Book 24, Question 24
Why does the ground smell so fresh after rain?
The smell has a name: petrichor. When raindrops hit dry soil, they trap tiny air bubbles that burst and send out a mist of smelly particles. Some of the smell comes from oils made by plants, and some comes from a chemical called geosmin that soil bacteria make. People can smell geosmin in very tiny amounts, perhaps because it signals water nearby.
More fun facts
- Scientists at MIT used high speed cameras to watch raindrops hitting soil and other surfaces.
- They ran about 600 experiments on 28 different surfaces, including 16 kinds of soil.
- Some of the soil came from around the MIT campus and along the Charles River in Boston.
- Like the bubbles in a fizzy drink, the air trapped by a raindrop shoots upward and bursts into a mist of tiny particles called aerosols.
- Light and moderate rain made many more of these tiny particles than heavy rain did.
- The tiny drops can also carry soil bacteria, and gusts of wind can spread them around.
Sources: MIT
Questions kids ask
Why is the smell strongest after a light rain?
Light and moderate rain make many more tiny scent-carrying droplets than a heavy downpour does.