When it rains after a prolonged period of dry weather, there is a smell created. It's called Petrichor. A wonderful word, and utterly useless trivia item. The smell is caused by something call Geosmin, which is produced by bacteria in the soil. Humans can smell it at 5 parts per TRILLION. In contrast Sharks can detect blood at concentrations of 1 part per million. On this one substance, we have a better sense of smell than sharks do for blood. Humans are amazing!
@quixoticgeek
It is a wonderful word, and phenomenon.
The generation of petrichor was first described by Australian scientists Isabel (Joy) Bear and Richard Thomas in Nature journal in 1964. They were working for the national scientific and industrial organisation (the CSIRO) at the time.
@quixoticgeek
I'd wager most humans can't smell Geosmin at anything like 0.000005 ppm due to being overwhelmed by laundry detergent and other perfumes at much higher concentrations.
@fragrancesensitive That would only be the case if the receptor for Geosmin is the same as that used by Laundry detergent perfume. I agree that we are exposed to a lot of pollutants that overwehelm our olfactory system, but I think laundry detergent is not in the top 10. Car exhausts would be near the top tho.
@quixoticgeek
Given that detergent (+ other product) perfumes can be quite overwhelming, I wonder how many receptors they target. but I'm not expert with the biological smell receptors. Can one absolutely say what the top ten olfactory contaminants are? It would depend very much on where you take samples. In a car dense city, or a small almost car free village where everybody hangs laundry out on the balcony. Empirically, domestic product perfumes are in some people's top 10 for sure.
@quixoticgeek
I would also suggest that car exhausts tend to be non constant. It does depend on local laws, but many places now have quite high controls on exhaust emissions. Even if a particularly contaminating vehicle were to pass one by, the resulted pollutant will disperse within a few minutes. This is not the case for people who walk around all day (and sleep all night) immersed in a cloud of off-gassing from their products.
@fragrancesensitive Erm. That's an interesting theory. It's nuts, but hey if you're happy.
I can smell the pollution from cars in the city. Even at night when there aren't many cars around. It lingers. Far more than the "off-gassing" of my bed sheets or t-shirts.
@fragrancesensitive More people live in those car soaked hell holes, than the idyllic villages where everyone air dries their laundry...
I have to say having grown up with the laundry being hung out to dry in the garden being the norm, I've never knowingly smelt the laundry detergent. Maybe cos I could only smell the grass, trees, flowers, etc...
@quixoticgeek
If you have any scientific insight into why some people are sensitive to modern perfume products and others are not, it would be nice if you could share it. Research on smell receptor variations, that kind of thing.
@fragrancesensitive I do not. It's something that is entirely new to me. I only discovered it existed recently when I purchased the wrong laundry detergent, buying a "zero odour" product that did not remove the smell from my clothes. They smelt just as sweaty after the wash as they did before. What I do know is that the "zero fragrance" products actually require chemicals to counter the natural odours of the washing chemicals. So the're still off gassing.
@quixoticgeek I love the smell after rain. #Petrichor is a word I learned in school that actually stuck. It suddenly boomed around the mid-90s when it was appearing in everything.
@quixoticgeek@yogthos anyone have any idea what evolutionary advantage being able to detect petrichor at these levels provides? WHY can we smell it that well?
@quixoticgeek Every time I hear that word, all I can think of is that Doctor Who episode where Petrichor--or rather, the thought of what it means--is part of a password. That's where I learned what that word means. Who says sci-fi isn't educational?
@filobus you're on the savanna. It's not rained in a moon. And then you smell something. Something on the wind. Maybe that way to fresh grass and hopefully something to hunt...
@quixoticgeek@vicgrinberg Super interesting. At first I thought it was going to be about how bad NYC smells after rain because garbage smell goes everywhere. 😂
@quixoticgeek If you're a nomadic herder or hunter, it would be super useful to be able to say "Hey, if we head upwind, we'll get to an area where it just rained and the grass is about to sprout!" Wonder if grazers/browsers have the same sensitivity?
@quixoticgeek There's also Dimethyl sulfide which provides the smell of the sea, which is flamable. detectable at 0.02 to 0.1ppm and associated to cabbage. The ocean smells like cabbage! 😁
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