is alien. The first time I experienced summer rain I was 30 years old and passing through Pittsburgh, which appeared unseasonably (to my eyes) green for July. Although I was prepared for the weather, to the extent that I'd remembered to pack an umbrella, I couldn't quite believe it. I'm a California native: to me summer means dry, golden hills dampened only by fog; in my world, rain is always accompanied by cold temperatures and dark days. And petrichor is as intoxicating and autumn-evocative as the scent of burning leaves must be to people in other parts of the country.