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Author Topic: Why does the air smell after it rains?  (Read 44598 times)

Offline neilep

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Why does the air smell after it rains?
« on: 18/09/2006 20:08:10 »
But why does the air smell nice after it has rained?...it's kind of refreshing!

Is it to do with a load of positive ions ?...or is that something entirely different that gives you a sense of well being after a thunder storm?

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« Last Edit: 14/06/2009 09:38:07 by chris »


 

Offline Karen W.

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Re: Why does the air smell after it rains?
« Reply #1 on: 19/09/2006 01:50:33 »
I always thought it was because it washed all the dust and particals away and gave everything that just washed fresh!!I really don't know why it really smells good!

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another_someone

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Re: Why does the air smell after it rains?
« Reply #2 on: 19/09/2006 11:45:44 »
If the rain comes after a dry spell, it could be just the smells given off by the vegetation in response to the rain.

I think also that our noses become more sensitive in moist environments as the drops of moisture will be trapped in our noses, giving a better chance for the nose to detect any chemicals that are contained within that moisture.



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Offline Karen W.

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Re: Why does the air smell after it rains?
« Reply #3 on: 20/09/2006 08:22:33 »
That's interesting and makes sense.  Here in California, It gets really dry inthe summer and thier is lots of dust as cars travel up our dry gravel road. Like  dustbowl. So when the first rain you get a very strong earthy wet dirt smell, once it soaks in a bit and really rains you can smell the other stuff.. plants etc, feels and smells fresh then!

Karen
« Last Edit: 01/10/2006 23:00:52 by Karen W. »
 

Offline jysk

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Re: Why does the air smell after it rains?
« Reply #4 on: 30/09/2006 19:00:56 »
The nice smell that I'm thinking of is strongest just as a rain shower is beginning. It can be quite strong as the first drops are hitting the ground and still more intense if preceeded by warm sunshine. The smell always takes me straight back to a game of marbles I was playing 35 years ago in my school yard.

I understand that this "fresh and clean" smell is in fact, ground-level ozone. The irony is that is it's mildly toxic rather then cleansing.

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another_someone

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Re: Why does the air smell after it rains?
« Reply #5 on: 01/10/2006 23:13:34 »
quote:
Originally posted by jysk
I understand that this "fresh and clean" smell is in fact, ground-level ozone. The irony is that is it's mildly toxic rather then cleansing.



No, ozone is not “mildly toxic rather then cleansing “, but is cleansing precisely because it is toxic.  In some cases, ozone is used in place of chlorine to disinfect water, and it is probably less toxic than chlorine (as well as quickly converting to diatomic oxygen, that being both its strength and its weakness as a disinfectant).



George
 

Offline Hadrian

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Re: Why does the air smell after it rains?
« Reply #6 on: 02/10/2006 19:02:45 »
I think perhaps there could be enzymes released from the earth too and this would also contribute to the smell. Now it just a idea OK so don’t sue me or anything. [^]

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Offline Atomic-S

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Re: Why does the air smell after it rains?
« Reply #7 on: 11/10/2006 05:38:37 »
Well, I don't know definitely everything about the smell of rain, but one factor that does exist is that during such weather, certain plants tend to odoriferate, notably the creosote bush of Arizona, which inparts a bracing spicy freshness to the air at certain times. Other plants have also been noted; spraying arbor vitae with a hose will make it smell somewhat piney (during dry weather). As for the ozone, maybe that is the key regarding the specific smells right before rain starts. I would not know.
 

paul.fr

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Re: Why does the air smell after it rains?
« Reply #8 on: 21/03/2007 09:46:34 »
this was from random post generator:

the smell after rain is actually the smell of bacteria – actinomycetes – they grow world-wide in damp soil. When the soil dries out, they die. But before they die, they make spores. These spores are really tough and can survive dry conditions for years. When the raindrops hit the ground, they make a mist of water and dirt, which you both breathe in and smell
« Last Edit: 21/03/2007 10:04:20 by paul.fr »
 

Offline Karen W.

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Re: Why does the air smell after it rains?
« Reply #9 on: 22/03/2007 01:44:02 »
That is interesting. Cool!
 

Offline chris

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Why does the air smell after it rains?
« Reply #10 on: 14/06/2009 09:48:40 »
The characteristic smell in the air that follows a recent shower is down to bacteria. These didn't come down in the last shower (!) but instead they're a family of ubiquitous filamentous soil-dwellers called the actinomycetes. This bacterial species make tiny "spores", which are metabolically inert or dormant forms of the bacteria and which remain resident in the soil when the ground dries out.

The purpose of these spores is to enable the organism to survive dessication and other severe conditions for extended periods of time. When it rains the water hitting the ground ejects millions of them into the air where they drift up peoples' noses, contributing to the fresh and earthy smell of a recent shower.

As a rule they don't pose a threat to humans - at least not to people with a healthy immune system - and making the air smell is not their primary goal. What will actually happen shortly after the shower is that the newly uncovered and dampened spores will settle back onto the ground and germinate. So you could look upon this process as part of the way that they disperse and spread themselves around the planet.

Chris

[This question has been answered by others above, including Paul (thanks). The purpose of this post is to draw strands together and give a thorough answer.]
« Last Edit: 14/06/2009 09:51:12 by chris »
 

Offline Don_1

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Why does the air smell after it rains?
« Reply #11 on: 15/06/2009 09:28:12 »
In addition to these bacteria, there are also a number of leaves which release scent when touched. This can be triggered by heavy water droplets in rain.

e.g. Lemon Balm and scented pelargoniums. You might need a considerable number of such plants for any scent to be easily noticeable.
 

paul.fr

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Why does the air smell after it rains?
« Reply #12 on: 16/06/2009 19:19:23 »
Lets not forget that the research that found the cause to be actinomycetes was done in the 60's, does anyone know of any updated reasearch?

http://www.thenakedscientists.com/forum/index.php?topic=8054.msg93197#msg93197
Quote
Title:
 Genesis of petrichor
Authors:
 Bear, I. J.; Thomas, R. G.
Publication:
 Geochimica et Cosmochimica Acta, vol. 30, Issue 9, pp.869-879 (GeCoA Homepage)
Publication Date:
 09/1966
Origin:
 ELSEVIER
Bibliographic Code:
 1966GeCoA..30..869B


Abstract
"Petrichor", well known to mineralogists as argillaceous odour, is commonly observed as the pleasant and refreshing odour which frequently accompanies the first rains after a warm dry period. Several possible mechanisms have been considered in connection with the origin of this odour. These include the synthesis of odorous compounds on the clay or rock surface by spontaneous catalysis of atmospheric gases, the sorption of organic compounds from the atmosphere, catalytic transformation of sorbed compounds and microbial activity. Evidence is presented which suggests the atmosphere contains, as general contaminants, lipids, terpenes, carotenoids and other volatile decomposition products from animal and vegetable matter. The sorption of these compounds, or their oxygenated derivatives, by rocks and clays is controlled by the properties of the sorbent and the partial water vapour pressure of the atmosphere, low relative humidities favouring maximum uptake. Oxidation and transformation of sorbates take place on the rock surface and are accelerated by warm to hot climatic conditions. The odorous and volatile products of these processes are subsequently displaced from the pores of the rock by moisture when the relative humidity of the atmosphere approaches saturation. The possibility of a relationship between petrichor and petroleum formation is discussed.

 

Offline Mr. F

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Why does the air smell after it rains?
« Reply #13 on: 18/08/2010 14:30:17 »
It's also possible that the smell is produced by Pseudomonas Syringae:  a bacterium that is linked to rainfall patterns and comes from food crops.
 

Offline tommya300

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Why does the air smell after it rains?
« Reply #14 on: 19/08/2010 04:54:47 »
Can this relate to Why does some rain smell...  But not all... ??

Quote
What does ozone smell like?

Ozone's characteristic odor can be smelled immediately after a lightening storm or near photocopiers and electric motors, all which generate ozone. Its odor has also been described as the smell of clean bed sheets or forest air.

How is ozone formed by nature?

Trees emit hydrocarbons, by-products of photosynthesis; together with sunlight, they produce ozone. The electrical discharge of lightning can also produce ozone. That is why the air always smells so fresh after a thunderstorm and in a forest.



http://www.coleparmer.com/techinfo/techinfo.asp?ID=533&htmlfile=OzoneQ_A.htm

The characteristic smell in the air that follows a recent shower is down to bacteria. These didn't come down in the last shower (!) but instead they're a family of ubiquitous filamentous soil-dwellers called the actinomycetes. This bacterial species make tiny "spores", which are metabolically inert or dormant forms of the bacteria and which remain resident in the soil when the ground dries out.

The purpose of these spores is to enable the organism to survive dessication and other severe conditions for extended periods of time. When it rains the water hitting the ground ejects millions of them into the air where they drift up peoples' noses, contributing to the fresh and earthy smell of a recent shower.

As a rule they don't pose a threat to humans - at least not to people with a healthy immune system - and making the air smell is not their primary goal. What will actually happen shortly after the shower is that the newly uncovered and dampened spores will settle back onto the ground and germinate. So you could look upon this process as part of the way that they disperse and spread themselves around the planet.

Chris

[This question has been answered by others above, including Paul (thanks). The purpose of this post is to draw strands together and give a thorough answer.]

Is that the reason why it sometimes smells like a damp mushroom farming room?
 Or in the better part of the year when picking wild mushrooms?


« Last Edit: 19/08/2010 05:14:46 by tommya300 »
 

Offline Jahnavi

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Why does the air smell after it rains?
« Reply #15 on: 01/10/2010 10:28:31 »
The pleasant earthy smell after the rain has moistened the soil is from the Actinomycete bacteria. These grow as white threads through forest litter and the compost and make that distinctive fresh earth smell when the soil is turned also. When the rain drops hit the soil they splash the Actinomycete spores up so they become air born carrying the scent of geosmin with them.These as a class are our beneficial bacteria that are sources of antibiotics. This has lead to the thought that the reason they smell good is they may be beneficial when inhaled. It has been shown that certain soil bacteria do have positive psychoactive benefits when handled. Mycobacterium vaccae, may increase our serotonin when we handle soil.
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« Last Edit: 01/10/2010 13:53:37 by peppercorn »
 

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Why does the air smell after it rains?
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