Science Lesson: what are vapor, aerosol, particles, liquids, and such?

by Carl V Phillips

There is much confusion about states of matter as they relate to e-cigarette “vapor”. This post is intended to explain what you need to know about them.

The word “vapor” has become a generally accepted term for “what comes out of an e-cigarette”. That means what it means, and that is fine. Common language often takes technical terms and uses them in a way that is “incorrect” if interpreted as if it were the technical term. But this can create confusion.

Vapor (in the normal sense of the term) refers to the gas phase of something that is “normally” a liquid. So the bits of H2O that evaporate into the air are “water vapor” (not to be confused with fog — keep reading). There is no actual technical definition for what subset of gasses are called vapor. The “normally” in my definition is obviously a fuzzy term that basically means, “in everyday settings, within Earth’s biosphere, in non-extreme weather, it is a liquid (e.g., water, ethanol, propylene glycol, to name a few favorites) but the particular molecules in question are in gas phase.” (I found a nice exposition of this “normally a liquid” point here if you are interested.)

Let me step back a second: Any chemical can be in gas, liquid, or solid phase, depending on the temperature and pressure. These are defined as follows (phrased casually, but basically the technical definitions): Solid is the phase in which something maintains its shape rather than conforming to the space it occupies; the molecules of a solid mass mostly stay where they are in relation to each other. Anything that is not a solid is a fluid, which means that the molecules move freely with respect to each other, which produces the notable feature that it conforms to the shape of the space it occupies. That word is often misused as if it means “liquid”, but it actually means “liquid or gas”. A gas is a fluid where the molecules are separated across a lot of space and mostly “ignore” each other, and as a result it has no definite size — i.e., it expands to fill a space or can be compressed, as in a tire. A liquid is a fluid where the molecules are packed together, and thus a given amount of liquid has a defined size, but the molecules are not stuck together and so it does not have an inherent shape.

Liquids contribute some gas molecules to the air (evaporation). So there is some water vapor in the air, as well as some gasoline vapor, some propylene glycol vapor, etc. There will be more of those vapors in the air if there is more of the liquid locally or if conditions are hotter. The air will “accept” more molecules of the liquid up to a point, but then it will saturate. (That is enough detail for present purposes. If you want more details, search the phrase “partial pressure”.) This means that e-cigarette “vapor” really does contain some vapor. But it is mostly in the liquid phase. That is, it is tiny little droplets of the liquid, suspended in the air. “Suspended” means that they are not in the gas phase, and thus part of the air, but are physically mixed with the air. That is the difference between dirt in water (little bits that are suspended) and salt dissolved in water (where it becomes part of the liquid). That suspension in air is called an aerosol, not a vapor.

At this point, we still have some complications. Many definitions of “aerosol” include solid particles suspended in the air, not just liquid droplets. That is, smoke would also be called an aerosol (it contains both liquid and solid bits suspended in the air). Thus, if we want to be very clear about what e-cigarettes produce, we should call it a liquid aerosol. There are a few detectable solid particles (some flavoring agents are suspended solids in the liquid rather than dissolved in it; minuscule quantities of solid contaminants come off of the hardware), but very few — not enough to invalidate this characterization.

Additionally, most definitions of aerosol include some requirement that it is in a fairly stable state. Foggy weather consists of an aerosol of liquid water droplets in the air in a stable state, so the cloud persists for a long time. By contrast, e-cigarette aerosol usually contains many droplets that are large enough that gravity will pull them out of the cloud (down to the bottom of your lung or the floor) over a relatively short period. Also, under normal circumstances (e.g., pretty much anywhere other than a vape meet), the amount of the chemicals in gas phase in the air is low enough that the droplets will quickly evaporate. These are why the visible cloud of e-cigarette exhalate normally disappears quickly. Thus, e-cigarette “vapor” is arguably not really stable enough to technically qualify as an aerosol.

That said, when scientists study something like e-cigarette “vapor”, they call it an aerosol even when it is not so stable under present conditions. So by that practical definition, it is an aerosol.

What it definitely is not is “particulate matter”. Again, we run into the difficulty of imprecise definitions. The common-language definition and everyday scientific definition (setting aside particle physics) of the word “particle” are “a very tiny solid object”. But in some contexts, it is locally defined as “anything suspended as an aerosol” which, given the option of defining aerosol to include suspensions of solids rather than just liquid, means that droplets get called particles. (This usage seems to be concentrated among people who do lab work using machines that cannot distinguish between particles and droplets that are suspended in the air, for obvious reasons.) But calling liquid droplets “particles” is grossly misleading in the context of health science. It is like referring to table salt as “metallic poison” or to acetaminophen as a “mind altering substance”, either of which may be technically true depending on your definitions, but wildly misleading except in very odd contexts.

Breathing tiny solid objects can be unhealthy, even if they are fairly inert (obviously it can be a lot worse still if they are also chemically toxic). Concern focuses on the really small ones, typically discussed under the rubric “PM2.5” (particulates in the air that are smaller than 2.5 microns across), which are produced by combustion. There is actually extensive disagreement on just how harmful such exposure is, and there is the same “public health” ideological bias in that area as there is in discussions of tobacco, declaring the worst-case estimates to be settled science when clearly they are not. (I touch on this and other details in previous posts on this topic.) But magnitude of the risk aside, inhaling the wrong particles is not good for you. Smoke is unhealthy not just because of the chemically harmful molecules in it (though that is most of it), but also because of particles themselves. Rock dusts (silica, asbestos) are harmful to breathe because of the effects of the physical particles themselves rather than their chemistry.

Breathing droplets is not at all similar to this. Particles are solids, retaining their shape and size, and thus the particle itself can cause damage. Droplets are liquids, which do not maintain their shape and size. Whether a given volume of liquid enters the mouth and lungs in the form of big droplets or small makes no difference in terms of any harms it might cause. When the droplets land, they are just a layer of liquid that does not in any way “remember” the droplet size distribution it once had.

This is not a difficult concept, though it seems to elude the ANTZ. Throw a bunch of broken glass on the ground and you have a hazard, but the same number of SiO2 molecules in the form of sand poses no risk. Size and shape matter. But whether you spray a fine mist of a liquid on the ground or pour the same number of molecules from a bucket, the result is the same. The original size and shape do not matter. The presence of the liquid might still be a health hazard, of course (if it is propylene glycol, no problem; if it is gasoline, that could be a problem). But if there is a hazard, it is completely unaffected by the size of the particles that created the puddle.

For exactly the same reason, the health impacts on the body of e-cigarette vapor are not affected by the size of the droplets in which it arrives. Smaller droplets are different only in that they find their way to more of the lung surface, and thus form a thinner layer of liquid that is absorbed faster (think about spraying a liquid across a wide area of dry ground, rather than creating a small puddle by pouring a bucket) — this is normally considered to be a feature, not a bug. In theory it could be that a liquid is more harmful to deep lung tissue than it is to other airway tissue, and thus smaller droplets (which reach the deep lungs) could have different effects. This is something that appears to be true for tiny (solid) particles. But there is simply no reason to believe this is the case for e-cigarette liquid deposition, and those who suggest otherwise are just engaged in the typical “public health” game of presenting an unsupported and wildly unlikely hypothesis as if it were a genuine reason for concern (see also: gateway).

That is pretty much what you need to know. Reading 1600 words has made you more expert on the topic than most of the faux-experts who are out there talking about this matter(!).

33 responses to “Science Lesson: what are vapor, aerosol, particles, liquids, and such?

  1. EPA & FDA: Vapor Harmless to Children

    April 3, 2014 matt black

    In the continued war on e-cigarettes, we hear about the “potential dangers” of e-cigarette vapor and the “unknown public health risks.”

    First, I find it absolutely absurd that we’re attempting to pass laws based on unknowns, but what makes it even more absurd is the fact that there’s very little that isn’t known about e-cigarette vapor at this point. The primary ingredient of concern to those who wish to see e-cigarettes banned is the propylene glycol vapor, which has been studied for over 70 years.

    I recently came across a document titled, “Reregistration Eligibility Decision For Propylene Glycol and Dipropylene Glycol“, which was created by the United State Environmental Protection Agency (EPA).

    Catchy title. I was intrigued.

    This quote caught my eye:

    Propylene glycol and dipropylene glycol were first registered in 1950 and 1959, respectively, by the FDA for use in hospitals as air disinfectants. (page 4, paragraph 1).

    In a previous post, I had shared the summary of research that had been done in 1942 by Dr. Robertson regarding the antibacterial properties of vaporized propylene glycol, but I had never heard that the FDA wound up approving it for the purpose of an air disinfectant in hospitals.

    Indoor Non-Food: Propylene glycol is used on the following use sites: air treatment (eating establishments, hospital, commercial, institutional, household, bathroom, transportational facilities); medical premises and equipment, commercial, institutional and industrial premises and equipment; (page 6, paragraph 2)


    Method and Rates of Application


    Air Sanitizer

    Read the directions included with the automatic dispenser for proper installation of unit and refill. Remove cap from aerosol can and place in a sequential aerosol dispenser which automatically releases a metered amount every 15 minutes. One unit should treat 6000 ft of closed air space… For regular, non-metered applications, spray room until a light fog forms. To sanitize the air, spray 6 to 8 seconds in an average size room (10’x10′). (page 6, paragraph 6)

    A common argument used to support the public usage ban is that, “Minnesotans have become accustomed to the standard of clean indoor air.” However, according to the EPA and FDA, so long as there’s a “light fog” of propylene glycol vapor in the air, the air is actually more clean than the standard that Minnesotans have become accustomed to.

    General Toxicity Observations

    Upon reviewing the available toxicity information, the Agency has concluded that there are no endpoints of concern for oral, dermal, or inhalation exposure to propylene glycol and dipropylene glycol. This conclusion is based on the results of toxicity testing of propylene glycol and dipropylene glycol in which dose levels near or above testing limits (as established in the OPPTS 870 series harmonized test guidelines) were employed in experimental animal studies and no significant toxicity observed.

    Carcinogenicity Classification

    A review of the available data has shown propylene glycol and dipropylene glycol to be negative for carcinogenicity in studies conducted up to the testing limit doses established by the Agency; therefore, no further carcinogenic analysis is required. (page 10, paragraphs 1 & 2)

    Ready for the bombshell? I probably should have put this at the top, as it could have made this post a lot shorter, but I figured the information above was important, too…

    2. FQPA Safety Factor

    The FQPA Safety Factor (as required by the Food Quality Protection Act of 1996) is intended to provide an additional 10-fold safety factor (10X), to protect for special sensitivity in infants and children to specific pesticide residues in food, drinking water, or residential exposures, or to compensate for an incomplete database. The FQPA Safety Factor has been removed (i.e., reduced to 1X) for propylene glycol and dipropylene glycol because there is no pre- or post-natal evidence for increased susceptibility following exposure. Further, the Agency has concluded that there are no endpoints of concern for oral, dermal, or inhalation exposure to propylene glycol and dipropylene glycol based on the low toxicity observed in studies conducted near or above testing limit doses as established in the OPPTS 870 series harmonized test guidelines. Therefore, quantitative risk assessment was not conducted for propylene glycol and dipropylene glycol.

    In a paper published in the American Journal of Public Health by Dr. Robertson in April of 1946, Robertson cites a study published in the Edinburgh Medical Journal, which was conducted in 1944:

    The report of the 3 years’ study of the clinical application of the disinfection of air by glycol vapors in a children’s convalescent home showed a marked reduction in the number of acute respiratory infections occurring in the wards treated with both propylene and triethylene glycols. Whereas in the control wards, 132 infections occured during the course of three winters, there were only 13 such instances in the glycol wards during the same period. The fact that children were, for the most part, chronically confined to bed presented an unusually favorable condition for the prophylactic action of the glycol vapor.

    An investigation of the effect of triethylene glycol vapor on the respiratory disease incidence in military barracks brought out the fact that, while for the first 3 weeks after new personnel entered the glycolized area the disease rate remained the same as in the control barracks, the second 3 week period showed a 65 percent reduction in acute respiratory infections in the glycol treated barracks. Similar effects were observed in respect to airborne hemolytic streptococci and throat carriers of this microorganism.

    I don’t expect the prohibitionist lawmakers to delve this deeply into this subject on their own, but I certainly hope that when presented with this data that they reevaluate their stance on the subject and consider what science has to say. If they don’t, they’re simply basing their judgement off of rhetoric, misinformation, and personal bias and we all know where that gets us.

    • John, thanks for all that information on the disinfecting aspects etc of PG vapor. Very good to have.

      Also, you say “I don’t expect the prohibitionist lawmakers to delve this deeply into this subject on their own, but I certainly hope that when presented with this data that they reevaluate their stance on the subject and consider what science has to say.”

      Don’t ever waste time arguing with the Antis in an attempt to change their minds. Always remember, in terms of your time and energy, that you are actually seeking to convince those who are watching the discussion, who may be leaning somewhat toward the Antis, but who actually haven’t made up their minds. The true Antis for vapers are basically the same as some of the categories of true Antis for smokers. You may not see the “Bereaved” and the “Ex-Vapers” in there, but the rest of the crew is pretty much the same and you’re not going to change them with arguments: the Neurotics, Idealists, Greedy, Controllers, et al don’t really care about our arguments — either regarding smoking or vaping — but there ARE a great number of “passers-by” in any discussion who DO care: it’s THEM that we always need to keep in mind.

      – MJM

  2. graham Entwistle

    Thank you for this.

    Why is such a concept so obvious to a layman fridge engineer like myself but so difficult for supposed “health experts” to grasp?

    Ho hum.

    I guess there’s just some deeper meaning i and millions of other vapers fail to grasp, what with being addicts and all…..

    Either that or they’re just shitting us like usual.

    • Carl V Phillips

      You ask a valid question. Several factors contribute, I think. First is that many of them are just lying, as you note. Second, “public health” attracts a lot of highly incompetent people who could never make it as refrigerator engineers. Third, there are no mechanisms in the system to correct errors. When someone in “public health” writes something wrong or does junk science, they are not criticized for it (from within “public health”). Thus, they never learn. If you engineer something incorrectly, it fails and you get the message. There is no such feedback in “public health”. Moreover, once they figure that out (or maybe they chose the field because they already knew it) it becomes clear that saying/writing things that are wrong is just as good for their measured productivity as things that are right, so out of dishonesty or just laziness they just churn out the falsehoods.

  3. Hi Carl.
    When I said yesterday: “…..and whatever pm 2.5 particulates happen to be contained within the water vapour.” I did not make myself clear. What I meant was that the ‘aerosol droplets’ (fog, if you like) might well well have within them tiny particles (like diesel fumes). I was thinking about how rain carries dust within the drops.

    • Carl V Phillips

      Ok, I see. That is the same as I was talking about when I mentioned the tiny bits of suspended solid in “vapor”. But fog vapor will only have PM2.5 in it if there is PM2.5 already around in the air. It cannot create any. Indeed, it will clean a lot of them out because a lot of the droplets do settle to the ground even when it is mostly stable.

  4. “There is actually extensive disagreement on just how harmful such exposure is, and there is the same “public health” ideological bias in that area as there is in discussions of tobacco, declaring the worst-case estimates to be settled science when clearly they are not.”

    Twenty or thirty years ago it seemed that Public Health’s attention was largely focused on the larger PM 10 particles. I believe that even EPA/OSHA type concerns focused mainly on their measurement.

    My sense at the time when the switch to PM 2.5 came about was that a good part of the motivation behind the switch came from the fact that PM 2.5 seemed to be far more unique to tobacco smoke — thus making it a far more potent weapon in characterizing secondary tobacco smoke as a risk.

    We often see statements like “PM 2.5 levels were 75% (or 750%) higher in a building (or a bar) where smoking was permitted than in one where it was banned.” Given that PM 2.5 particles ARE in essence “smoke” (I believe I am fundamentally correct in saying that, no?) then such statements are simply redundant: they’re saying “There’s more smoke in the air in a room/building where people are smoking than there is in one where people are not.”

    The big problem arises when they take the measurement of such smoke as necessarily causing the same harm as the measurement of PM 2.5 produced by diesel engines, industrial processes, and commercial incineration. I like to characterize it as being similar to saying, “This teaspoon is full of sugar crystals. This other teaspoon is full of arsenic crystals. The crystals are the same size (and maybe of the same color?), so therefore they are equally dangerous. So, I will swallow the teaspoon of sugar and you will swallow the teaspoon of arsenic and we’ll both experience the same effect!”

    Hmmm… Think Stanton Glantz of James Repace would be willing to take me up on that offer?

    MJM, adding some powdered sugar to the top of a donut and offering it around…. any takers?

    • Carl V Phillips

      I think that claim is rather tenuous. First, it appears (at my level of expertise, which is decent but not that of a specialist in the area) that the change from PM10 to PM2.5 was based on good evidence that the portion of PM10 that really was causing the problem was at the PM2.5 end. The change also came with better detection methods that could distinguish between them. Second, to the extent that there is an ideological bias driving anti-PM crusades, it is anti-car and anti-coal (which is pathetic — the real health case against coal is the mercury emissions).

      The anti-smoking activists glommed onto the claims, it is true. But it is not like cigarettes do not produce PM10 also (which is a superset of PM2.5, of course). But the PM people are actually quite a bit smarter than the anti-tobacco people, and the latter just stumbled along with it, not really even understanding it.

  5. Carl, as usual you’ve made this problem very accessible for the lay reader. I’ve struggled with the concepts and how to explain them to lay persons for several months now (since I became aware of how much tripe our dear Prof. Glanz has been putting forth). Using the spray vs. bucket analogy is perfect for the purpose. Pity I didn’t see the simplicity myself.
    Now there’s another issue that adds on to this. The concept of suspension and settling. When aerosols are fine enough they float along in the air and do not settle, especially in the presence of turbulence (such as is encountered in the bronchial tree) thus only a small percentage relative to the size and density of droplets will actually settle out into the lung while the rest is exhaled. Likewise for the third hand exposure issue, the smaller aerosol particles will disperse further before settling further diluting the deposition (by increasing the area).
    Thanks for taking the time to create this.

    • Carl V Phillips

      That is one real effect of droplet (or particle) size that I did not mention, yes. Since I am in the business of illustrative analogies, it is similar to when you are driving and there is a critter in your path. If it is a mosquito, it is very unlikely you will hit it because it will be pulled in the slipstream of air around your car. I has so little inertia (mass) that it moves with the air as if it were part of it. Similarly, a small enough droplet will flow with the air that surrounds it and its momentum is unlikely (within a few seconds) to carry it to the side of your lung. If the animal in question is a grasshopper, then there is a good chance you will hit it, though there is a chance it will flow with the air. Compare: a larger droplet, once it is moving in a particular direction, is fairly likely to keep going until it hits something, but might not. If it is a moose, well….

      So that “feature not bug” point I made has its limits. If too much of the mass is in the form of too small droplets, they will not be efficiently deposited.

      In terms of environmental deposition, though, I am not sure how much this matters. Evaporation should be rapid enough, under normal circumstances, that beyond the immediate area where lots of larger droplets fall out, it mostly should be gas phase. Within the lungs there will be some evaporation, but there is not much time and the partial pressure will be higher because there is so much liquid in a small space.

  6. Pingback: Science Lesson: what are vapor, aerosol, particles, liquids, and such?

  7. Carl,

    Where does vaping actual tobacco leaf fall into all of this?


    • Carl V Phillips

      It depends — mostly on the peak temperature, though somewhat on the formulation and some other variables. Somewhere I have some detailed notes on this (I can try to find them if you really want). Working from memory: If it is hot enough then you start tending toward the effects of burning (which liberates some solid bits), even if the leaf itself is not sustaining smoldering or burning. The earliest cigarette-like products and hookahs seem to be in this range. So hot enough and there will be some particles produced, though not nearly as many as with smoke. Those products do produce quite a bit of CO, which means that hydrocarbons are breaking down which probably (not necessarily) is a marker for throwing out particles.

      Control the heating better, as in the modern HnB products, and you should only get outgassing of volatiles which are then either inhaled as gasses or condense into droplets (after being heated enough to become gasses and leave the solid matrix, but then cooling in the air while being inhaled). There is also a step in controlling the heat even better, where you make sure you only get volatilization and are not producing pyrolysis products (which are also gasses or liquids at room temperature).

      • Thanks Carl. I should have mentioned that I was referring to modern HnB/vapor products that create zero combustion and do not use carbon as a heating source. I would love to hear more about what notes you have stashed away on this subject.

        “There is also a step in controlling the heat even better..”

        Are you referring to convection, as opposed to conduction heating?

        For whatever it’s worth, since I started vaping (pipe) tobacco I no longer inhale. Maybe this is also a valid route to THR. I would tend to think that it is.

        It sure would be nice to have a snus-inspired HnB pipe gizmo in the future:-)

        • Carl V Phillips

          There are various ways to avoid getting too-hot spots. Convection is certainly one of them.

          Mouth puffing is definitely risk reducing for combustion gas. It is probably also so for vaping. That option is one of the many reasons that all of those overly-precise numbers about risks — reported as if they were physical constants — are absurd. It is presumably also why cigar and pipe smoking is much lower risk than cigarette smoking — it is not the devices, it is the most common way of using them.

    Line breaks: va¦pour
    Pronunciation: /ˈveɪpə/
    (US vapor)
    Definition of vapour in English:

    1 [MASS NOUN] A substance diffused or suspended in the air, especially one normally liquid or solid:
    dense clouds of smoke and toxic vapour
    [COUNT NOUN]: petrol vapours

    • Carl V Phillips

      That is a rather odd definition. It is flatly contrary to the accepted definition in scientific contexts. Presumably the list continues with other interpretations of the word, including the scientific one and (if it is up to date) some version of “the stuff that comes out of e-cigarettes”.

      • Thank you. Indeed, Oxford continues, “[Physics] A gaseous substance that is below its critical temperature, and can therefore be liquefied by pressure alone.” Also, its definition of “vape” is: “inhale and exhale the *vapour* produced by an electronic cigarette or similar device.”

        My point is, however, that vapor is a perfectly appropriate term for EC aerosol. If scientific terminology uses a term in one way, then it doesn’t make the more widespread connotation inaccurate or unscientific.

        Furthermore, vapor meant steam before the scientific definition of vapor existed.

        Wikipedia’s lead paragraph on e-cigs says, “They do not produce cigarette smoke but rather an aerosol, which is frequently but inaccurately referred to as vapor.” I tried changing this statement based on Oxford, but it was rejected because it is backed a peer-reviewed medical article (and that trumps Oxford’s understanding of English).

        I feel that defending the term usage of vapor with regard to e-cigs is important, as it makes people intuitively feel that this is a product which is significantly safer (which happens to concord with the science).

        • Carl V Phillips

          Well, that is what my second paragraph says. (Minus the bit about “safer”. Not calling it “smoke” is a good idea for that, but if it had gotten labeled “ruyite” and “ruying” that would serve that purpose also. Keep in mind that many of the connotations of “vapor”, particularly historically, are negative also.)

          Wikipedia is a disaster for dealing with controversial subjects. It is great for looking up a lot of things — simple factoids, settled science, formulas — but it is the equivalent of reading the newspaper when something is politically in play.

  9. Do you know any study having analysed the exhaled vapour droplets? Any idea of its water content? Thks

    • Carl V Phillips

      Air in the lungs rapidly saturates with H20(gas) (i.e., has 100% relative humidity at body temperature), ecig liquid is hydroscopic, and the droplets provide a nucleus for condensation of the H20 vapor. The result is that there is a lot of water in ecig exhalate, and a lot of it is in the droplet phase. But that is pretty difficult to measure (tiny bits of liquid water have an annoying habit of evaporating before you can weigh them) and it will vary hugely.

  10. Would it be true to say that in any situation where the humidity is above zero that there is “water vapor” in the air?

    I’m thinking that the real distinction in terms of how vapor is commonly used in the language simply refers to visible vapor. And I’m further thinking that visible vapor may only occur at a certain level of condensation into substantive droplets of a certain size and/or concentration. Are my thinkings well thought? Or just vaporous?

    – MJM

    • Carl V Phillips

      “Humidity is above zero” (either relative humidity or absolute) is definitionally equivalent to “there is water vapor in the air”.

      Actual vapor is generally not visible. Having a lot of some gasses — some of which are vapor, i.e., “normally” a liquid — in the air makes it hazy. But the distinctly visible bits will be aerosol droplets or particles.

      • “Actual vapor is generally not visible… the distinctly visible bits will be aerosol droplets or particles.”

        So Vapers would more accurately be described as Dropplers? :>

        • (You’ll never see this coming) I guess when they dropple, they experience the Droppler effect? *derp* :D

  11. Or, to take a Disneyfied approach… Dropleteers!

  12. Pingback: FDA | warrior3995

  13. Pingback: California ecig “regulation” hearing: a catalog of lies (part 1) | Anti-THR Lies and related topics

  14. Well, the difference is just a letter. W is sometimes right? :)
    Wikipedia: The similar-sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is an optical device used for making observations deep under water.

    • Wikipedia is usually right because it is mostly about uncontroversial factoids. Their process is also good for fixing errors that even those erring say “whoops, you are right” when it is pointed out (like commonly confused words). But it fails miserably in cases where there is deep genuine controversy or where people who know something about the topic insist that they know more than they really do. E.g., that process cannot be trusted for anything in science that is not either (a) so technical that only serious experts have opinions or (b) so settled that it has been taught correctly in grade-school for decades.

  15. Pingback: Serious ethical concerns about public health research conduct; the case of vape convention air quality measurement | Anti-THR Lies and related topics

  16. [Quote] Breathing droplets is not at all similar to this. Particles are solids, retaining their shape and size, and thus the particle itself can cause damage. Droplets are liquids, which do not maintain their shape and size. Whether a given volume of liquid enters the mouth and lungs in the form of big droplets or small makes no difference in terms of any harms it might cause. When the droplets land, they are just a layer of liquid that does not in any way “remember” the droplet size distribution it once had.” [End Quote]

    This is not a difficult concept, the writer continues. However, does it mean to the writer that PM2,5 in the form of droplets, considering the droplets are non toxic in nature, does not or rather can not harm the respiratory system or cardiovascular system. How about any droplet that formed around a piece of particulate matter? Say PM0.1 floats and are the starting ground for PM1 droplets.

    Is there a citation in a peer reviewed or published article you can point me to? I was looking and came to this forum.

    Kind regards.

    • Carl V Phillips

      Um, well, the citation for what you quoted from this published article is this published article. This blog is more credible than any peer-reviewed journal in this space, but that should not be a problem.

      Your second paragraph is a bit confusing to me. I did not assert that particular droplets ARE not chemical toxicants, just that IF they were not, then size does not matter. In another post on this topic (which is more complete than this one — I have written more about this) I note that larger droplets may be worse if there is a chemical hazard, because they concentrate it more. If there were a potentially physically harmful particle within a droplet, which is a thing that happens, then it might still lodge somewhere it is harmful and when the liquid is absorbed, it is still there. However, it is often the case that the droplet is large enough that it causes the particle to be deposited somewhere harmless, like the back of the throat because it has too much momentum to make the turn.

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