Word of the Month: Petrichor

David Zapatka

Following a good rain after a long, dry spell one evening on the pickleball court with friend Natasha Thompson, that luscious smell we are all familiar with danced in our noses. Imagine that fresh, earthy, smell we all know so well as you read this column. Tash said, “There’s a word for that smell. It’s ‘petrichor.’ I suggest you consider using it for the WOTM column.”

Petrichor: noun pe·tri·chor | ˈpe-trə-ˌkȯr a distinctive, earthy, usually pleasant odor that is associated with rainfall especially when following a warm, dry period that arises from a combination of volatile plant oils and geosmin (a volatile, organic compound formed by soil-dwelling bacteria and aquatic cyanobacteria contributing to petrichor and musty tasting drinking water) released from the soil into the air and by ozone carried by downdrafts.

Origin and Etymology: The word is constructed from Greek petra (πέτρα), “rock,” or petros (πέτρος), “stone,” and īchōr (ἰχώρ), the fluid that flows in the veins of the gods in Greek mythology.

First Used: 1964.

History: The word was introduced by the Australian mineral chemists Isabel Joy Bear and Richard Grenfell Thomas in “Nature of argillaceous odour,” Nature, vol. 201, No. 4923 (March 7, 1964), pp. 993-95. According to the authors, “The diverse nature of the host material has led us to propose the name ‘petrichor’ for this apparently unique odour which can be regarded as an ‘ichor’ or ‘tenuous essence’ derived from rock or stone.”

Mechanism: In 2015, scientists from the Massachusetts Institute of Technology used high-speed cameras to record how the scent moves into the air. The tests involved approximately 600 experiments on 28 different surfaces, including engineered materials and soil samples. 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 carry the scent, as well as bacteria and viruses from the soil. Raindrops that move at a slower rate tend to produce more aerosols; this serves as an explanation for why the petrichor is more common after light rains. Actinomycetes is the bacterium responsible for producing spores in soil.

Used in a song by Paul Kelly:

It hasn’t rained six months or more
Until today, a sudden pour
Now I can smell the petrichor outside
The sighing ground gives up its love
Unto the breeze and the trees above
And suddenly your phantom shoves my side

I don’t need you
I don’t need you
I don’t need you, but I sure want you

I never loved you more than when I turned and walked into the wind
And left you leaning on no friend of mine
I walked straight, didn’t turn my head
The hardest thing I ever did
Seabirds wheeling overhead and crying …

This is a fairly new word at only 56 years old. Do you know others? Please submit your experiences, any thoughts on this month’s column, or any word you may like to share along with your insights and comments to [email protected].