5 Ways Your Nose Lies to You About Danger
Your sense of smell is how you use chemical transmissions to spot threats. Smell a rotting corpse? That’s something you don’t want to eat. Smell a pile of excrement? That’s also something don’t want to eat.
Those last two aversions, by the way, aren’t learned — you’re born with them. With most other smells, we do have to learn what they mean, until we come to associate them with their sources. The odd thing is, we often have no idea exactly what we’re smelling. The real source may be much grosser than you’re picturing.
That’s Not the Clean Scent of Fresh Rain. That’s Millions of Germs Breeding
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The smell of rain on grass or a forest feels deeply comforting, assuming you’re somewhere safe and dry. It even has a name: petrichor. The petr- in that word means “stone,” while the ichor is ichor, the blood of monsters and gods. The name indicates something a lot more hardcore than a gentle nature scene.
Petrichor combines a few different components. You might be smelling ozone, created in a thunderstorm. You’re probably smelling oils that have released by plants. But there’s also a third component called geosmin. This comes not from the rain (which smells of nothing) or from the plants, but from bacteria in the soil.
These bacteria, called actinomycetes, reproduce using spores, and when rain hits the ground after a dry spell, the spores fly up, sending the geosmin through the air. So, breathe in deep the smell of germs. It’s not as harmful as that shitty corpse that your nose is warning you off, but it’s the same basic kind of organism.
That’s Not Chlorine You’re Smelling in the Pool. Somebody Peed
You think you know the smell of chlorine, thanks to public pools, but you don’t.
First off, the chemical that people add to pools to keep it clean isn’t chlorine. It’s some compound of chlorine, such as calcium hypochlorite. You’re welcome to call it “chlorine” informally, just as you’re welcome to call sodium chloride “sodium,” but that’s not what it is. Chlorine is a poisonous gas. If you’re smelling literal chlorine, either someone mixed chemicals wrongly or you’re the victim of a war crime. Either way, you’re in extreme danger.
So, pools are cleaned with something like calcium hypochlorite — but that’s not what you’re smelling when you pick up a “chlorine smell” at the pool. Those cleaning chemicals, dissolved in pool water, don’t smell of anything.
You’re instead smelling chloramines, which is what forms when those chlorite compounds react with some sort of organic matter. It means the chemical reacted to someone’s sweat or possibly someone’s diarrhea, but most likely someone’s pee. A pool that smells strongly of “chlorine” seems like it’s especially clean, but that’s one pool you know is dirty.
If you’re thinking to yourself, “Wait, but every pool I’ve ever been to has smelled of chlorine,” we have some bad news for you about the pee-content of every pool you’ve ever been to.
The Smell of Freshly Cut Grass Is Your Terrified Lawn Calling for Help
Here’s another smell that feels deliciously clean. The smell of cut grass is the smell of nature, as well as the smell of a job well done. Though, when you think about it, you’re smelling plant blood and guts, and that’s kind of gross, right?
Just kidding — that’s a stupid idea. Plants don’t have blood and guts. Apple juice isn’t tree blood, so grass juice isn’t lawn blood. There’s nothing to feel weird about when you smell diced-up vegetable matter.
But that scent that you smell after a lawn is cut isn’t just diced-up grass. You’re smelling compounds called green leaf volatiles (GLVs) that grass synthesizes when attacked.
GLVs do nothing for the grass you just chopped. When other blades of grass detect that compound, however, they respond by bolstering their own repair mechanisms to prepare to be attacked next. Some plants further respond to GLVs by creating new chemicals to temporary become less palatable, so any animal that’s chomping its way through the plants may discover that later plants taste bad and leave.
When you smell freshly cut grass, you’re smelling a distress signal being sent from one plant to another. Unfortunately for the plant, it’s not a very effective distress signal. Some animals have evolved to be attracted to GLVs — and anyway, there’s no repair mechanism that can shield grass from your blade.
There’s No Such Thing as a Metallic Smell. You’re Just Smelling B.O.
You think you know what a metallic smell is. A handful of coins might smell of metal, as might a rusty railing or a box of screws. But steel has no smell at all, and neither does iron oxide.
Instead, much like pool water, what you think of as smelly metal is really the smell of a reaction with organic compounds. Clean coins don’t smell, but a coin in someone’s hand may smell because acid from skin reacts with carbon and phosphorous impurities in the metal, producing organophosphines. For example, you might be smelling 1-octen-3-one, which you think of as the smell of iron but contains no iron at all.
The exact smell of any metal depends on the person who touched it. So, when someone hands you anything that’s metal, you’re not smelling the metal. You’re smelling their body odor.
Natural Gas Doesn’t Smell of Anything
You know the smell of methane if you’ve cooked with gas. It’s an extremely useful scent to know, as it tells you when you left the gas on, which alerts you to turn it off and turn the exhaust on before immediately lighting a match. But methane, like so many gases, is odorless. You’re instead smelling a substance called mercaptan, which is added to the methane very purposely so you’ll be able to detect it.
Gas wasn’t always sold scented. If we go back a century, methane wasn’t sold at all. Natural gas was a waste product that was burned off at the source while drillers extracted the far more valuable oil. The only people who used gas for heating or lighting were those who lived right next to an oil site. In 1937, the London School in Texas was one of those rare buildings to live next to such a site, so it tapped gas right from the company’s waste pipe and used it in dozens of heaters.
On March 18th, a spark lit a leaky gas line, possibly originating from a sander in shop class. The entire school building exploded. The blast killed 294 people (and possibly more), making it the deadliest school disaster in American history, deadlier than any school shooting by a factor of almost 10.
via Wiki Commons
When we got around to commercializing natural gas, we very much remembered the London School explosion (which later became known as the New London School explosion, after the town changed its name). People needed to be able to detect leaks of this gas. So, companies added an odorant, a compound that can be smelled even at tiny concentrations.
The odorant is ethyl mercaptan, an organic sulfur compound. It just so happens to also be one of several compounds that give farts their smell. When you next open the gas at your stove, don’t say to yourself, “Hey, that’s methane.” Say, “Ah! Farts.” And stay vigilant.
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