Why You Can Smell Rain Before an Oncoming Storm
Many of us have experienced being able to smell rain or a storm before it hits. While we might not get quite enough warning to batten down the hatches or even bring the outdoor furniture out of the impending deluge, it can prove enough to know that rain is about to hit and to take shelter under a nearby overhanging roof.
Primarily, we can smell ozone from a variety of sources being charged by the electricity in the atmosphere. As well as being able to smell an impending storm, our noses can pick up on different smells once rain hits and once a storm has passed, all of which are produced by different chemicals and reactions.
The Smell of Ozone
Ozone is also called trioxygen and consists of three molecules of oxygen. When viewed, the gas has a pale blue color, and when smelled it has a strong, pungent aroma. Ozone comes from products like fertilizer, as well as natural sources, including feces. It is also found in some pollutants and other sources.
Ozone is also formed when electricity from lightning splits nitrogen and oxygen molecules into their separate atoms. These can reform to create nitric oxide which then reacts with gases in the atmosphere to create ozone. Thunderstorms also have a natural downdraft, and this pushes the ozone down towards the ground, which is why we can sometimes smell ozone before a big storm hits.
Once the rain is upon us, the aromas we can smell will change. Petrichor, which was named in the 1960s, tends to occur when it rains just after a long dry spell. During this dry period, plants produce the fatty acid petrichor that is used primarily to prevent the plants from growing when there is little or no moisture present to feed on.
When the rain hits the plants and the ground, it breaks up the petrichor, which is released from the soil and gives an earthy smell. If rain is approaching, you may be able to smell the petrichor before the rain arrives, although it is more likely that you will be able to smell this aroma once the heavens have opened.
Another aroma that can be smelt during a light rain is that of geosmin. Geosmin are algae-like spores of bacteria found in soil. When light rain hits the ground, the spores are released via bubbles forming under raindrops. If the rain gets too heavy, the aroma is no longer detectable, so this smell is only present during light rain showers that follow a dry spell.
It is not uncommon to be able to smell an oncoming storm: the pungent aroma of ozone, which is formed with the help of lightning and pushed down from the clouds by the downdrafts of a thunderstorm. Other smells associated with rain usually occur once it is already upon us, including the smell of petrichor, a fatty acid produced by plants after a dry spell, and geosmin, which is a type of algae that is disturbed by raindrops.
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