What Is the Smell of Rain Called? Petrichor and the Science Behind It

The earthy smell that often rises when rain hits dry ground is called petrichor. Australian researchers Isabel Joy Bear and Richard Thomas coined the term in a 1964 Nature paper (Bear & Thomas, 1964).

Petrichor is a mix of smells, not a single substance. Plant-derived oils and compounds from soil microbes contribute to the earthy scent. Ozone can add a sharp, clean note before a storm, though it is separate from the smell released by wet ground.

What causes petrichor?

Bear and Thomas described oils that collect on soil and rock during dry weather. When raindrops strike these surfaces, they can send tiny droplets into the air, carrying some of the compounds with them. This helps explain why the first rain after a dry spell may smell stronger than rain falling on already-wet ground.

Another contributor is geosmin, an earthy-smelling compound produced by soil bacteria and other microorganisms. The EPA lists geosmin among compounds associated with earthy and musty odors. It can be detected at low concentrations, which helps explain why a small amount can make a noticeable impression.

A third possible component is ozone. It has a sharp smell and may be noticed ahead of a storm when air movement carries it toward the ground. The American Chemical Society discusses ozone as one part of the smell sometimes associated with approaching rain. It is distinct from the earthy scent that comes from wet soil.

The balance between these smells varies with the weather and the surface. Some showers bring a clear earthy scent; others have little noticeable smell. The word petrichor is most often used for the earthy smell associated with rain on dry ground.

Why the smell changes with the weather

Dry conditions give plant-derived compounds time to collect on surfaces. The first drops can release some of them into the air. Once rain has wetted the ground, there may be less of this accumulated material available, so later rain can smell less earthy.

The strength of the smell also depends on what the rain hits. Soil and garden beds contain organic material and microorganisms that can contribute to an earthy odor. A paved surface has less of that material, so rain on pavement may smell different or less strongly earthy.

Ozone, when present, can be noticed before the rain reaches you. The timing helps distinguish it from petrichor: a sharp, clean smell in the air may precede the storm, while the earthy note tends to arrive as rain hits the ground.

One example: the first rain after dry weather

Imagine a garden that has been dry for several days. As the first drops fall, you notice a damp, earthy smell. That is the kind of scent people usually mean by petrichor. Compounds from the dry surface and geosmin from soil microbes may contribute.

If the air smelled sharp before the drops arrived, ozone may also have been present. As the rain continues, the earthy smell may weaken as the surface gets wet. The exact scent and timing depend on the weather and the ground, so this is a useful way to think about the components, not a test that identifies them with certainty.

Key Takeaways

• Petrichor is the name for the earthy smell often associated with rain falling on dry ground.
• The term was coined by Isabel Joy Bear and Richard Thomas in a 1964 Nature paper (Bear & Thomas, 1964).
• Plant-derived compounds and geosmin from soil microbes can contribute to the smell.
• Ozone may add a sharp, clean odor before a storm, but it is separate from the earthy scent released when rain hits the ground.
• The smell can vary with recent weather and the surface receiving the rain.