Have you ever wonder why is there a smell whenever a rainstorm is coming? Did you ask yourself why is there this stench after it had rained?
To start off, ozone is the smell you get right before a storm hits. It’s caused by ozone being blown down from the stratosphere by a low-pressure system. In comparison, petrichor is the odor you get after or during a rainstorm. It’s caused by moisture coming into contact with geosmin in the soil.
Petrichor is the culprit
Bacteria living in the soil and on surfaces such as pavement and vegetation react with the water to produce that distinct odor. The scent is more pronounced when there is a longer duration between rain events. It is scientifically referred to as ‘petrichor’. You may smell it before a rainstorm because winds transport the smell over large distances.
More specifically when raindrops impact dry, porous surfaces, tiny bubbles are produced. This launch droplet containing bacteria and organic matter into the air. The droplets and the aerosols that are formed are what’s lofted by the wind and carry the smell with it.
The smell is called petrichor, and it’s the result of a reaction between a compound called geosmin in soils and other natural surfaces when they come into contact with water after being dry for a prolonged period of time.
Fun fact: the human nose is extremely sensitive to geosmin and can detect a concentration as low as five parts per trillion. It’s been suggested that humanity evolved to detect that scent because it tended to guide us towards fresh pastures and food.