California has had its share of woes surrounding the topic of rain. Too much results in catastrophic mud slides and too little creates a parched landscape crying out for moisture.
Still, for me, one of the best smells on earth will always be the scent of fresh rain falling on mountain soil after a long dry spell. It made me smile the other day to learn that this scent actually has a name — and not only a common name, but an official dictionary definition — pet·ri·chor (ʹpe ͵trī kôr/)
The definition of petrichor is “The scent of rain.” A pleasant smell that frequently accompanies the first rain after a long period of warm, dry weather.” Or one could say, “the invigorating scent of petrichor rising off the forest floor gave me new energy to make it to the peak.”
The word “petrichor” was coined in 1964 by two Australian researchers, Bear and Thomas, for an article in the scientific journal Nature. It is constructed from the Greek, petra, meaning ‘stone,’ combined with ichor, the fluid flowing through the veins of the gods in Greek myths. Petrichor literally means the blood of the gods hitting stone. Pretty awesome word (in my humble opinion).
For those interested in the science of it, petrichor’s uniquely refreshing scent is actually a mix of two (sometimes three) distinct aromas and comes about through the combined work of plants and bacteria.
During dry periods a variety of plants produce an oil that is absorbed into and stored up in clay-based soils and rocks. When rain finally comes, this oil is released into the air along with geosmin (a metabolic by-product of certain Actinobacteria), which is emitted by wet soil, producing the invigorating scent to the delight of many a forest wanderer. Add in the fresh, biting smell of ozone that comes from lightning and you have one heady perfume.
For the true nature geek, consider this experiment. In 2015, Massachusetts Institute of Technology scientists used high-speed cameras to record how petrichor’s scent moves from the pores of the earth into the open air.
When a raindrop lands on a porous surface (like soil or some types of rock), air from the pores forms small bubbles that float up to the surface and release aerosols (a fine mist of particles). These aerosols carry the aroma and set it free in the outside world for your delighted nose to inhale.
Slower, lighter rainfalls tend to create far more dispersal of these aerosols — so chances are you will get your best nose full during or following a light rain, rather than a deluge of epic proportions.
So next time it rains (whenever that may be), head outside and take a deep breath of one of Mother Nature’s most heady perfumes—the long awaited scent of rain.