What Causes the Smell After Rain?

TL;DR

Thunderstorms and rain release various aromas, including ozone, geosmin, and oils from plants, creating a distinct and pleasant smell.

Transcript

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Key Insights

• 👃 Ozone, geosmin, and plant oils are the primary sources of the smell after rain.
• 💁 Ozone is formed when lightning splits nitrogen and oxygen molecules, while geosmin is excreted by bacteria in the soil during dry periods.
• 😘 The smell after rain is more noticeable in wooded areas due to a lower chance of geosmin infiltrating the city.
• 👃 The chemicals in plant oils that contribute to the rain smell have not been fully identified.
• ❣️ The deep and earthy smell is strongest after a dry spell or heavy rainfall.

Questions & Answers

Q: What causes the clean smell after a thunderstorm?

The clean smell is caused by ozone, a gas formed when lightning rips nitrogen and oxygen molecules apart. It has a pungent and sharp odor similar to chlorine.

Q: Why does the smell after rain become stronger after a dry spell?

The smell after rain becomes stronger after a dry spell because bacteria in the soil, such as streptomyces, produce more spores during overly dry periods. These spores excrete geosmin, which creates the deep and earthy smell.

Q: What are the chemicals released by plants that contribute to the smell of rain?

The specific chemicals in the oils of plants that contribute to the smell of rain are not fully known. However, one possible contributor is two isopropyl three methio-oxipyrosine, which was isolated in the 1970s and has a rain-like smell.

Q: Who coined the term "petrichor"?

The term "petrichor" was coined by Australian chemists Isabel Bear and RG Thomas in 1964. They discovered the oily substance that gives the rain smell by extracting and analyzing oils from dried clay.

Summary & Key Takeaways

• After a thunderstorm, the clean smell is caused by ozone, a pungent and sharp-smelling gas formed from nitrogen and oxygen molecules.

• The deep and earthy smell after rain is a result of geosmin, a chemical excreted by bacteria in the soil during dry periods.

• Oils secreted by plants also contribute to the smell of rain, releasing certain chemicals into the atmosphere.