Step outside after the first rain and experience the sweet, fresh, powerfully evocative smell of fresh rain.
You are not alone, if you've ever noticed this mysterious scent and wondered what's responsible for it. You know the smell of rain very well. Some people claim they can smell precipitation before it comes. Some may find this pleasant, others may not.
There are bacteria in the ground cause this "rain smell".
"Actinobacteria" includes some of the most common soil life, freshwater life and marine life. It plays an important role in the decomposition of organic material. Thus, it also plays an important role in the turnover of organic matter and the carbon cycle. Some types of Actinobacteria, the Actinomycetes, are responsible for the odor that comes from the soil after it rains in warmer climates.
The specific chemical that causes this odor is called Geosmin.
Some plants secrete oils during dry periods, and when it rains, these oils are released into the air. The second reaction that creates petrichor occurs when chemicals produced by soil-dwelling bacteria known as actinomycetes are released. These aromatic compounds combine to create the pleasant petrichor scent when rain hits the ground.
Another scent associated with rain is ozone. During a thunderstorm, lightning can split oxygen and nitrogen molecules in the atmosphere, and they in turn can recombine into nitric oxide. This substance interacts with other chemicals in the atmosphere to form ozone and this has a sharp smell faintly reminiscent of chlorine.
Another reason for the smell caused is the acidity of rain. Because of chemicals in the atmosphere, rainwater tends to be a little acidic, especially in urban environments. When it comes in contact with organic debris or chemicals on the ground, it can cause some particularly aromatic reactions. It breaks apart soil and releases minerals trapped inside, and it reacts with chemicals, such as gasoline, giving them a stronger smell.
And you thought you were imagining that hard to miss smell of rain.