thumb|Soil and water being splashed by a raindrop

Petrichor ( ) is the earthy scent from an array, in particular, of plant-derived chemicals, produced when rain falls on dry soil. The word was coined in 1964 by Australian scientist Richard Thomas, in a paper co-authored with Isabel Bear which described the phenomenon. which was re-published in its entirety, a month later, in The Scientific American. In the American presentation, he wrote, "This subject, with which I was occupied more than twenty-five years ago, appears... in... the Chemical News to have recently attracted the attention of Professor Berthelot and [Monsieur G.] Andre." Phipson continues, "I find... [from] my old notes... [of] 1865, that it is doubtful whether I ever published... these observations", going on to say, as the problem was not yet solved, he again offered his observations, theorizing that the odour "was due to the presence of organic substances closely related to the essential oils of plants", and that the substances consisted of "the fragrance emitted by thousands of flowers" that had been absorbed into the pores of the soil, only to be released by rain; based on his attempts at isolation, he proposed it as a singular substance, "very similar to, if not identical with, bromo-cedren derived from essence of cedar."<!--No use can be found for this citation: --> Thomas coined the term "petrichor" to refer to what had previously been known as "argillaceous odour".<!--A single primary source does not "show" (prove) anything.-->

Research in 2015 suggested that as the falling droplets of rain impact the surface of various wettable types of soil that are porous, aerosols are generated that "deliver elements of the porous medium to the environment", and suggest that this is the mechanism by which the petrichor scent is generated. Adding to contemporary studies of the decades-old subject of petrichor aerosols, further research suggests that detection of ozone by humans preceding rain—that chemical the product of various soil components and the action of lightning (when relevant)—adds to the phenomena of perichor sensing.

Mechanism

thumb|right|200px|A leaf with droplets on damp soil

Preliminary research in 2015 suggests that when a raindrop lands on a porous surface, air from the pores forms small bubbles, which float to the surface and release aerosols. Such aerosols might carry the petrichor scent, as well as bacteria and viruses from the soil.

In popular reporting, speculation has been offered that camels in the desert may rely on the petrichor scent to locate sources of water such as in oases. Popular reporting has also suggested that some scientists believe humans might appreciate the scent of rain because ancestors relied on rainy weather for survival.

See also

  • Geosmin – a compound contributing to the petrichor scent
  • Dimethyl sulfide – A molecule contributing to the odour of the sea
  • Mitti attar – a perfume recreating the loamy smell of rain

Citations

Further reading

  • "Petrichor" at A Word a Day
  • From the Oxford English Dictionary
  • Petrichor, U.K. Met office.
  • Why Is the Smell After It Rains So Appealing? The Petrichor phenomenon
  • Petrichor – Why we Love the Smell of Rain