Petrichor: why does rain smell so good? | Hacker News Reader

Petrichor: why does rain smell so good?

bbc.com

206 pointshappy-go-lucky34 comments

Another interesting chemical interaction is how lightning causes rain to be more nourishing to plants. It separates the nitrogen from the air, which combines with oxygen to form nitrogen dioxide. "Nitrogen dioxide dissolves in water, creating nitric acid, which forms nitrates. The nitrates fall to the ground in raindrops and seep into the soil in a form that can be absorbed by plants." --- https://wxguys.ssec.wisc.edu/2018/07/09/lightning/

This has been folk knowledge in Japan for thousands of years. Rice paddies are traditionally planted in places with a propensity to lightning storms, a fact so well known that it reduces land values in suburbs built on old paddy land (there are other downsides to that land, but this is one).

Also, the word for "thunder" (雷) is written as "rain" (雨) over a "rice paddy" (田), and the word for "lightning" (稲妻) is "rice plant's (稲) wife (妻)".

Off topic but do you have a resource for your second paragraph? I find this etymology fascinating!

Not sure if this is what you had in mind, but, for example:

rain - https://ja.wikipedia.org/wiki/雨

field - https://ja.wikipedia.org/wiki/田

thunder - https://ja.wikipedia.org/wiki/雷

rice - https://ja.wikipedia.org/wiki/稲

wife - https://ja.wikipedia.org/wiki/妻

lightning - http://nihongo.monash.edu/cgi-bin/wwwjdic?1MDJ%B0%F0%BA%CA

Those would probably be more helpful as Wiktionary links:

rain - https://en.wiktionary.org/wiki/雨

field - https://en.wiktionary.org/wiki/田

thunder - https://en.wiktionary.org/wiki/雷

Note that the "glyph origin" section describes 雷 as an ancient simplification of the phono-semantic compound 靁, where 畾 indicates the pronunciation. Any relation to rice paddies is probably a post-hoc rationalization.

rice - https://en.wiktionary.org/wiki/稲

wife - https://en.wiktionary.org/wiki/妻

lightning - https://en.wiktionary.org/wiki/稲妻

This is actually common, folks think Kanji are random strokes, but they tell stories and tend to make sense. Understanding the relations makes it easy to remember.

Hey, do you know about what scent is used in mineral water in Japan. Our friend gave us some last year and we were amazed how primal and fresh it smelled, trying to trace it all the time.

From the description it could be petrichor, but we had this similar smell once coming off ocean island once (Kawau, NZ) so we not sure

Curious to know what mineral water you are speaking about

On mobile, but they also nailed lightning helping mushrooms grow.

https://phys.org/news/2010-04-lightning-mushrooms.amp

Amazing. Here’s a newer research that unveiled the cause is cuts and scratches inside https://api.intechopen.com/chapter/pdf-download/62393

I'm usually a lurker and rarely comment but yours was such a nice little informal comment that I had to say something. Thanks for bringing a smile to my face :)

Nice! And speaking of etymology, my favourite trivia from the article: The word was coined from Greek petros, meaning "stone", and ichor, meaning "the fluid that flows in the veins of the gods". I always wondered what the second half meant.

I think it's common knowledge that rain water is excellent for plants. But I don't think many people know the mechanism of action. Although I suspected water somehow picked up nitrogen in the air, I wasn't aware exactly how. Thank you for sharing!

In the modern era, nitrogen dioxide is a pollutant; it's also produced by most combustion processes. Too much of it results in "acid rain" which is harmful to plants.

Can't have too much or too little.

Lol this reminds me of what my dietitian cousin is known to say: everything in moderation... including moderation ; )

The best rain smell is in the southwestern US like New Mexico and Arizona. The creosote bushes all release their scent into the air and it's the most refreshing thing ever. It's worth visiting the area for a few weeks during Monsoon season just to get a chance at experiencing this. You have to be near the desert though, not in an urban area.

The western US desert in the rain definitely has a lovely smell to it that is almost therapeutic. It is interesting how distinctive the smell is of various wilderness areas of the US, especially after rain.

As someone who grew up in the rural Pacific Northwest of the US as a child and moved back there much later in life, I realized that I find the unique smell of the Cascade mountains to be irrationally relaxing. I've always wondered what, specifically, makes me respond to it that way.

For what it's worth, I grew up in Pennsylvania, and when visiting home, I found the keystone shaped state route number signs irrationally relaxing. I'd guess the reason is, you remember the smell from your childhood.

I haven't been there so I can't compare, but my favourite is in Lithuania where the country has a large nunber of pine forests. After the rain you get a lovely smell of pine in the air. Even on the outskirts of the city and the airport you can smell it, not just far away. I remember once I travelled here from Italy, and just stepping off the plane I though "wow it smells so good".

The pine scent may actually be "terpenes": "Often the plant chemicals that smell pleasant are produced in leaf hairs... and the rain may damage these, releasing the compounds."

I feel like there have been many discussions of this over the years but found only one, from 2013:

https://news.ycombinator.com/item?id=5583575

Nothing beats the smell of the Sonoran desert during the rain, thanks to a special plant called the Creosote bush. Rain is also rare enough so everyone from the region grows to appreciate it a lot.

I was going to say... having grown up in western Oregon, I think rain smells good when it's not an everyday occurrence for months on end!

I am so bummed that Geosmin is so expensive. Almost $600 for 10 milligrams! https://www.sigmaaldrich.com/catalog/product/sigma/uc18?lang...

"If not today then soon, gray clouds will gather. Let it come so I might hear leaf splats, watch the wet blotch, taste on my tongue, feel on my face the pentecost of petrichor." --Above the Waterfall, Ron Rash

This is one of my favorite words.

The article is a good summary of what produces the smell, but why do humans tend to find it appealing? Is it wired into our collective subconscious?

Seems reasonable. If I put on my ad-hoc explanation hat, since geoosmin is produced when Streptomyces die, tasting it in water might indicate that the ecosystem is under stress. Conversely, smelling it in the air suggests that the soil ecology is healthy -> good place to plant crops.

I have an old book by Magnus Pyke called "Butter Side Up" which has a chapter on this. The bit about Streptomyces wasn't known then though. https://en.wikipedia.org/wiki/Magnus_Pyke https://www.amazon.co.uk/Butter-Side-Up-Delights-Science/dp/...

About 30 years ago I saw “The Five Doctors” (the 25th anniversary episode of Doctor Who). Ever since then I’ve believed the smell, and associated feeling, were due to “positive ions”. In all that time I’ve never fact checked that line, but I think about it every time I notice the smell after a storm.

From the screenplay: TURLOUGH: It's marvellous here. I feel so calm and relaxed. DOCTOR 5: It's the high bombardment of positive ions. TEGAN: It's like Earth after a thunderstorm. DOCTOR 5: Same cause and reason.

My fave song about petrichor is by Paul Kelly: https://youtu.be/A9_qkTeMlGk

If you find the article interesting you will most likely want to enjoy it to Ludovico Einaudi's sublime Petricor piece (modern violin / cello / piano). Its a beautiful piece of music.

https://open.spotify.com/track/4XWqS8UGO5x4ClB2yH0nbW?si=Ewz...

And congrats on the good taste, even if I say so myself.

I read a book that talked about how negative ion environments make you feel better. I believe Nikola Tesla even wrote about this while experimenting with some device that created negative ions. Places like niagara falls and natural water-related environments (waterfalls, riversides, beaches) have some of the highest negative ion concentrations while air conditioned environments have some of the lowest.

I've always wondered about this smell. What about the small of freshly cut grass?

Good????? That smell is absolutely disgusting and I have to actively avoid breathing through my nose.

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