After a string of warm and dry days, the ground starts to dry out. As clouds build in the atmosphere and a healthy downpour moves through, temperatures drop and a recognizable smell starts to fill the air. We typically refer to it as the smell of rain, but it is referred to as petrichor. The word is rooted in Greek mythology. The smell can be the most notable after periods of warm and dry weather.
This smell is the result of chemical compounds breaking down and being released up into the atmosphere as raindrops hit the ground. The bacteria released that we smell is called geosmin. It is an abundant bacteria that occurs naturally in the environment and has that earthy smell and taste. Geosmin is common in foods like root vegetables. The bacteria get caught and while in water droplets, they break apart and bounce off the Earth’s surface into the air helping to release the smell.
The smell can also be created as raindrops fall on grass, plants, and trees. Rain as it falls causes damage to plant hairs which then enables plants to release the chemical compound terpenes. When the leaf surfaces are damaged, it helps to create a stronger smell that is lofted into the atmosphere.
Finally, lightning and the electrical discharge releases the scent of ozone, which is described as a clean smell released into the atmosphere. These ozone particles get caught with falling raindrops and are transported to the surface.
The next time rain or a thunderstorm rolls in, take note of your surrounding. If there is a lot of greenery close by versus bare ground, and what the weather has been like lately will enable you to see if the scent is stronger in certain environments as opposed to others.
Some folks are sensitive to the geosmin scent and do not find petrichor as pleasing of a scent as others. However, the effects of a healthy rain leave the air much cleaner — reducing things such as dust particles and pollen — improving air quality, and for some, leaving behind that wonderful smell of rain!
— Meteorologist Erika Paige