What makes rain smell? Bubbles

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By Heather Mendiola

Have you ever wondered why there is a certain smell after the first rainfall in a while, like the smell of a summer rain?

The term “petrichor” was coined in 1960 to describe this distinct smell, when scientists believed that the smell came from the ground that the rain fell on. However, the process for the production of the smell was not known.

Two scientists recently published an article in “Nature Communications” that explained how this process works.

Young Soo Joung and Cullen R. Buie, scientists at MIT, were investigating aerosols and their role as one of the best mechanisms of aerosol dispersion. Joung and Cullen were interested in aerosols’ impact on the environment and on human health.

Joung and Buie were seeing if raindrops were origins of atmospheric bioaerosols with elements of soil or microorganisms.

To test this, Joung and Buie used a high-speed camera to capture the footage of rain droplets hitting different soils at different speeds in order to see if velocity was a factor.

Joung and Buie found that at the velocity of a light rain, rain droplets hitting a sandy clay surface trap air bubbles that contain elements of the soil on which the droplet fell.

When the droplet bursts at this light rain velocity, the bubbles reach the top of the droplet, and, much like carbonation in soda and champagne, the air bubbles burst and the aerosols are released into the air.

If the velocity is higher or lower than that of what is considered a light rain, the droplets will splatter without the bubbles being trapped or released.

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