On the global intensification of "vapor-free" policies (Part 2)
Part II: Review of the literature on environmental vape aerosols.
Dear readers
I begin in this post the second part of my critique of “vapor-free” policies. You might want to read the first part. I start now a series of new posts presenting a rigorous critical revision of the extensive literature on the environmental emissions of vaping, the so-called “passive vaping” or “second hand” aerosols. I have presented a technical description of environmental vape aerosols in Post 8, Post 9 and Post 10.
While there is a general scientific convergence of experimental facts on environmental vapes, there are enormous difference in the interpretation of experimental results between public health (“independent”) and industry funded studies. I have found much better technical quality in industry studies, which present a neutral narrative and simply report their findings.
As a contrast, most (with some exceptions) of public health studies accompany their findings with a hostile ultra-protective narrative, forcefully recommending bans of the use of vapes in all smoke free spaces (this despite the fact that most often their own findings do not justify this recommendation).
There is no doubt that “independent” research in this topic is constrained to fit an ideological agenda: to apply to vaping the “de-normalization” applied to smoking based on harms from passive smoking.
While there was a utilitarian justification on the imposition of extensive smoke-free policies (despite the pseudo science on passive smoking I described in my previous post), the attempt to “de-normalize” vaping has zero scientific basis and becomes purely and crudely an effort to impose an ideologically motivated form of social engineering and lifestyle control.
Reading guideline for this post
I present in this post a critique of (in my view) a very emblematic “independent” study on exhaled vapes (notice it already has a Pub Peer comment)
The review is based on a Pub Peer comment I placed recently
Despite having 24 authors, it is a technically superficial mediocre study and is not well known, it has only 12 citations in Google Scholar. So, why is is emblematic?
The authors found that the aerosol generated by two vapers puffing low powered devices (Juul and Just Fog) completely disperses in 10-20 seconds at 2 meters distance, becoming practically indistinguishable from the background.
This result is consistent with results from better quality studies (see chamber studies in Post 8), showing same behavior at shorter distances. Actually, it is EXCELLENT NEWS: bystanders exposed to exhaled vapes face an extremely weak pollution level.
However, despite their own findings, the authors bend backwards trying to argue that this reduction of pollution levels “might” not be sufficient to reduce or eliminate harms to bystanders, specially children and vulnerable individuals (no toxicological reference, nothing, just a rhetorical statement). To justify this sort of “U-turn” from their own results they present various technically flawed arguments that are easy to refute.
The study I review in this post is the most obvious and blatant case, but almost all public health studies that found very weak pollution from exhaled vapes follow this “U-turn” of their own results. Practically all introduce the subject with a hostile background narrative, strongly hinting in the discussion risks of harm of bystanders.
However, since their outcomes do not look sufficiently scary, they cannot affirm, so they hint, mostly using weasel words like “might”, “could”, “potentially”, etc. Nevertheless, the recommendations are to ban “to protect” children, pregnant women and vulnerable frail individuals. My review of this study will highlight some important critical issues of public health research on environmental vape aerosols
Misrepresentation of “particles”
The authors only measured ultra-fine particles UFPs, deceitfully describing them in the title as “particulate matter” PM (the hint to air pollution). This deceitful identification of the liquid droplets (particulate phase of vape aerosols) with air pollution PM is a common feature in public health studies.
It is ironic (but illustrative) how the authors’ main experimental result (full dispersion of the aerosol in < 20 seconds) is in full contradiction with their “hinting” an equivalence of vaping particles with air pollution PM. Unfortunately, the authors misrepresented their most important finding.
Vaping in the context of indoor pollution
Some public health studies compare with “second hand” smoke, but most only focus on exhaled vapes, in isolation (as comparing with an abstract “zero pollution” fiction). This tendency to isolate vaping has recently become prevalent.
Most studies on passive vaping ignore that in indoor spaces where no one vapes or smokes all dwellers (including children and vulnerable people) are exposed to multiple prevalent sources of pollution: penetrating outdoor air, aerosols from cooking, wall cleaning, sprays, gas emissions from walls and furniture, etc).
To compare with indoor pollution, it is necessary to bear in mind that the reviewed study found a very low particle number concentration (PNC), almost indistinguishable from background levels. Yet, the authors hint risks to bystanders, emphasizing children and vulnerable individuals.
To verify if the authors’ risk warnings are sustained in published evidence, I searched data on indoor pollution from UFPs, in many private and public indoor spaces: homes, schools, offices, restaurants, even in spaces with majority children occupancy. In all spaces PNC was at least one order of magnitude (10 times) higher than what this study measured.
Particle counting is not sufficient, we need to consider the chemical nature of the particles and evaluate the inhalation dose from the exposure time. The “particles” in exhaled vapes are rapidly evaporating liquid droplets with low toxicity (PG, VG, nicotine and water), whereas particles in air pollution, cooking and washing aerosols have much more complex and toxic chemistry. Also, exposure to exhaled vapes is short and intermittent, while there is 24 h/day exposure to air pollution and up to 2-3 hours to cooking aerosols.
The only way to detect high pollution levels from environmental vapes is in extraordinary and sporadic events where many vapers vape jointly in the same space: vape shops or vape festivals. But even in these events the numbers of UPFs is below busy restaurants and heavy vehicle traffic.
Excessive and irrational precautionary approach
It is disturbing to see the excessively precautionary approach to vaping that borders in irrationality. Evidently, children and vulnerable individuals must be protected from pollution, but from all pollutants not only from passive vaping. But there is a limit on how much authorities can implement this protection, a limit that is not applied to vaping.
Heavy cooking or operating an old vacuum cleaner or lighting candles can produce intense indoor pollution, but authorities recommend kitchen ventilation and common sense: do not place your child or frail grand mother next to a hot oven while cooking, or close to the wall while washing it, or close to the exhaust of a car or a vacuum cleaner. Authorities recommend common sense precautions (including ventilation).
Yet, public health researchers and authorities do not offer such pragmatic common sense approach to deal with indoor vaping (ventilation), they only express dire scary warnings that children “might, could potentially” inhale UFPs that will go directly into their lungs, or the risk of addiction from inhaling nicotine, as if children in non-smoking environments lived in zero pollution paradises only disrupted by vaping.
This attitude assumes that vapers and vaping parents are, either irresponsible incompetent idiots or motivated by malign intent, something not assumed in people who cook or do other activities that emit aerosols.
Vaping is an activity for healthy adults
Vaping is an activity conceived exclusively for healthy adults, like drinking whisky or smoking tobacco or cannabis. Drinking whisky is illegal for minors (yet some minors illegally drink), but the safety of whisky is not evaluated by its potential effects on children or frail individuals. However, for mainstream public health (authorities and researchers) the safety of vaping is strictly evaluated by its potential effect on children, young people and frail individuals.
Evidently, vaping (and alcohol drinking, smoking, etc) must be prohibited in a nursery or any indoor space whose occupancy is made of children and vulnerable individuals. However, there are indoor spaces where adult drinkers can socialize while they enjoy their drinks (alcohol drinking is regulated, not “de-normalized”).
OK, smoking (tobacco or cannabis) is different from drinking whisky: emissions can be harmful to others, so there is justification in banning indoor usage. However, passive vaping is not passive smoking, its emissions do not carry the risks of passive smoking. Still undesired exposure should be prevented, but there is no reason why adults cannot vape and socialize in indoor spaces where exposure is voluntary.
Allowing public indoor spaces were voluntary exposure to vaping might produce complaints. True, but there are always complaints on behavior that some people find unacceptable and even potentially harmful (drunks in a bar or too loud music in a party or disco). Authorities are aware of this, so they regulate drinking and loud music, but do not panic and enact blanket prohibitions because some folks object or report discomfort. There is no rational reason to treat vaping differently.
Who are the authors?
They are 24 researchers of the TackSHS project funded by the European Union’s Horizon 2020 Research and Innovation Programme. “TackSHS aims to improve our understanding of second-hand tobacco smoke and e-cigarette emissions and find ways of tackling the health burden caused by exposure to these aerosols.”
It involves researchers from public health institutions in Spain, Greece, Italy, UK, Ireland and Belgium. Practically all their studies concern environmental vaping aerosols, not environmental tobacco smoke. Their papers involve many authors, though it is not clear which authors really conducted the research. All their studies conclude that environmental vaping “impairs” air quality. Although some of their studies recongnize the presence of other pollutants, their approach is focused on vaping as the agent disrupting an otherwise unpolluted paradise. Most of their studies are mediocre, relying on unrealisitic overexposures, propagating the misrepresentation of “particles” and applying the selective ultra-precautionary approach.
However, one of their studies Amalia et al 2023 is of excellent quality: I reviewed it in Post 9 The authors examined particle mass concentrations in private homes in 4 European countries, in which one occupant is a vaper and the other a non-vaping spouse (with non-vaping homes as control). They collected bio-markers of vapers, passively exposed non-vapers and non-users. Their results show that save for a residual gasous PG and VG and a negligibly small increase in cotinine, a vaping environment is indistinguishable from a non-vaping one.
The reviewed study.
Particulate matter in aerosols produced by two last generation electronic cigarettes: a comparison in a real-world environment. Pulmonology, 30(2), 137-144. https://doi.org/10.1016/j.pulmoe.2021.03.005
Summary
The authors (24 TackSHS Project Investigators) of this chamber study examined the environmental aerosol emissions from two low powered vaping devices. They found a very weak (even negligible) level of pollution measured by the particle number concentrations (PNC) of an aerosol whose half life time is below 20 seconds. The authors misrepresent the gas phase (which they did not examine) and, contrary to their own findings, they conclude that this very reduced pollution level “might” not be sufficient to decrease or remove harm to exposed bystanders. The present comment shows this risk assessment to be misleading and erroneous.
Description of the study
The two vaping devices were “Just Fog” and Juul. The authors measured PNC and mean half life (defined as time an aerosol remains measurable in the air). Tests were conducted in three consecutive days, one of them without ventilation in a 48 m3 laboratory. Two voluntaries vaped in the center of the room towards an instrument placed 2 m away, puffing 3 times as ‘warm up’ followed by 10 puffs in 4-6 min. PNC were measured (optical particle counter (OPC) model Profiler 212-2) for sizes (\mu m micrometers) >0.3, >0.5, >0.7 and >1.0.
Experimental results are displayed in the authors’ Figures 1 and 2, and tables 2, 3, 4. Figure 1 describes the time evolution of the particle number concentration (PNC) of two sequences of 10 puffs delivered by (presumably) each one of 2 vapers located at 2 meters in 4-6 minutes. The graph in the figure shows two sequences of 10 puffs, with each individual puff producing peaks of 500-900 particles/cm^3, with the peak of each puff decaying to almost background level in ~20 seconds (Figure 2). The authors mentioned having sampled background levels before the experiments, but do not report these background levels. These are their figures 1 and 2
Limitations of the OPC
The OPC model Profiler 212 used by the authors is unable to measure ultra-fine particles, since its measurable diameter sizes are in the range between 0.3-10.0 \mu m (micrometers)[1]. To detect and measure ultra-fine particles the authors should have used a Condensed Particle Counter or adapt the OPC for this purpose [2]. It is highly likely that the authors reported overestimated particle diameters and peak PNCs, a known problem of optically based instruments in aerosols whose particles rapidly evaporate [3], which explains why they are not normally used in chamber studies of vaping emissions
To assess the limitations from the choice of the OPC, it is useful to compare this study with two other chamber emission studies with similar design [4, 5], which used different instruments that were well calibrated. Unfortunately, the authors do not mention any instrument calibration of the OPC. In what follows I describe the two comparative studies
Zhao et al [4]. Puffing protocol: 3 s puffs every 30 s in an 80 m^3 room. Three sessions: 10 min before vaping, 10 min during vaping (20 puffs) and 10 after vaping. Instruments: Condensation Particle Counter and DustTrak Aerosol Monitor (carefully calibrated) placed at 0.8 m, 1.5 m, 2.0 m and 2.5 m from the exhaling vaper. Background level (first 10 minutes session) 6.30 X 10^3/cm^3. The results in the vaping session varied with distance to the vaper:
At 0.8 m PNC increased in the first puff (of 20) to 10^5/cm^3, decaying in 20 s to 1.07 X 10^4/cm^3 (10% of peak value). Same pattern occurred for the remaining 19 puffs. In the 10 minutes after vaping PNC decreased to 7.94 X 10^3/cm^3 (15% above background), a slower decay because the accumulation of 20 rapid puffs increases environmental partial pressure that slows evaporation.
At 1.5 m: Same pattern as in 0.8 m with much lower PNC peaks: 1.34 X 10^4/cm^3 (time average 8.87 X 10^4/cm^3, less than half of that at 0.8 m).
At 2.0 m mean PNC was 2.05 X 10^3/cm^3, at 2.5 m 1.26 X 10^3/cm^3. These values are respectively 12% and 7% of the values at 0.8 m, comparable with the background levels before vaping.
Martuzevicius et al [5]. Volunteers puffed every 30 s for 5 times without restriction on puff duration in a chamber of 35.8 m^3. Background levels before vaping < 300/cm^3. The sampling point was in a heated mannequin simulating a bystander, at 2 m from the volunteer, with measurements at 0.5 and 1.0 m. Instruments: fast mobility particle sizer and electrical low pressure impactor, both operating with resolution of 1 second. Bimodal particle size distribution at 0.5 m with a modes 150 nm and 30 nm, flattening as vaping proceeded with larger mode shifting to lower values, at 2 m it is almost flat
The time evolution of PNC follows the same seesaw pattern as Zhao et al, with slightly higher peaks reaching 3 X 10^6/cm^3 at 0.5 m, ~10^5/cm^3 at 1 m, in all cases returning to background levels ~10^3/cm^3 in 15 s after the puff. At 2 m the aerosol is practically indistinguishable from the background, an effect likely aided by the mixing ventilation that lowers partial pressure and removes gas phase compounds, thus facilitating evaporation and dispersion.
The bimodal distributions with models around 150 nm in both [4,5] practically confirm the limitations un particle counts from the OPC. The results of these experiments roughly coincide with the authors’ Figure 1 and the mean half life around 20 s, though it is also possible that the 500-900/cm^3 peaks are over-estimations, but in what follows I will assume these values.
Misunderstanding of the aerosol short half life
The authors report a very short half life (n Figure 2) for both tested devices, emphasizing that the Juul generated lower PNC and had more rapid half life (10-20 seconds). However, the authors’ explanation of these results is flawed
“This very short half life is probably due to the reaction pathways of compounds that are attributed to PG and glycerol during the thermal decomposition of PG and glycerol in e-liquid solvents.
The thermal decomposition reactions of PG and glycerol occur when the aerosol is generated just before it is inhaled, not when it is exhaled into the environment (which is typically much colder and drier than inside the respiratory tracts). The short half life follows from the physical properties of liquid droplets that form the particulate phase of glycol based aerosols evolving along a relatively dry environment [6], as is the case with liquid droplets of the exhaled vaping aerosol that are composed almost exclusively of propylene glycol (highly volatile), glycerol, nicotine and water [7,8].
Misrepresentation of the gas phase
To assess the exposure risk that could follow from their experimental results the authors also misrepresent the gas phase of e-cigarette aerosols in general
The e-cigarette aerosol may be composed of a number of potentially harmful compounds in the gaseous phase such as acetone, benzaldehyde, methacrolein, acetaldehyde, 2-propenol, as well as the BTEX compounds.” [16—19]
other studies15---24 have demontrated that several other gaseous phase compounds, some of which are carcinogenic (such as formaldehyde) may be generated.
None of the 10 studies cited by the authors (references 15 to 24) to justify these statements is applicable to the authors’ experiment, none of them examined environmental aerosol exhaled by users of e-cigarettes, all conducted experiments on machine generated aerosols whose emissions can be conceived (at best) as a proxy for the inhaled aerosol, not for the exhaled one. Also, the main compounds of the inhaled aerosol are overwhelmingly retained (> 80%) by the users respiratory system: propylene glycol, glycerol, nicotine [9], including 97% of aldehydes [10].
The gas phase of exhaled aerosols was investigated by van Drooge et al [11] (which I reviewed in Post 9). These authors measured gas phase compounds in an atmosphere generated by 5 volunteers in a volume of 146 m^3 during 12 hour long daily sessions, comparing measured compounds with same compounds in the same space without vaping. This is a much robust and realistic approach than regimented puffing in chamber studies. They report negligible concentrations, comparable to non-vaping atmosphere, of PAHs (polycyclic aromatic hydrocarbons) and most VOCs (volatile organic compounds). Formaldehyde is the only compound that shows an increase in the vaping atmosphere (from 7.4 \mu g/m^3 to 14 \mu g/m^3 micrograms per cubic meter), a formaldehyde level compatible with non-smoking indoor environments in the European Union and well below the safety limits of the WHO.
Questionable assessment of health effects.
Considering their experimental results the authors state the following risk assessments in their public health perspective
The reduction of environmental pollution from the short half life of the Juul may not be sufficient to eliminate or to reduce the risk to the health of users and to the people involuntarily exposed to the aerosol of e-cigs, especially in public indoor environments.”
Considering this topic from a public health perspective, though both devices emit very small PM, potential harmful effects have to be taken into account, particularly for vulnerable populations, such as children, older people or chronic patients; moreover, repeated exposures to e-cig in real life conditions are still possible, especially in poorly ventilated, overcrowded enclosed spaces such as bars and discos.
These risk assessments read as voluntaristic statements without even an attempt to relate the authors’ experimental outcomes (short half life) to any toxicological reference. The fact that the aerosol rapidly evaporates (short half life) leads to a short time of bystander exposure, which has important toxicological implications.
The authors’ statements are also inconsistent by failing to distinguish between different indoor environments. It is very unlikely that children, older people or chronic patients will be willing to spend time in poorly ventilated, overcrowded enclosed spaces such as bars and discos. E-cigarettes are consumer products for exclusive usage of healthy adults. Should a risk assessment of adult usage consumer products be based primarily on health concerns relevant only for children and vulnerable sub-populations? Evidently, an environmental risk assessment of adult consumer products must distinguish between indoor venues that cater for adult public and venues with high occupancy of children and vulnerable individuals.
Although the authors’ experimental results (and those of [5,6]) were obtained under laboratory controlled conditions, they do suggest that the combined aerosol generated by few vapers puffing low powered devices represents a significantly small (even negligible) contribution to pollution levels in non-smoking indoor spaces in which occupants are exposed to other polluting aerosols besides vaping aerosols. This very small contribution to indoor pollution also holds in spaces with high occupancy, as long as the aerosol is generated by a rationally small number of vapers making a small minority of occupants. This is a very different situation from vape shops or a vape festivals, events in where dozens of vapers are vaping jointly (some with high powered devices) in the same site, but visiting a vape shop or attending a vape festival are episodic, not frequent, usage conditions.
Comparison with UFPs from other pollutants in non-smoking indoor environments
Since the authors only quantified UFPs, it is useful to compare qualitatively their experimental results with available evidence on measured UFP levels in homes, schools, offices and hospitality venues. As shown in extensive literature reviews [12,13], particles in indoor spaces can originate from outdoors (penetration of combustion originated particles, reactions form gas phase precursor), as well as a wide variety of indoor sources, including occupants activities (cooking, cleaning, smoking, candle lightning, vacuum cleaning, odorizers), as well as from building material, paintings, upholstery, carpets, even pets and the human body. The exhaled vaping aerosol is only one source of indoor pollution, likely among the weakest of all pollutants.
The two reviews [12,13] report UFP levels in homes, offices, schools and day care centers that are well above the levels reported by the authors and by [5,6]. For cooking activities lasting 10-210 minutes peak number concentrations ranged between 1.6 X 10^4/cm^3 to 6.3 X 10^5/cm^3. PNC concentrations often exceeding 105/cm3 with emission rates of 10^{12} particles/min have been measured [14] in home cooking on gas, electric stoves and electric toaster. Measured PNC levels in most visited restaurants reached high levels of 50,000–200,000 particles/cm^3 for the full 1 hour length of the meal [14,15].
We might argue that the authors’ idealized laboratory experiment should not be compared with cooking activities or with indoor spaces like restaurants and bars, but with indoor spaces in which UFP levels are expected to be much lower, specially indoor spaces in which a large share of occupants could be children, pregnant women, older and/or frail individuals, such as non-smoking private homes in developed countries, primary schools and nurseries. However, as we show below, even in such indoor spaces occupants are exposed to UFP levels higher than those obtained in the authors’ experimental results.
Private homes. Two comparable studies reviewed in [12,13] on seven single family houses and four apartments (considered same diameter range of UFPs) reported average concentration for indoor occupancy time of 16.1 X 10^3/cm^3 (range from 5.3 X 10^3/cm^3 to 34.7 X 10^3/cm3). A one year study on 24 couples in non-smoking houses in Italy [16], average PNC concentrations were in summer: 1.8 × 10^4/cm^3 (women), 9.2 × 10^4 /cm^3 (men) and in winter: 2.9 × 10^3/cm^3(women ), 1.3 × 10^4/cm^3 (men), Their figure 2 shows 24-h PNC trends in a house showing PNC between 3000/cm^3 and 5000/cm^3, peaking at 200,000/cm^3 in a cooking activity of 30 min.
A 500 day field study in 40 homes in Germany [17] measured average indoor PNC 8634/cm^3 (range 506/cm^3-641983/cm^3, 10564 hours observation), average outdoor PNC 6203 /cm^3 (range 1096/cm^3-17664^3/cm3, 11296 hours observation). Figure 3 of [17] shows the median diurnal time profile, with PNC clustering continuously around 3000/cm^3 in winter and around 5000/cm^3 in summer.
Indoor environments with children occupancy. In a review of 32 articles [18] with occupancy below age 18, 22 studies focused on UFP levels in children’s specific micro-environments, reports levels of mean personal exposure between 0.87 X 10^4/cm^3 and 6.20 X 10^4/cm^3, with the most frequent values between 1.00 X 10^4/cm^3 and 2.00 X 10^4/cm^3, with higher values reaching 1.46 X 10^4/cm^3 in children’s dwellings. See figure below
A review of 22 studies [19] found 5 comparable studies reporting mean UFP number concentrations between 5151/cm^3 to 29,100/cm^3, while two studies reported median values 14,700/cm^3 and 8203/cm^3. A review focused on primary schools [20] reported in classrooms PNC 1.56 X 10^3/cm^3 to 14.8 X 10^3/cm3, lower than in the ambient school environment 1.79 X 10^3/cm^3 to 24.1 X 10^3/cm^3. A Canadian cohort [21] including 352,966 children, with 30,825 children developing asthma during follow-up estimated mean prenatal and childhood UFP exposure to be 24,706/cm^3(interquartile range [IQR] = 3,785/cm^3) and 24,525/cm^3(IQR = 3,427/cm^3), respectively.
Risk assessment
Measured values in different non-smoking indoor environments show UFP levels well above (typically an order of magnitude above) the PNC levels found in the authors’ experiments (and in similar studies [5,6]). This summary of the literature includes also micro-environments with majority occupancy by children, all of which show UFP levels around 10^4/cm^3 above the maximal UFP measurement in the authors’ experiment 0.9 X 10^3/cm3. Therefore, available empiric evidence does not justify the authors concern on potential harm of children exposed to UFP levels found in their experiment
Besides particle numbers, the assessment of health risks from exposure to polluting aerosols must rely on the chemical composition of the pollutants. Part of UFP and PM indoor pollution originates from outdoor combustion sources, whose chemical composition is [12,13] predominantly complex carbonaceous compounds: organic carbon (OC) and elementary carbon (EC), together a wide variety off sulfates, nitrates, ammonium, metal oxides, sea salt, minerals. Part of indoor pollution originates from indoor sources (this is specially the case of UFPs), for example cooking activities that produce aerosols with large concentrations of PM and gases, all made of a complex organic chemical composition [22]: gas and PM, UFP, with main constituents saturated and unsaturated fatty acids, glycerides, sugars and their byproducts, aromatics, PAHs (polycyclic aromatic hydrocarbons), semi-volatile and volatile organic compounds (SVOCs, VOCs) and aldehydes, many of which are hazardous to health. As a contrast, exhaled vaping aerosols are more diluted than inhaled aerosols, since 97% of aldehydes and over 80% of the main constituent compounds (PG, VG, nicotine) are retained by the respiratory system [9,10]. As shown by van Drooge et al [11], the chemical composition of the exhaled vaping aerosol has a very low toxicity content, with close to the total aerosol mass made of PG, VG, nicotine and water [7,8].
Another important factor is the exposure time. Exposure to exhaled vaping aerosols is short timed and intermittent, as it only occurs when the vaper exhales (on average 15-20 minutes per day from 200 inhalation/exhalation cycles [23] lasting 5-6 seconds ). As a contrast, exposure to outdoor originated sources is continuous 24 h, while cooking aerosols involve higher concentration and higher toxicity content than in vaping aerosols and exposure is continuous lasting 10-210 minutes [12]. Assessing environmental health risks from indoor vaping requires looking carefully at these variables.
To reach in exhaled vaping aerosols UFP levels comparable to those above 104/cm3 measured in homes, schools, offices and hospitality venues requires abnormal conditions. Exposure to high PNC levels occurs when many vapers puff jointly in the same indoor space, for example around 10^4/cm^3 in vape shops [24] or much higher values in vape festivals with hundreds of vapers [25]. These exposures are episodic, infrequent and unrepresentative of everyday life vaping. Many chamber studies also use puffing protocols representing overexposures that bear no relation with puffing frequencies of consumer usage [26,27]. Finally, a very artificial way to produce overexposure is by placing a bystander very close (< 0.5 m) to the mouth of a vaper in the same direction of the exhaled jet, leading to exposure to PNC peaks up to 10^6/cm^3 [5,6] that rapidly decay, but this represents an extremely rude, involuntary and unlikely exposure that any bystander can avoid because the vaping jet is clearly visible. Also, vapers do not deliberately puff directly into the personal space of a bystander.
Conclusion
The authors’ experimental results show the exhaled aerosol from two low powered devices as a very weak pollutant, reaching PNC peaks of 500-900/cm^3 that rapidly decay (~ 20 seconds) background levels after each puff. These results are consistent with results of similar studies that have traced the spatial and temporal evolution of this aerosol [5,6]. As shown in a summary of evidence on UFPs in different indoor environments, including those with children occupancy, it is evident that their experimental results do not justify the authors’ strong precautionary assessment of vaping in indoor spaces, not in general and not regarding children and vulnerable individuals. Also, the authors’ risk assessment is selective and biassed because it only focuses on vaping in isolation, ignoring the fact that occupants of all non-smoking indoor spaces are also exposed to multiple sources of pollution from other aerosols generated by cooking, cleaning walls, painting, operating appliances, and also outdoor pollution penetrating indoors.
E-cigarettes are consumer products for exclusive usage by healthy adults. As with all consumer products for exclusive adult usage, their potential health effect on the most vulnerable individuals must be taken into consideration, but cannot be the only (or the primary) standard reference to evaluate their safety in general. In other words, indoor usage of e-cigarettes must be evaluated under their real usage conditions, specifically meaning an assessment to be applied primarily to the type of indoor environments that cater for adult patrons, such as restaurants, bars or work places, with appropriate regulations enforced to prevent usage in indoor spaces with vulnerable occupancy, while allowing a regulated indoor exposure of healthy adults as long as the exposure is voluntary.
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