Evaporation after rain. Why do many people love the smell of gasoline, damp earth and old books. Le Sillage Blanc by Parfums Dusita

Many people like the smell after rain. It gives not only a feeling of freshness, but also - how to say - calmness in the world. Did you know that this smell can kill you? That's right, as a result of rain, (in most cases harmless) bacteria rise into the air, which in very rare cases can be pathogens of serious diseases. Scientists for a long time could not understand exactly how this process works, but finally figured it out.

A group of researchers published in scientific journal Nature article explaining how this “earthy smell of freshness” gets into our noses after rain. First, it should be said that the fragrance that we feel after the rain does not produce Fresh air and grass, golden in the glimpses of the rays between the clouds. This smell exudes an organic substance called geosmin. It is produced by various classes of microorganisms, including cyanobacteria, actinomycetes. This was known before today, however, scientists could not understand how this substance is sprayed into the air due to the fall of ordinary raindrops.

“Using high-speed cameras and fluorescent dye, the scientists were able to record water droplets falling on different types of soil that contained this organic matter. The recorded footage clearly shows how the droplets literally catapult microbes into the air.

When a drop falls to the surface at a certain speed, it captures the air bubbles formed under it, each of which has a diameter no larger than a human hair. The air bubbles then pass through the droplet and eventually burst. As part of this process, tiny trickles of water rise into the air, and some of them may contain disease-causing bacteria, which are then spread through the air.”

Scientists have found that when just one drop falls, hundreds of tiny bubbles are released, each of which can contain thousands of live bacteria. Inside these almost invisible bubbles, bacteria can only survive for about one hour. But as soon as they are released into the air, they are picked up and carried by the wind. As Cullen Bui notes, one of the researchers of this scientific project, the next challenge for scientists will be to figure out how far these bacteria are able to spread in this way.

The organic matter itself is not particularly remarkable and, as it turned out, does not pose any danger to the body. However, the reason Bui and her colleagues chose to undertake this study is because previous studies have shown some level of association between the prevalence of melioidosis and rainy seasons in South-East Asia and northern Australia. The disease itself is treatable, but without the availability of suitable antibiotics, mortality among affected people can be as high as 90 percent.

This is far from the first study in which scientists have tried to link the extent of melioidosis to rainfall levels, however new job complements our understanding of this problem. At the end of their article, the scientists report that we should not worry about this extremely rare disease. And almost all of us can breathe freely, without fear, and enjoy the pleasant smell after the rain.

What is this smell that is in the air before the rain (some people like it, others don't)? I lived in different parts country, but did not feel the difference ... As soon as this smell appears, you immediately know that it will soon begin to rain.

This smell is called petrichor - the smell of rain falling on dry ground. It appears due to several compounds in the soil, one of which is called geosmin, i.e. the scent of the earth.

The human sense of smell is generally considered not a very strong instrument, being extremely sensitive to geosmin. We can only feel it at the level of only ten trillion. Unfortunately, in modern world it is considered more of an irritant, as in our haughty times, many prefer the scent of engine oil and ozone to the sweet scent of the planet. But I would venture to suggest that things were very different in the distant past.

Geosmin is derived from several types of bacteria and algae that produce a volatile compound that is released as a result of soil disturbance, such as gardening or heavy rain. As soon as rain approaches, a few geosmin molecules waft up to us, which means the rain gets into the wind, and after a while it will fall on us.
Despite the fact that we are used to it, geosmin goes a long way, and can often be very unpleasant for us. Geosmin and another odorous compound, 2-methylisoborneol, can make wine taste earthy, make water nasty, and fish smell bad. (Catfish are especially susceptible to it). The smell of geosmin can indicate to farmers the health of the soil. At the same time, people who are far from Agriculture, prefer to remain ignorant in this matter.

This substance is present in some repellents, although geosmin appears to be harmless to most animals, and is not itself toxic. In fact, its mechanism of action is still unknown, and no one knows why we are so sensitive to it, and because most scientists are quite practical by nature, they prefer not to study it. But the lack of facts has never stopped me, and in this case we have some information to think about.

Several British scientists were interested in the question of how bactrian camels can feel water at a distance of 50 kilometers in the Gobi desert. They suggested that in fact, the animals smell geosmin, which is brought by the wind from the oases.

This survival feature, so useful for camels, could also serve humans. Many years ago we were mostly nomads wandering in the dry regions. It is easy enough to imagine exhausted groups of people wandering the desert without maps in search of the nearest source of water. Suddenly the wind picked up, and what did they find? If they do not have the appropriate olfactory fitness, then nothing, with all possible catastrophic consequences. Well, if they were lucky, they could smell the faint smell of damp soil, which meant they would survive another day.

During the rain and after it, we really smell, at times very saturated - especially after a long drought. The smell of rain even has a term - petrichor (petrichor). It was introduced by researchers Isabelle Beer and Roderick Thomas in 1964 in an article published in Nature. The term "petrikor" is composed of two Greek words- "petra", stone and "ichor" - a liquid that flows in the veins of the gods. And this etymology is not accidental, since the smell of rain is the aroma emanating from the soil.

The main contribution to the formation of the smell of rain is made by soil microorganisms, mainly actinomycetes and cyanobacteria. When they die, including from a lack of moisture, the substance geosmin (geosmin), trans-1,10-dimethyl-trans-9-decalol, is released.

By the way, the name "geosmin" comes from geo - earth and smell - smell. The mechanism of biosynthesis of this substance by bacteria was discovered quite recently - in 2006. We now know that bacteria have a special enzyme, geosmin synthase, that converts farnesyl diphosphate in two steps and produces this terpenoid.

Geosmin builds up in the soil until it rains. Water extracts this substance and gives it to the atmosphere. This smell cannot be called pleasant, although many poets and writers like it. And our noses can smell tiny amounts of geosmin—at a concentration of five parts per trillion, or one teaspoon in two hundred Olympic pools. The unpleasant smell that periodically appears near the lake water is also associated with geosmin.

But the smell of rain is wonderful, because in addition to geosmin, it contains a variety of aromatic oils. In dry weather, when moisture is scarce, plants produce them to slow down their growth and greatly reduce their water intake. These oils accumulate in the soil and are released into the atmosphere as aerosols when it starts to rain.

Finally, there is a third component of the smell of rain - ozone. It is formed due to electrical discharges in the atmosphere before and during a thunderstorm and accumulates in the higher layers of the atmosphere. But during a storm, downdrafts of air throw ozone into the lower layers of the atmosphere, adding bright colors to the palette of rainy aroma.

In 2015, researchers at the Massachusetts Institute of Technology using a high-speed camera, they observed how the aroma from the soil passes into the air. They performed 600 experiments on 28 different surfaces. In slow motion, you can clearly see how bubbles begin to form in a drop of rain that has fallen on the soil, which break out, as if in a glass of champagne. This is how aerosols are released into the air, containing not only aromatic substances, but also the bacteria themselves. The authors of the study write that a single raindrop "can generate hundreds of aerosol droplets within a few microseconds." Wind gusts carry aerosols both horizontally and vertically. That is why soil bacteria are found even high above the ground.

And today we are already addressing the issue of the smell of rain.

You may not have heard, but in 1964 two Australian scientists coined the term Petrichor, derived from the Greek petra ("stone") + ichor ("ichor", a liquid that flows in the veins of the gods into Greek mythology) to refer to the fragrance that remains in the air after the rain has passed.

In the formation of this smell takes part organic compound called geosmin. Translated from Greek, this word means "smell of the earth." Geosmin is a product of the vital activity of soil bacteria of the genus streptomycin and blue-green algae. The most pronounced smell of geosmin can be found, for example, in an earthen basement. Also, this smell is associated with "dampness", "humidity", "mustiness".

And what is the danger here?

During dry periods, some plants release oils, and when it rains, oil vapors are released, creating fragrance. The second reaction that creates this odor occurs when chemicals produced by soil bacteria known as actinomycetes are released. When the soil dries out, the bacteria release spores into the soil. The force of rain droplets lifts these tiny spores into the air, where the moisture from the rain acts as an aerosol. Wet air easily conveys spores to us, and we inhale them. These spores have a specific smell of the earth, which we often associate with rain. Because these bacteria thrive in moist soil, and release spores when the soil dries out, the odor is most noticeable after rain following a drought, although it can be noticed to varying degrees after most rainstorms.

Another type of smell is due to the acidity of the rain. Due to the presence of chemicals in the atmosphere, rainwater tends to be somewhat acidic, especially in urban environments. When it comes into contact with organic debris or chemicals in the soil, certain specific aromatic reactions occur. Rainwater breaks down the integrity of the soil, washing out the minerals it contains, and reacts with chemicals such as gasoline, giving them a stronger odor. These reactions usually produce less pleasant odors than bacterial spores, so the smell is not always good after rain. Like the aroma of bacterial spores, the smell chemical reactions most noticeable when it rains immediately after a dry period. This is because, once dissolved by one shower, they do not enter into the same reaction with rainwater.

Another smell, felt after the rain, comes from essential oils that distinguish plants and trees. Oil accumulates on surfaces such as rocks. The rain reacts with the oil on the rocks and carries it in a gaseous state through the air. This smell, like the smell of bacteria spores, the smell of freshness, is liked by many people. It is even bottled and sold for flavoring!

After rain, (mostly harmless) bacteria rise into the air, which in very rare cases can be pathogens of serious diseases. Scientists for a long time could not understand exactly how this process works, but finally figured it out.

A group of researchers published an article in the scientific journal Nature explaining how petrichor gets into our noses. Scientists could not understand how this substance is sprayed into the air due to the fall of ordinary raindrops.

“Using high-speed cameras and fluorescent dye, the scientists were able to record water droplets falling on different types of soil that contained this organic matter. The recorded footage clearly shows how the droplets literally catapult microbes into the air.

When a drop falls to the surface at a certain speed, it captures the air bubbles formed under it, each of which has a diameter no larger than a human hair. The air bubbles then pass through the droplet and eventually burst. As part of this process, tiny trickles of water rise into the air, and some of them may contain disease-causing bacteria, which are then spread through the air," the article says.

Scientists have found that when just one drop falls, hundreds of tiny bubbles are released, each of which can contain thousands of live bacteria. Inside these almost invisible bubbles, bacteria can only survive for about one hour. But as soon as they are released into the air, they are picked up and carried by the wind. As Cullen Bui, one of the researchers of this scientific project, notes, the next task for scientists will be to find out how far these bacteria are able to spread in this way.

The organic matter itself is not particularly remarkable and, as it turned out, does not pose any danger to the body. However, the reason Bui and her colleagues chose to undertake this study is because previous studies have shown some level of association between the prevalence of melioidosis and rainy seasons in Southeast Asia and northern Australia. The disease itself is treatable, but without the availability of suitable antibiotics, mortality among affected people can be as high as 90%.

This is far from the first study in which scientists have attempted to link the extent of melioidosis to rainfall levels, but new work adds to our understanding of the problem. At the end of their article, the scientists report that we should not worry about this extremely rare disease. And almost all of us can breathe freely, without fear, and enjoy the pleasant smell after the rain.

sources

Surely, everyone remembers how wonderful the air smells outside after rain. It is clean and fresh. It turns out that this fragrance has its own name and many perfume brands are trying to repeat it.

Grade

The smell in the air that remains after it has rained is called petrichor. The term was coined by two Australian scientists in 1964. Petrikor is a fusion of the Greek words petra (stone) and ichor (ichor - a liquid flowing in the veins of the Greek mythological gods).

In the creation of petrikore, one of the main roles is played by the organic compound geosmin (from the Greek "smell of the earth"). This organic matter is nothing but a waste product of various microorganisms, including cyanobacteria and actinomycetes.

Another scent associated with rain is the smell of ozone. During a thunderstorm, lightning splits hydrogen and nitrogen molecules into the atmosphere, and they are transformed into nitric oxide. This substance reacts with other chemicals in the air to form ozone, which most people like.

If you want to feel the smell of rain not only after a thunderstorm, but every time you wish, we offer a list of fragrances whose manufacturers have tried to replicate this fresh fragrance.

Perfume "Rain" by Demeter

Perfume "Rain" is one of the "cleanest" fragrances in the brand's huge aromatheque. Demeter composers have tried to embody your wettest and most vivid memories of summer rain. Approximate cost - 35 USD.

Like a Walk in the Summer Rain by Essence

"Like a Walk in the Summer Rain" is a floral aquatic fragrance. The perfume composition opens with notes of citrus, orange, aldehyde, cycloclamen and watermelon. In the heart - freesia, lily of the valley, sea ​​water and floral notes. In the loop - musk, oakmoss and white cedar. Specify the cost.

Rainy London fragrance collection by Jo Malone

The collection of fragrances "Rainy London" consists of four bottles. Rain & Angelica with notes of angelica and lime is rain at dawn in a city park. Composition of violet and water lily Wisteria & Violet - cascades of water washing lilac flowers wisteria on the walls. Cumin-cedar Black Cedarwood & Juniper - midnight shower. White Jasmine & Mint with notes of jasmine, mint and mate - a blooming garden washed by jets of water. Approximate cost - 100 USD.

Rain fragrance by Marc Jacobs

Aquatic aroma "Rain" opens with notes of freshly cut grass, notes of wild strawberry and tangerine zest. In the heart of the perfume is a rich combination of notes of tropical rain, passionflower and white orchid. The base notes of beech, tree moss and musk. Approximate cost - from 60 USD.

Endlessly Blue by Tommy Hilfiger

Endlessly Blue is a fresh floral fragrance where water, rain, wet leaves, grass and flowers are the main theme. The composition opens with notes of lemon, white tea, black currant and freesia. In the heart of the fragrance are yellow peony and hydrangea, and in the base are oleander, musk and amber. Specify the cost.