Adam - 2-5-2004 at 20:20
I don’t have a lab or anything ore than a chem 10 education on the subject so I thought id as you guys. What makes that smell after a heavy rain? I
think its ozone but I’m clearly not sure. And is there a way I could make the smell artificially? To me that stuff is like aromatherapy.
thunderfvck - 2-5-2004 at 20:57
I don't think there's one particular smell, I think it's a whole bunch of smells. Like the smell of the soil, trees, grass, etc.
wettened by the rain.
This isn't organic chemistry.....
Hermes_Trismegistus - 2-5-2004 at 21:21
But I think that the answer lies in botany.
Having had several years experience of the unguided study of the science of plants, I will hazard a guess.
When it rains, all plants want to get in on the bounty, not only does rain bring water, but after a dry spell, the essential nutrient salts are quite
concentrated in the first bit of water that runs to the roots.
To suck up this bounty, the plant actually has to first release water, it is water evaprating out of the stomatae in the foliage that wicks water up
from the roots.
So, to give this water up, and get more, plants will actually dehydrate thier tissues and evaporate off their fluids, contained in those fluids are
various essential oils and many other metabolic wastes at a very concentrated level.
I propose that it is those substances that give the air its smell.
It's the perfume of various plants.
To perform a crude test this hypothesis, I propose a measure of the smell after a long drought, verses a rainfall that follows another recent
rainfall.
I beleive that the air following the rain after the drought would smell much more strongly than that following the more recent rain.
Good luck
DDTea - 3-5-2004 at 02:30
Interesting ideas, Hermes...but your idea for experimentation seems too uncontrolled. Similar to Hermes' idea, you could buy a cheap plant from
the super market, thoroughly dehydrate it, and then come back and water it. This would then be repeated with a hydrated plant. Naturally, you would
be testing which one had the stronger smell...
Ideally, this would be done with 2 plants and the watering would be done at the same time, so you don't forget the strength of one when you are
ready to smell the other.
vulture - 3-5-2004 at 10:59
You have to distinguish between rainfall without lightning and rainfall with lightning though.
unionised - 3-5-2004 at 12:06
I think that at least part of the smell (the wet earth bit, if that makes sense) is a fungal metabolite called geosmin. (which, with blinding
originality, is named after the greek for earth and smell). I think there is some camphor/ borneol derivative in there too.
(from my recolection of an article in new scientist IIRC)
steam distillation effect?
Magpie - 3-5-2004 at 18:05
I've always thought that the rain mixed with insoluble plant oils making them more volatille as with steam distillation.
There are likely other reasons such as gases dissolved in the rain as others have noted.
Adam - 3-5-2004 at 20:41
Well it’s too bad I was hopeing it was a chemical but I guess your answers/ideas make more sense. Still science it the truth not what you want to
make of it... 
Tacho - 4-5-2004 at 03:44
Do a search here on "smell of rain" or "rain smell" using the "Search only in sci.chem" option. There are, at least, two
threads that are very datailed and interesting.
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&group=sci.chem