The smell of rain

[The Mangler]

What exactly is it that you smell before it rains? Some people say "Are you crazy, you can't smell the rain." But I know the air definatly smells different before it rains (or snows).

[The Mangler]

Nevermind, I found it.
odour of approaching rain

[Gillianren]

I would add that David Feldman (who writes the Imponderables books) says there's no real consensus, and there are a few other options. However, a) I'm not sure which book he says it in, and b) I'm pretty sure quoting all of it would be frowned upon, though it may well be considered fair use legally.

[grant hutchison]

There's also a distinctive smell when rain first falls on dry earth: the word for this is petrichor. A web search for that word might turn up more information about your question, too.

Grant Hutchison

[The Mangler]

From wordsmith.org:

"Petrichor, the name for the smell of rain on dry ground, is from oils given off by vegetation, absorbed onto neighboring surfaces, and released into the air after a first rain." Matthew Bettelheim; Nature's Laboratory; Shasta Parent (Mt Shasta, California); Jan 2002.

[Enzp]

I now smell it when it IS raining, but when I was young I often smelled approaching rain. It baffled my mother. I never saw it as cosmic or even puzzling. That said, I never identified the process.

[The Mangler]

I think that's why animals always know when something bad is going to happen. They can smell it long before it comes.

[Swift]

I think that's why animals always know when something bad is going to happen. They can smell it long before it comes.

So what does a I'm-taking-you-to-the-vet smell like?

[The Mangler]

my sense of smell isn't strong enough for that one, but I would imagine that it doesn't smell good.

[Enzp]

We told the cat he was going to get "tutored," so he cooperated. Later we told it that he simply misunderstood. Never smelled it coming...or going.

[peteshimmon]

When it starts to rain after dry days, I always thought it was a "chalky
earthy" smell. I thought it might be effervesance of carbonates due to
any acidity in the rain. Others think it is a mouldy smell. Looks like it is
the same everywhere not just urban areas.

[publiusr]

WEATHERWISE magazine had a write up on that not long ago.

[Argos]

When it starts to rain after dry days, I always thought it was a "chalky
earthy" smell.

It smells like BHC to me (the herbicide, remember?).

[John_Charles_Webb]

Nevermind, I found it.
odour of approaching rain

The link contains information that is incomplete (ozone).

Negative ions clean the air of dust, dirt and smoke particles. Restoring the air to its (approximate) natural condition. So, the fragrance of rain is the natural (un-polluted) condition of the air.

[snarkophilus]

Nevermind, I found it.
odour of approaching rain

I don't think it's ozone... the ozone smell is that sharp smell associated with lightning. To me, it doesn't seem quite the same as the smell of water on rock, which very close to the smell I always associate with rain (it is my favourite smell... yummy...).

My coffee table is a big slab of shale that I found out in the forest, and I can get that rain smell just by sprinkling some water on it.

Just did an experiment with said table, and here are the results:

The rock alone has a very faint odour, probably due to dust/dirt on the surface. It smells like dust.

After wiping down a bit of rock with the edge of my shirt (which is dry), I notice that the smell is a lot stronger, and sort of resembles the rain smell. It's not quite it, but it's close. Maybe it is a part of the larger smell. Waiting two minutes, I notice that the smell is still there (I checked by first smelling an un-wiped section of the table, then smelling the wiped section, then going back and forth to confirm), but it is very faint.

Pouring a bunch of water on the rock, I notice that there is a strong smell around the edge of the puddle. It's slightly more complex than the wiped-down smell... more mineral, I guess. Not as strong. Two minutes later, the smell is still strong. Five minutes later, it has faded from the edge that is still in the same place. The other edge has receded, and this edge is interesting.

Where the water has receded (evaporation or absorption, I am not sure), the stone is merely wet, but not covered by water. It has a very strong smell, roughly the same in character as the other edges of the puddle, but much stronger.

Spraying a section of table with a squirty bottle makes the whole room smell like it's been raining. It drowns out any other smells, so I can't determine (right now) how quickly the wet area from the original puddle loses its smell.


So, from this, it looks like rock (shale) gives off a strong smell when it is dampened or simply cleaned. Possibly what is happening is an aluminum can-type effect. The surface of the rock is oxidized, but underneath, it is not. When the surface layer is cleaned off, either through abrasion or water carrying it off or whatever, the reduced minerals react and one of two things happens:
1. Something in the air (probably oxygen) reacts with the minerals, leaving free ions (or radicals, perhaps) in the air. A possibility is 2 O2 + mineral --> O3 + mineral-O, which would mean that the ozone hypothesis is right.
2. Something in the air (again, probably oxygen) reacts with the minerals, producing a gas that includes the mineral or a dusty form of the mineral that dissolves in the air. That would account (partly) for the slightly different smell.

The actual rain smell seems more complex than this one, so there is probably a lot more going on. I favour number 2, because it really doesn't smell like ozone, but I'm having trouble deciding how the reaction stops. The fact that it is stronger when water is involved suggests that there is a transport factor... the reaction (if it is a reaction) only occurs continuously when some of the products can be transported away (dissolved into the water). That would be why the smell fades after a while: the water has become saturated, and no more reactant can be carried away.

It would be interesting to see if this was the case, by using different volumes of water with the same contact area, and measuring when each stopped smelling. Maybe I'll suggest it as a science fair project to my little sister or one of her friends....

[The Mangler]

But you can smell the ozone (?) before it rains, so nothing would be wet.

What you describe could possibly explain this:

"Petrichor, the name for the smell of rain on dry ground, is from oils given off by vegetation, absorbed onto neighboring surfaces, and released into the air after a first rain." Matthew Bettelheim; Nature's Laboratory; Shasta Parent (Mt Shasta, California); Jan 2002.

[hippietrekx]

I can smell rain coming. It smells sort of like... Hard to describe... distant mud, I guess. It smells more when it's windy.

And then there's during/after rain smell. Smells like worms to me.

And then there's that cold smell. When it's cold, there's this sort of, not sterile (like a hospital), but clean smell (like the inside of a new appliance). I don't like the smell of cold.

Does anyone else know that cold smell I speak of?

--hipster

[The Mangler]

Smells like worms to me.

That's exactly what I always thought it smelled like. But do worms have a smell? I think you just see worms whenever you smell rain, so you just associate the two and think of worms whenever you smell whatever it really is.

Does anyone else know that cold smell I speak of?

I actually like that smell. It's refreshing. Crisp.

[hippietrekx]

I actually like that smell. It's refreshing. Crisp.

Well, now I know I'm not crazy. Everyone is always like, "How do you *smell* cold?!" I'm not sure what about it bugs me. Sorta like coffee. Most people like the smell but it jsut irritates me. It's not that it smells bad... Yeah, I don't know.

--hipster

[Maksutov]

It's just the rain releasing all the teen spirit that's locked up in the dust.

[The Mangler]

Well, now I know I'm not crazy.

Well, we could both be crazy... Or maybe it's everyone else whose crazy...

[hippietrekx]

Well, we could both be crazy... Or maybe it's everyone else whose crazy...

Ha! It's like George Orwell's 1984! Is Winston crazy or is everyone else? Does sanity lie in the majority?

--hipster

[Gillianren]

If it helps, I can smell cold, too. So-o-o-o much better than the smell of heat, or worse, the smell of a hot and humid day.

[Maksutov]

If it helps, I can smell cold, too. So-o-o-o much better than the smell of heat, or worse, the smell of a hot and humid day.

I agree. Those heat and humidity smells are terrible.

Give me the wonderful aroma of a clear night in northern New England when it's -32. Aahhh!

[trinitree88]

The strong thermals that create the updrafts in thunderstorms bring warm surface air up through the ozone producing clouds. Cooling chills the air condensing it. It spills over and out of the torus...if there's spin involved...mesocyclones roll towards the ground, sometimes forming tornados, but always there are associated downdrafts of cooler-than-surface air due to the density inversion. When they fall in front of the approaching cold front....it bulldozes it along the ground like a big snowplow.....and you can smell the approaching rain. The wind shifts, temp drops, the smell is there....you've got a few minutes to run for cover. Ciao. Pete.

[Gillianren]

I agree. Those heat and humidity smells are terrible.

Give me the wonderful aroma of a clear night in northern New England when it's -32. Aahhh!

I'm rather partial to the smell of a Washington State autumn, myself. Nice and crisp, with an odd little dusty undertone from the falling leaves. Heaven!

[The Mangler]

Ha! It's like George Orwell's 1984! Is Winston crazy or is everyone else? Does sanity lie in the majority?

--hipster

One of my favorite books.

[Swift]

Snarkophilus, that was a great experiment. I have one other thought about shale. Shale is a very porous rock. Many shales have trapped organic materials in them (wikipedia link). There is a shale formation in Ohio called Bedford shale; when you break it open you can often smell an organic, oily smell. Now, I'm not suggesting that is what you are smelling on your table (sound like a neat table by the way), but there could be materials trapped in the shale that are released when you rub it (heating from friction?) or when you put water on it. Could the rain smell be "stuff" released from the dirt and rocks when they are rained on? Would different soils and rocks have different rain smells - if so, there should be a geographic difference in rain smells.

[Gillianren]

Hmmmm.

Well, I've lived roughly two-thirds of my life in LA County, and roughly one-third in Washington State, and I would say the rain-smell in both is approximately the same. However, I think the smell of an Arizona monsoon is different than either, so I'm not sure. Anyone willing to sponsor the travel to find out? I've nothing better to do with my time!