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(I know little science so please help me if I'm in the wrong place or if my question needs editing. I could use help with tagging, for example.)

If I can smell something then does that mean there are particles or chemicals in the air?

My question is motivated by some new window blinds that have been installed in my home. The blinds have a smell, which is most noticeable when the sun is shining on them. I am trying to work out if the blinds are emitting some chemical into the air. This question is my first step.

[This question is not the same as "How does the smell of a compound come about, and is it possible to define a smell?". This is clear from the title.]

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    $\begingroup$ Followup question: Why can some dry objects (rocks and metal pieces for example) have a smell and not slowly lose mass and vanish, unless they are catalytic and doing something to materials in the air? $\endgroup$
    – rackandboneman
    Dec 3, 2018 at 14:57
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    $\begingroup$ Yes, next time you sniff something in the elevator consider exactly where each of those particles came from--and in order to smell something I don't think we're talking one or two particles--probably thousands? Millions? $\endgroup$
    – Bill K
    Dec 3, 2018 at 16:47
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    $\begingroup$ @rackandboneman Who says they aren't slowly losing mass and vanishing? "Slowly" could easily be over the course of centuries or decades. $\endgroup$
    – anon
    Dec 3, 2018 at 17:38
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    $\begingroup$ Note that "chemical" is a term that's often used somewhat pejoratively. Sure, when you smell bleach or petrol fumes, you're smelling chemicals. But everything is a chemical, so the same is true when you're smelling lemons or baking bread. $\endgroup$
    – David Richerby
    Dec 3, 2018 at 22:16
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    $\begingroup$ You're detecting some kind of off-gassing, which is also known by the prettier name "new car smell" $\endgroup$
    – Criggie
    Dec 4, 2018 at 0:57

3 Answers 3

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Smell works because your nose detects substances in the air.

Everything you can smell is the result of a molecule carried by air interacting with complex proteins in the nose/mouth (smell and taste are related but taste copes with solids and liquids as well as volatile airborne stuff). We broadly understand how smell works but the exact details are often a complete mystery.

The key is that smell-sensing nerves contain some proteins with very specific sensor sites that can detect particular groups of substances when they "fit" into the site. Exactly how the sites translate the fit into nerve signals is often a mystery. But the point that matters for this question is that the stuff being detected has to be carried into the nose via the air (which means it has to be a gas or, possibly, a very small particle that is easily carried by air).

So, yes, smell implies there are chemicals or particles in the air. However, the nose is extremely sensitive to some chemicals and being able to detect the smell does not imply a problem (even nasties like hydrogen sulphide are detectable by smell at below parts per billion concentration, hundreds of times below the level causing harm). Your blinds probably are emitting something but it is most likely both harmless and will probably fade with time like the smell characteristic of a new car.

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    $\begingroup$ "Your blinds probably are emitting something but it is is both harmless and will probably fade with time like the smell characteristic of a new car." - How do you know it is harmless? $\endgroup$
    – cja
    Dec 3, 2018 at 13:33
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    $\begingroup$ @cja I can't prove it is harmless. But your blinds are a consumer product and most likely made from a standard substance (maybe PVC) which has been widely used for decades. Consumer regulations are not perfect but limit dangerous substances in consumer products. And, if harmful things were emitted, lots of people would have noticed by now. $\endgroup$
    – matt_black
    Dec 3, 2018 at 13:37
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    $\begingroup$ Odor from a material such as PVC is generally not the resin itself, but the plasticizer chemical that is used to make the material less rigid. There are also additives for UV resistance and fire resistance. Some of the additives have been proven to be harmful and have been eliminated in some or all jurisdictions. "Additive" sounds like it's a small thing but plasticizers can make up a significant percentage of the total material. $\endgroup$
    – Spehro Pefhany
    Dec 3, 2018 at 14:21
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    $\begingroup$ So, technically this is not 100% correct. Smell implies that there is a signal in the part of your brain that processes smells. Most commonly, this is due to neural input from the nose, but not always, e.g., when someone has a stroke. $\endgroup$
    – Zhe
    Dec 3, 2018 at 15:18
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    $\begingroup$ @cja Also, since every smell is caused by some airborne substance, you can't conclude from a smell alone that there is a harmful substance. Otherwise, every smell would be cause for concern. (Neither can you conclude from the absence of smell that there is no harmful substance in the air. E.g. carbon monoxide is completely odorless.) If you know the smell of a particular toxic substance, that's different of course. $\endgroup$
    – henning
    Dec 3, 2018 at 17:02
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Definitively yes, as already described by another user. I would point out that air conditions, such a temperature and humidity might trigger a kind of smelling sensation in many subjects. The so called "smell of coming snow" is likely an example. It is not related to your windows but I wanted to add this as a curiosity. Very very strictly speaking, smelling something doesn't implies specific molecules or particles are in the air.

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Most definitely you are "smelling" a chemical (almost certainly a gas in this case), and many people have over sensitive inflammatory reactions to many "approved" chemicals in the environment (ie perfumes, fabric softeners, solvents, etc.), so you may have a reaction (like bronchial constriction) even though most people would not.

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