What causes the smell that comes after rain on a hot day?

Answer 1

As it turns out, the smells people associate with rainstorms can be caused by a number of things. One of the more pleasant rain smells, the one we often notice in the woods, is actually caused by bacteria! Actinomycetes, a type of filamentous bacteria, grow in soil when conditions are damp and warm. When the soil dries out, the bacteria produces geosmin spores in the soil. When the soil is too hot, the bacteria are not able to tolerate the dessication, so it produces spores as survival strategies. The spores remain invulnerable for years and are resistant to dessication and heat. The wetness and force of rainfall kick these tiny spores up into the air where the moisture after a rain acts as an aerosol (just like an aerosol air freshener). The moist air easily carries the spores to us so we breathe them in. These spores have a distinctive, earthy smell we often associate with rainfall. Geosmine (dimethyl-9-decalols) is the microbial product found in the spores is responsible for this pleasant smell.

Another sort of smell is caused by the acidity of rain. Because of chemicals in the atmosphere, rainwater tends to be somewhat 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. These reactions generally produce more unpleasant smells than bacteria spores, which is why the after-the-rain smell isn't always a good one.

Another after-the-rain smell comes from volatile oils that plants and trees release. The oil then collects on surfaces such as rocks. The rain reacts with the oil on the rocks and carries it as a gas through the air. This scent is like the bacteria spores in that most people consider it a pleasant, fresh smell.♥

Answer 2

a million. hour of darkness Horror Afternoon delight 2. Sucking out the Air respiratory in the water 3. Monday nighttime Sunday morning 4. Water Salt Virgin Nature (Ugggh...this one FAILS) 5. strolling off Rain Clouds engaged on... 6. He Yells at Demons She whispers at angels 7. Dim Off Me Sane Coal 8. previously the Silver Dawdle 9. Trusting Human 10. Dim unhappy Animals vibrant chuffed 11. Run Off the Tame suitable walk on the wild area 12. you will snigger (somewhat) We Cry somewhat 13. Apathy for the Angel Care of the devil 14. The Silence of Noise The sound of silence 15. Tastes in assessment to person physique Smells Like teen Spirit - Nirvana sixteen. that's a Demented job of touch-him 17. an trouble-free nighttime's Day a problematic day's nighttime 18. Run, Genius, Run walk fool walk - The Hives 19. existence and None of Her Enemies death and all his buddies 20. bear in innovations Him forget her 21. stumbled on result lost... 22. The wasteland Gasps Sugary the sea something salty? 23. not one of the previous Chicks each and all of the greater youthful dudes 24. There is going the Moon right here Comes The sunlight - The Beatles 25. pink Graphite-worse Orange something better I guess you are able to tell I guessed some.... MQ: Keane - Spiralling <-- solid music :)

Answer 3

Most likely if you live in a city,it is the smell of the asphalt absorbing moisture and releasing gas's due to the increase in humidity.Once the rain begins,the oils within the asphalt rise to the surface,creating that smell that you experience....Tom Science 4

Answer 4

On a really hot day, after the rain, the water begins to evaporate. Part of what you're smelling is the water vapor. I imagine that if the pollen is high, that some of that will be borne on the water vapor, and you could be smeling that as well.

Answer 5

The smell of rain is caused by ozone (O3). It is commonly produced through dissociation of molecular oxygen (02) into two unstable atomic oxygens (2 O), each of which then recombine with molecular oxygen to make ozone.

This dissociation can occur either by high-voltage electrical discharge or by bombardment with ultraviolet light. The high voltages which occur in thunderstorms create ozone within the cloud (even when lightning is not actively occuring), and this ozone is carried toward the ground by the downdraft in the thundercloud and blown out ahead of the storm, where you smell it and can tell rain is coming.

Ozone is also created high in the stratosphere by ultraviolet light: this is the "ozone layer" which protects us from harmful UV light.

A third place you're likely to find ozone is coming out of your photocopier or laser printer. These devices have high-voltage discharges inside them, and produce enough ozone to bother me while I'm sitting here next to one typing this.

Why would water on asphalt generate ozone? I don't think it would. But I've noticed the smell of water-on-pavement you're talking about, and I do associate it with rain. Your sense of smell is very evocative: it can bring very vivid memories associated with smells. My theory is that there are two different smells associated with rain: the ozone smell before it starts raining, and the "pavement" smell once the rain begins falling on the pavement. Either one will make you think of rain, and they probably get mixed in your mind.

So what is that smell produced by wet concrete? I honestly don't know, but It's similar to the smell of freshly-mixed concrete, and I've also smelled it when carrying out the reaction

Ca(OH)2 + CO2 -> CaCO3 + H2O

Some rocks (limestone?) also smell like this when wet. I suspect the smell has something to do with calcium; either small particles are released into the air which enter your nose, or there's some sort of gaseous calcium-containing molecule produced by interaction between carbon dioxide, water, and a calcium compound (though that seems unlikely.)

Answer 6

No scientific answer sorry, but when it rains here and you can smell wet dust and eucalypt.....you're not too worried about the cause, and never would it be classed as a smell.

Answer 7

someone told me its the high ozone content of the air.. I dont know, but it always has this metalic watery smell..