A full guide to vape aerosols: Post 10, environmental aerosols (part 3, the "particles")

This is the tenth Substack post. It is the third one of a series of 3 posts dealing with environmental vape aerosols. A 4th post reviewing the literature is forecoming.

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This 10th Substack post expands the previous 8th and 9th posts by clearing the confusion around the “particulates” of exhaled vape aerosol. Most of the literature published by tobacco control, public health and regulatory institutions reports that bystanders face concerning health risks from their exposure to the ultra-fine “particulates” (UFPs) of exhaled vapes, as these UFPs deposit deeply in their lungs. This claim is based on a factually false identification of the UFPs of vape aerosols with the UFPs of air pollution and combustible sources.

Take home message: The claim that bystanders face serious health risks from deeply inhaling tiny ultra-fine “particulates” (UFPs) of exhaled vapes is factually false, as it is based on a mistaken identification of these UFPs with UFPs of air pollution or combustion produced smokes.

Summary of previous posts:

Post 1. Basics: what is an aerosol? Vapes and kettles. Byproducts of the heating process. Post 2. Physical processes in vaping. Essentials of laboratory testing. Optimal Regime. Post 3. Overheating: exponential production of toxic byproducts and the “dry puff”. Post 4. Laboratory testing. The CORESTA standard and the evolution of the vape market. Post 5 Metals. Post 6: Organic byproducts. Post 7: vape exposure in preclinic studies. Post 8, basics of environmental vape aerosols. Post 9, chemistry of exhaled vapes and exposure biomarkers.

Environmental vape aerosols.
Post 10: Part III, the “particles”

NOTE ON NOMENCLATURE. I will not use the adjective “second hand” to denote aerosols that originate from users’ exhalations (ie “second hand smoke” or “second hand aerosol”). Instead, I will refer to them as environmental tobacco smoke (ETS) and exhaled vape aerosol (EVA)

Quick summary of Post 9

Different types of studies (1) cross sectional based on self-reported questionnaires on health effects from exposure to environmental vapes, (2) controlled chamber studies that almost always consider unrealistic exposures and (3) the study of “vaping atmospheres” in non-smoking environments. Evidently, (3) provide the best quality evidence of exposure risks.

I reviewed and analyzed two key studies:

Chemistry . A study conducted in a large closed indoor space where 5 regular vapers vaped 12 hours ad libidum some days and abstained other days. Chemical composition of the environment air in vaping and no-vaping days was compared. Results: vaping and non-vaping atmospheres were almost indistinguishable, the only chemical signature left by vaping was: in the particulate phase a residual concentration of glycerol and nicotine, while in the gas phase a very slight increase of formaldehyde, which still remained well below standard air quality limits and most smoke free spaces.

Biomarkers. Another study lasting several weeks compared 29 non-smoking “vaping homes” (a resident vaper and an exposed non-user) with 21 homes where no one vaped or smoked (the control). Vaping was ad libidum in vapers’ own devices. Saliva and urine biomarkers of cotinine, glycerol, propylene glycol, nitrosamines and other organic compounds were collected from all participants. The authors were unable to distinguish the vaping and non-vaping homes from purely environmental measurements (particulate numbers were the same). The only trace of vaping in biomarkers of those passively exposed compared to controls were: a very slight cotinine increase, at levels within the range of non-smokers and a higher (but still minute) presence of glycerol and propylene glycol.

Conclusion. It is very difficult to distinguish in smoke-free environments an exposure to contaminants between a vaping and non-vaping atmosphere (under normal conditions). Typically, the only noticeable trace of environmental vape aerosols are residual concentrations of propylene glycol, glycerol and slight increase of cotinine in biomarkers of passively exposed bystanders.

Motivation for Post 10.

The effects of bystander exposure to exhaled vape aerosols is a very important issue, either in drafting public policies and/or in the acceptance and advancement of Tobacco Harm Reduction. Given its visual similarity with smoking and the common content of nicotine, there is a powerful inertia among tobacco controllers, regulators, health professionals (and even the general public) to automatically extend to vaping usage in public spaces the same regulations that apply to smoking. Is this justified?

It is not justified, this visual similarity hides the fact that the physical and chemical nature of environmental vape emissions (which I discussed extensively in Post 8 and Post 9) imply an exposure that is short timed, spatially limited, intermittent and overwhelmingly less hazardous than the hazardous long time exposure to environmental tobacco smoke (ETS). Since public policies must be “evidence based”, it is important to examine the arguments of the scientific literature that claims to provide this evidence.

The majority of studies of the “independent” literature (not funded by industry) claim that environmental vape aerosols “impair” indoor air quality and pose concerning risks to exposed bystanders. The two studies I reviewed in Post 9 clearly show that there is no such impairment of indoor air quality.

The main argument behind assessment of concerning risks comes from the fact that vaping generates ultra-fine particulates (UFPs) which are deeply inhaled by passively exposed bystanders. The literature emphasizes risks for children and vulnerable individuals. In the present post I provide a discussion of the arguments around UFPs in exhaled vapes.

Misrepresentation of the vape “particulates”

There is an extensive literature of publicly funded studies (from universities, public health and regulatory agencies, the WHO, etc) on exhaled vape aerosol (identified as “second hand aerosol”). The vast majority of these studies concludes that bystanders exposed to exhaled aerosol face concerning health risks because its particulate phase is dominated by UFPs that can be deeply inhaled into the lungs. Evidently, authors making this argument hint or suggest (some like the WHO even openly declare) an equivalence of exhaled vape UFPs with UFPs of air pollution or tobacco smoke, for which this exposure risks have been well studied and established (see the latest WHO air quality guideline).

However, practically none of these studies on environmental vape aerosols has conducted or presented or cited any actual experiment or empiric proof that would support an equivalence of UFPs of exhaled vapes and UFPs of air pollution or combustion sources, as such evidence would clearly provide solid support for their claims on exhaled vape risks from UFPs.

Practically all these studies circumvent and remain aloof on this important lack of empiric support for an important argument that would justifies their stance on the risk profile of environmental vape aerosols. These articles find particle numbers or mass densities distributions, some present simplified lung deposition models, very few provide a substantial chemical analysis. Some studies even recognize basic known physical and chemical properties of vape aerosol droplets (as I have described in Post 1, Post 2 and Post 3), but do not realize that these same properties that they recognize would seriously question their harsh risk assessment on exhaled vape particulates.

These are some of the arguments used on the “particulates” of exhaled vapes contrasted with the evidence

• Huge numbers of “particles”. Chamber studies report (occasionally with alarm) that puffing a vape rises particle numbers in the user’s personal space by 4 orders of magnitude above the environment level of normal airborne indoor pollution (the same happens when lighting a cigarette with a 6 order of magnitude rise). This rise of particle numbers is not an abnormal phenomenon, particle number densities of non-biological indoor anthropogenic aerosols occupying relatively small volumes are enormous: from 10 to over 1000 million of particles per cubic centimeter. In particular, particle numbers per cubic cm of tobacco smoke are 10-100 times larger than in vape aerosols (inhaled or exhaled).
  
  However, a density comparison with the normal indoor environment is misleading, since vape particles (droplets) occupy a small volume (< 1 cubic meter) and rapidly evaporate and disperse, while the indoor environment is typically over 100 cubic meters (4 orders of magnitude larger), so it includes much more particles that (mostly) do not evaporate but deposit in walls and surfaces. Large particle numbers in a personal space are not in themselves hazardous, it depends on the nature of the particles: the sauna cloud is an aerosol containing as much particles (water droplets) as an exhaled tobacco smoke puff, this does not mean both are equivalent to assess hazards or that we should worry because their particle numbers density is comparable.

  

  Figure 1. Same particle number density does not imply same risk to bystanders

• Very small “particles” deposit deeply in the lungs. Sizes of particulate matter “PM” (particles in aerosols) are classified as PM10, PM2.5, PM1 (all particulates below 10, 2.5 and 1 micrometers), while “ultra-fine particles” (UFPs) are much smaller (below 0.3 micrometers). As a reference, human hair thickness is between 50-70 micrometers, a very large molecule is 0.001 micrometers
  

  

  Figure 2. Relative sizes of PM, human hair and fine beach sand. Source

  In most aerosols there are much more smaller (< PM2.5) than larger (> PM10) particles, but the latter concentrates most particulate mass. In tobacco smoke and in vape aerosols average particle sizes are in the same UFPs range. The main argument to justify concerning inhalation risks from air pollution and tobacco smoke follows from lung deposition models showing that minute UFPs and PM2.5 tend to deposit deeply in the alveoli when breathed.

  

  Figure 3. Relation between PM size and depth of lung deposition. Source

  Many studies published by public health institutions on exhaled vape aerosols automatically translate risks from UFPs and PM2.5 of air pollution to UFPs and PM2.5 of environmental vapes, citing also lung deposition models. However, the models used in the studies on environmental vape aerosols are too simplified to predict actual lung deposition of either inhaled or exhaled aerosol. I discussed this issue in Post 8 and will comment further ahead in this post.
  
  It is also important to stress that UFPs are not automatically dangerous just because they are tiny small and can be deeply inhaled. This study (Ogulei et al) sampled particulate matter of several common household aerosols: boiled water in a kettle, frying tortillas and a burner, finding their particulate phase overwhelmingly in the UFP range. In fact, diameters of water vapor particulates (water droplets) were on average 0.01 micrometers.

• Comparing apples with oranges. A full knowledge of the lung deposition pattern of PM2.5 and UFPs in a given aerosol is insufficient to assess its inhalation risks, since particles of the same size can have very different physical properties and chemical composition, and thus pose different levels of toxicity and risk (as in the examples examined by Ogulei et al mentioned above). Water vapor in a sauna or a shower contains as many PM2.5 and UFPs (water droplets) as PM2.5 and UFPs of air pollution or tobacco smoke. In all these aerosols (sauna, air pollution, tobacco smoke) the deposition models predict deep inhalation into the lungs. Does its same lung deposition of UFPs makes water steam as hazardous as air pollution or tobacco smoke? Obviously not.

• PM2.5 and UFPs of air pollution and tobacco smoke. Their chemical composition is multi-factorial, depending on their source, its formation process and its evolution. Primary UFPs originate from combustion sources and have a large carbonaceous content (including soot), the secondary UFPs include nitrates, sulphates, ammonia from interaction with atmospheric gases and photochemical reactions. Outdoor UFPs penetrate indoors and also form from combustion sources, mostly and specially from cooking, but also from heating with coal, wood or dung, lighting incense and candles (and of course from smoking). These reviews (here, here and here) provide an accessible description of their properties.
  

  There is evidence that UFPs from air pollution in indoor spaces are hazardous (see here and here), they are linked to biomarkers of oxidative stress (see the latest WHO air quality guideline for a review of epidemiological studies). UFPs are specially worrying due to their small size and deep lung deposition, but also (and mostly) because a large share of their chemical composition is made of toxic or carcinogenic compounds: carbonaceous molecules (including polycyclic aromatic hydrocarbons), nitrates and sulphates, plus inorganic compounds. The carbonaceous compounds are semi-volatile and non-volatile, so they do not evaporate and remain airborne for long times. Since they are insoluble in water, once inhaled there is an enormous potential for lung damage.

• PM2.5 and UFPs of environmental vapes. Save for the same small diameters and large numbers, their physical and chemical properties clearly and indisputably prove that vape particulates (droplets) bear no relation with those of tobacco smoke and air pollution. They are liquid droplets made almost 100% of PG, VG, nicotine and water. Since PG and nicotine are highly volatile, when the droplets are exhaled into air that is much colder and drier than air in respiratory tracts, they rapidly evaporate into the diluting and dispersing gas phase, with the already tiny droplet diameters decreasing further until their full dilution in environmental air. Since all vape aerosol released into the environment only comes from the vaper’s exhalation, the exposure to the particulates (droplets) is short timed and intermittent (1-3 minutes per puff) and bounded to the volume close to the personal space of the vaper.

Discussion

The claim that exposure to UFPs of exhaled vapes poses serious risks to bystanders is an old contention that dates back to 2014 or earlier in the blog of Prof. Stanton Glantz from the UCSF (the link to his blog on this entry no longer works). It appeared also in a chamber study in 2014 by Schober et al. This contention was first criticized by Carl Philips in his blog (here and here) and in the blog of Clive Bates in 2014 and 2016 (here and here, see item 5). Curiously, neither Glantz nor Schober et al explicitly and openly make the parallel to UFPs of air pollution, they just “hint” it by concluding harms from exhaled vapes. It is puzzling to read after 11 years that the same “hinting” of a factually mistaken claim is still voiced by so many studies funded by public institutions out of tax payers money.

There is solid empiric evidence (see Gregory et al and Li et al) that the particulate phase of inhaled and exhaled vape aerosols consists of liquid droplets whose chemical composition is similar to that of the e-liquid and is about 97-98% made of glycerol (VG), propylene glycol (PG), nicotine and water. This fact emerges from the physical processes forming the aerosol (see Post 2), which mostly involve a heat exchange cycle, phase changes (evaporation, condensation) and low energetic chemical reactions forming byproducts at trace levels. As long a vapes are operated or tested under normal optimal conditions (see Post 3 and Post 4) all other compounds (specially aldehydes) appear at trace levels as byproducts of heat degradation (low energy pyrolytic) reactions from PG, VG and flavorings.

However, the heat degradation reactions taking place when the e-liquid is heated do not occur once the aerosol is inhaled under the conditions inside respiratory tracts (37 °C and ~100 relative humidity). Since most inhaled aerosol (including aldehydes) is retained (see Post 8), the exhaled aerosol is very diluted and is thus even “cleaner” (much less byproducts) than the inhaled one, so it is closer to the 100% composition of VG, PG, nicotine and water.

This is supported also by physical processes, since exhaled vape aerosols emerge from a hot humid environment (respiratory tracts) into a much colder and drier air, a sharp environmental transition of a gas plus droplets evolving towards thermal equilibrium with surrounding air (acting as a thermal bath). This transition strongly favors a rapid (< 2 minutes) evaporation of PG and nicotine in the droplets to a rapidly diluting and dispersing gas phase, with the remaining VG in much smaller droplets. This remaining trace of VG and nicotine was experimentally detected by van Drooge et al (see Post 9) as the only signature that remained in the environment after 12 hours of vaping.

Given the available knowledge on thermal and phase change processes in an aerosol like that of vapes, together with the experimental evidence, there is no justification for authors funded by public institutions to keep misrepresenting the particulate phase of this aerosol in chamber studies at least since 2014. Curiously, some authors know that vape droplets are chemically different from air pollution particulates (for example Schober et al), yet their conclusions on risks are inconsistent with this knowledge. Either the authors of these studies are ignorant on basic aerosol science, or are not ignorant but their conclusions are determined by their commitment to a political agenda to hype risks on environmental vape aerosols in order to influence public policy.

Finally, it is important to mention that lung deposition models used in some chamber studies, as for example the multiple-path particle dosimetry (MPPD v2.1 (Protano et al), need to consider the various aerosol phenomena taking place inside respiratory tracts to model lung deposition (see Post 8). It is specially important to consider the effects from hygroscopic droplet growth, which changes the simple deposition pattern only based on droplet size. There is also hygroscopic growth in the particulates of tobacco smoke, but deposition patterns are more complicated due to the much higher chemical complexity of liquid droplets and the fact that some particulates are solid.

Conclusions & further posts.

I hope this post has cleared the confusion around the risk from bystander exposure to Ultra Fine particulates (droplets) of environmental vape aerosols.

Conclusion on “particulates”. In terms of the physical and chemical properties of its PM2.5 and UFPs, environmental vapes are much closer to the sauna clouds or to fog than to PM2.5 and UFPs of air pollution or tobacco smoke or any combustion source. The droplets of environmental vape aerosol rapidly evaporate and disperse within a small volume around the personal space of the vaper, while PM2.5 and UFPs of indoor pollution are spread throughout the indoor volume and do not evaporate.

Since indoor spaces have a large area per volume, PMs and UFPs interact with pollutants (either gases or aerosols) in walls and surfaces. As a contrast, exhaled vape droplets disperse in a relatively small volume and only in small indoor enclosures deposit on walls. The claim that UFPs or environmental vape aerosols pose concerning risk to bystanders from an analogy with PM2.5 and UFPs of air pollution or combustion sources has no support in aerosol physics and chemistry. Even cooking aerosols have a higher toxicity content, a larger spatial spread and remains much longer time in the environment.

Comparisons beyond smoking. While ETS is an important comparative reference, smoke free spaces are increasingly becoming the norm regulating public and private indoor spaces. Therefore, part of the evidence to assess the safety of exposure to environmental vapes must be based on comparison with the many polluting aerosols still present in indoor environments that are smoke-free, whether natural (penetrating outdoor pollution) or human made (anthropogenic), cooking aerosols, odorizers, electronic appliances, paintings, cosmetics, paper walls, rugs, furniture, biological aerosols (airborne bacteria, and fungus) and even aerosol emitted by the human body. Comparison of exhaled vapes with other pollutants is an important task that I will address in future posts.

Next post. I will review the literature on exhaled vape aerosols, specially the many chamber studies, including studies of vaping inside automobile cabins, in vape shops and in vape conventions.