scent

Although the smell of rain is intensely desirable (many people list it among their favorites), attempts to create synthetic petrichor — sometimes called petite pluie in the perfume industry — are fairly rare, and always failures. That is because petrichor, as described by Bear and Thomas, tells a terrestrial ghost story. Like the smell of death and disease in the plaster walls of a nineteenth-century morgue (that’s why they’re tiled or coated with semi-gloss paint today) or the fish stink in an open container of spoiled milk, the ambient odors of any given environment are absorbed from the air by anything porous and stored there. The matrix we call air is filled with an ever-changing bouquet of terpenes and volatile lipid- and carotenoid-derived compounds released during processes of decomposition, metabolism, and growth...The smell of a place at a particular moment could be said to follow the same rules as any perfume, but with a far greater degree of complexity. Typically, a perfume is composed of some head notes (bright smells that dissipate quickly), heart notes (heavier molecules that define the overall smell), and a bottom note (a smell such as sandalwood, which doesn’t dominate a fragrance but may stay on your clothes for days). On a midsummer afternoon after a light rain, the smell of my block in Brooklyn might include petrichor as a heart note. But that would only be the simplest part: there would be head and heart notes of gasoline, rotting food, fallen leaves, pollen, flowers, car exhaust, a great variety of feces from organisms sharing the space, and perhaps bottom notes from the soil, grime, and soot ground into pavement, with an occasional contribution from the East River when the wind is right.

Beau Friedlander, "A Brief History of Scent"