Fresh Ideas and the People Who Bring Them to Life
Fresh Idea #4: Film The Smell of Rain
Back in the 50s, a friend’s uncle invented the wetsuit. Hugh Bradner got a job with U.C. Berkeley that required him to dive in the chilly Pacific. One idea led to another, and Dr. Bradner discovered that when trapped in a foam-like fabric (neoprene) water in the form of bubbles could warm to the body’s temperature, acting as insulation. Recently, a couple of scientists at the Massachusetts Institute of Technology made another bubbly discovery.
You know that wonderful smell that fills the air after a welcome rain. It has a name: petrichor, a word coined in the 60s by scientists who learned that the smell came from the surface the rain landed on. Still, nobody could understand the process until this year when the two MIT researchers had the idea to use high-speed video to catch the rain working its magic.
Documenting different size raindrops falling at different speeds onto dozens of surfaces—from aluminum to sand—they learned that when rain falls at just the right velocity onto the right kind of soil, the drops turn into champagne. Well, not literally, but when a raindrop lands on dirt with certain bacteria, viruses and other particles, it traps the miniscule air bubbles that hold these particles. As the water drops fall apart, the aerosols quickly shoot up, like the bubbles in champagne, jetting out into the air.
The perfect recipe for the heavenly scent is a light, steady rain on thirsty soil. The scent isn’t in the rain; the rain releases petrichor from the plains of Spain or, hopefully, the dry fields of California.
That the word petrichor comes from the Greek petra, meaning ‘stone’ and ‘ichor,’ the fluid that flows in the veins of the gods, is interesting because it hints at the fact that raindrops disperse viruses and bacteria into the air as well as scent, the implications of which make the study more important.
Note: Cullen R. Buie, an assistant professor of mechanical engineering and postdoctoral researcher, Youngsoo Joung, published their article, “Aerosol Generation by Raindrop Impact on Soil,” in Nature Communications.