The Magical Smell of Rain – Petrichor
Here’s a precise, step-by-step explanation of how rain triggers the smell of petrichor:
1. Dry Periods Store Oils and Compounds in the Soil
During dry spells, many plants release oils that accumulate on soil and rocks.
Soil microorganisms called actinobacteria (especially Streptomyces) grow in the soil and produce geosmin, a compound responsible for the earthy scent.
These substances sit quietly in the soil until rain arrives.
2. Raindrops Hit the Ground
When rain begins, each raindrop traps air bubbles as it hits the ground.
These bubbles carry tiny particles from the soil, plant oils, and microorganisms upward.
3. Aerosolization – Smell Gets Released into the Air
As the air bubbles burst at the surface, they release microscopic droplets into the atmosphere.
These droplets carry geosmin and other aromatic molecules with them.
The fine mist spreads quickly through the air, allowing us to smell it.
4. Ozone Adds to the Scent (Sometimes)
During storms, lightning can split oxygen molecules (O₂) and recombine them to form ozone (O₃).
This ozone mixes with rain and air, contributing a sharp, clean scent that enhances the overall fragrance.
5. Humans Detect It Instantly
Our noses are highly sensitive to geosmin—even a few parts per trillion can be detected.
That’s why the smell feels so strong, even though only trace amounts of the molecules are present.
Summary
Rain triggers petrichor by hitting dry soil and releasing stored plant oils and geosmin into the air through bursting bubbles, spreading the scent rapidly. Lightning can also add ozone, making the smell sharper. Our noses are highly tuned to detect these compounds, making the fragrance instantly recognisable and deeply satisfying.