Remember that faint, amiable scent that you smell right after rains? Sometimes, you might find the smell quite similar to the freshly cut grass, especially during the spring season. But have you wondered what causes the sweet “after the rain” smell and why it is only after rain, thunderstorm or after watering the soil?
The reason behind the pleasant smell is a type of bacteria species known as Actinomycetes. Actinomycete is a group of filamentous bacteria that grows in soil when the conditions are dry and damp. This particular bacterium plays a major role in the decomposition of organic material. When the soil is completely dry and out of moisture, then it produces spores in the soil. When it rains, the force caused by the rainwater and wet condition draws out the spores into the air, and the moisture acts like deodorant which spread the spores right into the atmosphere. Once the spores are out, they are carried to your nose, giving you the alluring and fresh aroma. The bacterium is found all over the world, giving the most amiable after rain ambiance.
Actinomycete generally goes for moist soil but it produces spores only in dry soil, so the smell is stronger after a dry shower or sometimes dry shower with rainstorm. In addition, the airborne oil combines with the spores to produce the peculiar smell. The bacterium also produces a common substance called geosmin, particularly in forest and moist areas. One other compound known as 2-methylisoborneol is also produced by the bacterium which indicates the soil is fertile or not.
In urban regions, with the growing rate of pollution you might not experience the same pleasant smell as the rain water is acidic with substances like sulfur, heavy metal dust and chemicals which ultimately combine with the surface with gasoline and oil that produces a pungent and unpleasant smell.
