ArticlePDF Available

Effect of Propylene Glycol and Vegetable Glycerine Ratio in E-Liquid on Aerosol Formation: Overview of Relevant Properties

  • Winge Group Electronics


Electronic nicotine delivery systems (ENDS) generate an aerosol by vaporising e-liquids that usually consist of propylene glycol (PG), vegetable glycerine (VG), and other ingredients (water, nicotine, and flavours). The chemical and physical properties of these components have a significant effect on aerosol formation and must be identified in order to improve product attractiveness and assess the degree of health risks. The aim of this article is to provide a description of the composition of the e-liquid base and its impact on the physical properties of the liquid used and the behaviour of the aerosol generated and particles separately. For this purpose, 46 articles were selected using a series of keywords. Englishlanguage publications were chosen. The impact of the PG/VG ratio on the physical properties of the e-liquid (boiling point, viscosity, volatility, hygroscopicity), aerosol emission characteristics (refractive index, light scattering coefficient, particle size distribution, concentration, emission of harmful compounds), vape attractiveness (taste, “throat-hit”, “cloud effect”), nicotine flux, coil temperature, and puff topography is presented. The PG/VG ratio is strongly correlated with the emission of carbonyls, which has adverse health effects and should be optimised. Furthermore, PG and VG also affect the other important characteristics of the aerosol generated by ENDS, which impact on both attractiveness and the consumption of harmful compounds. These findings could be considered for further research with the aim of improving electronic nicotine delivery systems as this can reduce levels of toxicants. This can be achieved by optimising the geometry of the components with respect to heating power and e-liquid.
Submitted | 13 April 2022 Accepted | 15 May 2022
Keywords | E-Liquid – Propylene Glycol – Vegetable Glycerine – Electronic Nicotine Delivery Systems
– Aerosol – Nicotine
Hokord Limited, Sheung Wan, Hong Kong Citation | Vyshneva, V. (2022). Effect of propylene glycol and vegetable
glycerine ratio in e-liquid on aerosol formation: Overview of relevant
properties. Adiktologie, 22 (2), 118–125.
Effect of Propylene Glycol and
Vegetable Glycerine Ratio in
E-Liquid on Aerosol Formation:
Overview of Relevant Properties
BACKGROUND: Electronic nicotine delivery systems
(ENDS) generate an aerosol by vaporising e-liquids
that usually consist of propylene glycol (PG),
vegetable glycerine (VG), and other ingredients
(water, nicotine, and flavours). The chemical and
physical properties of these components have a
signicant effect on aerosol formation and must be
identied in order to improve product attractiveness
and assess the degree of health risks. AIM: The
aim of this article is to provide a description of the
composition of the e-liquid base and its impact on
the physical properties of the liquid used and the
behaviour of the aerosol generated and particles
separately. METHODS: For this purpose, 46 articles
were selected using a series of keywords. English-
language publications were chosen. RESULTS: The
impact of the PG/VG ratio on the physical properties
of the e-liquid (boiling point, viscosity, volatility,
hygroscopicity), aerosol emission characteristics
(refractive index, light scattering coefcient, particle
size distribution, concentration, emission of harmful
compounds), vape attractiveness (taste, “throat-hit”,
“cloud effect”), nicotine flux, coil temperature, and
puff topography is presented. CONCLUSIONS: The
PG/VG ratio is strongly correlated with the emission
of carbonyls, which has adverse health effects and
should be optimised. Furthermore, PG and VG also
affect the other important characteristics of the
aerosol generated by ENDS, which impact on both
attractiveness and the consumption of harmful
compounds. These ndings could be considered for
further research with the aim of improving electronic
nicotine delivery systems as this can reduce levels
of toxicants. This can be achieved by optimising the
geometry of the components with respect to heating
power and e-liquid.
Corresponding author | Viktoriia Vyshneva, Hokord Limited, Ofce 212, Kwong Kee Building, 54–56
Jervois Street, Sheung Wan, Hong Kong
The popularity of electronic nicotine delivery systems (ENDS)
is growing rapidly worldwide as they produce fewer harmful
aerosols than conventional cigarettes do, since they do not
burn tobacco and fewer chemicals are delivered to the users’
bodies (Park & Choi, 2019).
The comparison between traditional tobacco cigarettes and
ENDS has been explored in a plethora of studies (Glantz &
Bareham, 2018; Glasser et al., 2017; Ward et al., 2020) which
conrm that electronic nicotine delivery systems are popularly
considered a less harmful alternative to traditional smoking,
which is represented as a product with a substantial health risk.
Increased attention to those systems has contributed to the rapid
progress of the design of the devices. The rst- generation elec-
tronic cigarettes are called “cigalikes”; they were designed like
traditional cigarettes, while the second- and third-generation
systems have changeable parts and their shape and design can
vary widely (Keamy-Minor et al., 2019; Pepper & Brewer, 2014).
Numerous studies have been performed to evaluate the toxi-
cological characterisation of vaping emission products, most of
which remark that the chemical composition of ENDS is less
harmful than traditional tobacco smoke (Belka et al., 2017;
Dutra & Glantz, 2014; Son et al., 2020; Ward et al., 2020).
However, vaped e-liquids can also generate substances that
may lead to the formation of toxic components, especially
carbonyls that are similar to those seen in conventional ciga-
rettes (Son et al., 2020). Such observations argue in favour of
continuing the study of the emission products of vape devices
(El-Hellani et al., 2018, Jiang et al., 2020; Kosmider et al., 2014;
Son et al., 2020). Additionally, a signicant part of the ndings
has been focused on the consideration of differences in the
impact on the human body of both ways of smoking (Park &
Choi, 2019).
The emissions produced by different kinds of smoking sys-
tems depend on the design features of the devices’ compo-
nents, which is why the understanding of the dependence of
some parameters of vape devices on others remains unclear
and must be further examined. This scientic interest is clearly
linked to the wide popularity of electronic nicotine delivery
systems, which, in turn, raises concerns about the possibil-
ity of adverse health effects in users and environmental haz-
ards (Marques et al., 2021). In addition, a preference for such
devices is questionable because of the use of vape devices by
nicotine-naive adolescents (Brett et al., 2021; Camenga et al.,
2014; Dutra & Glantz, 2014).
In general, vape devices utilise a battery-powered coil to aero-
solise an e-liquid that often contains nicotine and/or avouring
into an inhalable aerosol. This device is usually composed of
electrical components that include a battery, chip, wire, button,
and atomising components (a coil, wick, tank, and mouthpiece;
Gao et al., 2021).
First, the heater coil is activated during the puff and the liq-
uid surrounding the coil heats up and vaporises. The vapour
that has been formed comes in contact with the cold air and
is condensed to form an aerosol of ultrane particles that car-
ries nicotine deep into the lungs. Aerosol particles are rapidly
absorbed, then travel through the left heart, translocating to
the brain in a few seconds. They can coagulate and evaporate,
changing their size and behaviour suitably (Nides et al., 2014;
Yingst et al., 2019).
Certainly, the design of these components may inuence aero-
sol formation and delivery, which is one of the key parameters
in aerosol formation. Understanding the impact these charac-
teristics have on aerosol delivery at each stage may contrib-
ute to deepening our knowledge of the public health effects of
vape devices.
Another equally important parameter is the composition of the
e-liquid. The e-liquid usually contains a base that includes pro-
pylene glycol (PG) or vegetable glycerine (VG; or a mixture of
both) with or without the addition of avours, water, and nico-
tine (Uryupin et al., 2013). Variations in the ratios of the com-
ponents of the e-liquid can affect aerosol formation in different
ways, particularly in terms of particle size, visible effects, nic-
otine ux, etc. via the different chemical and thermodynamic
properties of the substances used.
Consequently, the aerosols generated from vape devices have
a signicant impact on the human respiratory system. This
is primarily related to the difference in the absorption of par-
ticles inside the human body with various sizes as a result of
the inuence of gravity, inertia, and Brownian motion. Hence,
small particles are affected by Brownian motion with the abil-
ity to penetrate into lungs, whereas large particles can only
settle in the upper respiratory tract via gravity (Manigrasso
et al., 2015). Probably, the medium-sized particles move with
air ow: inhale and exhale. Gaining a further understanding
of the properties of e-liquids, features of device components,
thermodynamic characteristics of the system, and other rele-
vant parameters may assist in answering questions about the
assimilation of aerosol particles pathing through airways and
their health effect (Oldham et al., 2018).
This review seeks to improve our understanding of the general
properties of PG and VG, features of their chemical structure,
and its effect on physical and chemical properties.
A literature review was performed to highlight the main
properties of e-liquids containing PG/VG and their effect
on various features. The research process was investigated
using Google Scholar as this database ensures a wide range
of articles. The research criteria were a combination of the
keywords “e-liquid”, “vegetable glycerine”, “propylene gly-
col”, “ENDS”, “aerosol”, and “nicotine”. Moreover, only articles
written in English were chosen. In general, 46 research arti-
cles were selected so as to highlight the main properties and
combine them in order to provide a broad understanding of
the characteristics of the substances used. Additionally, two
safety sheets were included to provide information about the
physical properties of PG and VG.
It has been observed that glycerine is not a harmful com-
pound. Therefore, the permissible dose of glycerol and pro-
pylene glycol in an aerosol is 10 mg/m3 for an exposure time of
eight hours, according to the Occupational Safety and Health
Administration (Jacob et al., 2018; Segur, 1953).
PG and VG have different properties, the combination of which
has an effect on the thermodynamic properties of the e-liquid.
The PG/VG ratio as a solvent system may have a signicant
impact on the behaviour of the aerosol particles and their inu-
ence on taste, nicotine ux, and other key parameters that are
determined by the viscosity, boiling point, volatility, and chem-
ical structure of VG and PG. The molecular weight and viscosity
of VG are greater than those of PG, meaning that the addition
of VG to the base contributes to increasing the viscosity of the
e-liquid (Talih et al., 2017). Therefore, the particles generated
with a high VG content of the e-liquid may aggregate into large-
sized particles because of their viscosity (Wu et al., 2021).
The situation related to boiling point is similar: the more VG
there is in the e-liquid, the higher the boiling point is. Much
attention should be paid to this because reaching boiling point
by means of the coil leads to evaporation of the e-liquid and phe-
nomena that occur during the vaporisation process and over-
heating cause the degradation of products, with the formation
of harmful compounds (Talih et al., 2017; Wright et al., 2016).
The main difference between PG and VG is their hygroscopicity
– the ability to absorb moisture from the ambient air or human
respiratory system. For VG this property is expressed in the
ability to accumulate or supply moisture until equilibrium with
the ambient relative humidity is established. The hygroscopic-
ity of the substances increases with the number of hydro-
philic groups in their molecular structure. For that reason the
hygroscopicity of VG is stronger than that of PG (the number of
hydrophilic groups is three and two, respectively). The molec-
ular structures of PG (C3H8O2) and glycerine (C3H8O3) are shown
in Figure 1 (a) and Figure 1 (b) respectively. Hygroscopicity could
lead to growing particle sizes and changing the conditions
under which the experiment is performed if test samples are
exposed to the air for some time (Segur, 1953; Wu et al., 2021).
An e-liquid consists of a solvent system (PG and VG) in which
other additives are dissolved in various mixture ratios. The
main qualities of those substances can be summarised as
shown in Table 1. The characteristics of each component of
the electronic liquids play a signicant role in the formation
of the aerosol; therefore, determination of the physical and
chemical properties is important in studying electronic nic-
otine delivery systems.
Propylene glycol is a colourless, odourless, non-turbid, vis-
cous liquid with a slightly sweet taste, the physical properties
of which are introduced in Table 1. It is easily miscible with a
range of solvents (water, acetone, chloroform, etc.; Jacob et al.,
2018; Technical Product Information, 2018). PG is a widely
used compound in many industries, such as the food and
tobacco industry, cosmetics, chemical intermediates, pharma-
ceuticals, paints and coatings, etc. In general, PG is classied as
a safe product according to the Food and Drug Administration
but it can irritate the respiratory tract and cause allergic reac-
tions (Kulhánek & Baptistová, 2020).
Glycerol is a clear, viscous, odourless, sweet-tasting hygroscopic
liquid that can be extracted from natural oils and therefore it
is called “vegetable glycerine” (Kulhánek & Baptistová, 2020).
Glycerol is a chemical compound, whereas glycerine refers
to commercial products that contain a percentage of water (a
glycerol-water solution). The physical properties of glycerol are
presented in Table 1. Glycerol is used in various applications,
including the pharmaceutical, plastics, and tobacco and food
industries, especially because of its useful solvent properties,
which allow it to combine solutions with water, methanol, etha-
nol, and glycol (Wernke, 2014).
Glycerine and its aqueous solutions have the following essen-
tial characteristics: low saturated vapour pressure; high hygro-
scopicity and boiling point; a decrease in density and viscosity
with an increase in temperature; less surface tension and spe-
cic heat of pure glycerine than water (Kulhánek & Baptistová,
2020; Segur, 1953).
Table 1 | General physical properties of glycerol and propylene glycol
Properties Units Glycerol Propylene Glycol
Density kg × m-3 1.261 1.036
Molecular weight g × mol -1 92.09 76.09
Viscosity Pa × s 1.49 0.0499
Boiling point C 290 187
Refractive index 1.47399 1.4329
Heat of vaporization kJ × kg -1 830 711
Specic heat capacity J × kg -1 × C -1 2350 2481
Surface Tension mN × m -1 63.4 26
Vapor pressure (20 C) kPa < 0.00033 0.0131
Effect of Propylene Glycol and Vegetable Glycerine Ratio in E-Liquid on Aerosol Formation: Overview of ... 120ADDICTOLOGY
The PG/VG ratio may affect the delivery of nicotine and actually
the taste. First of all, a larger ratio of PG can cause a “throat-hit”
effect associated with more nicotine delivery (Li et al., 2016). In
contrast, a larger ratio of VG leads to “cloud effects”. The “cloud
effects” phenomenon inuences product attractiveness, which,
therefore, leads to consumers buying products with more artis-
tic-looking exhaled aerosols more frequently (Brett et al., 2021).
Meanwhile, the “throat-hit” is associated with satisfaction and
the dependence on vaping because of the high nicotine ux in
the e-liquid containing PG (Etter, 2016; Goldenson et al., 2016).
This behaviour is the cause of the physical properties of the
components, in particular, optical properties, particle size, and
aerosol concentration.
One of the most signicant characteristics that should be taken
into account in aerosol particle analyses is the optical prop-
erties of the aerosol generated from the e-liquid. One of the
important parameters is the refractive index, which includes
real and imaginary parts reecting the light-scattering and light
absorption properties of the aerosol particles (Ingebrethsen et
al., 2012; Liu et al., 2015).
Neither PG nor VG absorbs in the visible spectrum wavelength
(400-780 nm), and thus they have a small imaginary part of the
refractive index (n→0) (Baassiri et al., 2017). It must be noted
that the real part of the refractive index is larger for VG than PG
for the visible wavelength range, inuencing more foggy “cloud
effects” of the aerosol generated from e-liquids with a higher
VG content (Wu et al., 2021). Baassiri et al. (2017) measured
the refractive index of a PG/VG solution with various PG/VG
ratios. They investigated the accretion of refractive index with
an increasing VG content. Moreover, they explored the effect
of the composition of the liquid on the light-scattering coef-
cient, and established that for 100:0 VG:PG this coefcient is
less than in the case of a 0:100 VG/PG ratio.
In contrast, the mass concentration of the measured total par-
ticulate matter (TPM) in the lters increases with an increasing
PG/VG ratio. It means that the more PG there is in the e-liquid,
the more concentrated the aerosol is. In that case, it is expected
that a more evident “cloud effect” will be seen, which contra-
dicts the preliminary conclusions. The aerosol generated by
an e-liquid containing more propylene glycol consists of par-
ticles smaller than that generated by an e-liquid containing
more glycerol. Nevertheless, there are two explanations for
that effect. Firstly, the lower vapour pressure of VG affects the
slower evaporation process of particles with a high VG content,
which leads to “long-lived” aerosol clouds. Secondly, an aerosol
with a higher PG content has a lower light-scattering coefcient
(Baassiri et al., 2017).
The reason for most of the effects is the volatility of the sub-
stances under study. The volatility of substances has been
associated with vapour pressure: the low vapour pressure of
VG causes less volatility. Such observations help draw the con-
clusion that a liquid with a greater PG ratio evaporates more
rapidly than a liquid with a greater VG content. Of course, it is
also affected by the enthalpy of vaporisation and specic heat
but since these parameters are almost equal for PG and VG, the
volatility could be only determined by vapour pressure. The
main reason for this behaviour is the difference in molecular
structure. The point is that VG has one more OH group than PG,
which leads to stronger hydrogen bond intermolecular forces
in the e-liquid solution (Li et al., 2021). E-liquid could contain
water, which characteristics must also be taken into account.
Water is more volatile than PG but has greater specic heat
Figure 1 | Molecular structure of propylene glycol (C3H8O2) Figure 2 | Molecular structure of glycerine (C3H8O3)
capacity than PG at a given temperature. Hence, more energy
must be input to evaporate water with the same rate as PG
does. Consequently, PG evaporates faster than water anyway
(Baassiri et al., 2017).
The composition of the e-liquid also has an inuence on the
aerosol dynamics. Li et al. (2020) illustrated the correlation
between the particle loss rate and PG/VG ratio. In general,
the particle loss rate increases with a rise in the PG/VG ratio
from 0:100 to 100:0 without nicotine content, while adding
nicotine promotes the reverse behaviour. The reason for this
behaviour may be the saturated vapour pressure of nicotine,
which could impact on the overall e-liquid saturation vapour
pressure (Li et al., 2020).
The PG/VG ratio affects the nicotine ux. The nicotine ux
is the rate at which the aerosol is emitted from a vape device
per unit of time (Eissenberg & Shihadeh, 2015). That param-
eter is used as a potential regulatory value, being an essential
factor that can inuence the perception of aerosol emission
by users. Separately, Talih et al. (2017) previously showed
that an e-liquid with a higher PG content transports more
nicotine than an e-liquid with a higher VG content because of
its threshold for evaporation and therefore greater volatility.
Thus, PG may be called a vehicle of nicotine (Lechasseur et al.,
2019). That phenomenon is related to the “throat-hit” effect
that was discussed above (Baassiri et al., 2017). Spindel et al.
(2018) conrmed that a pure PG liquid or 55PG:VG delivered
more nicotine than an e-liquid containing VG. In that nding
users took shorter puffs using devices with PG content than
VG content but they obtained a higher plasma nicotine con-
centration (Spindle et al., 2018). Talih et al. (2017) described
a transport model that clearly explains the observation of
greater TPM emissions and nicotine in an e-liquid with a
high PG content and therefore conrmed the assumption of
greater nicotine transfer by PG (Talih et al., 2017).
Another important characteristic that is inuenced by the PG/
VG ratio is the particle size distribution. The particle size dis-
tribution may be measured by various techniques (Belka et al.,
2017; Fuoco et al., 2014; Ingebrethsen et al., 2012; Oldham et
al., 2018). Baassiri et al. (2017) showed that a PG-dominant
e-liquid emits smaller particles than a VG-dominant e-liquid
but, at the same time, the number of particles is greater in the
rst case. Identical results were obtained by Zhang et al. (2013).
Pourchez et al. (2018) also found that a high-PG e-liquid gen-
erates smaller particles than a high-VG e-liquid at low wattage,
while reaching 22 W leads to their convergence. Moreover,
Zervas et al. (2018) noticed that the particle size distribution
of propylene glycol gives a linear size distribution. In contrast,
the distributions of VG and a mixture of PG and VG have some
peaks that are connected to the high boiling point of glycerine
compared to PG.
VG and PG undergo decomposition to molecular carbonyl
compounds at high temperatures (Jiang et al., 2020; Y. Li et al.,
2021). El-Hellani et al. (2018) showed that there is no corre-
lation between the PG/VG ratio and the formation of carbon-
yls. But Kosmider et al. (2014) found that high-PG-level liquids
generate more carbonyls than VG-based e-liquids. The levels
of formaldehyde, acetaldehyde, and acetone are dramatically
increased with a higher PG content for a certain range of bat-
tery output voltage. This is particularly clear for a high bat-
tery output voltage, which indicates that the level of carbonyls
increases with increased battery output voltage, as it leads to
a higher coil temperature (Kosmider et al., 2014). Y. Li et al.
(2021) also found that some carbonyl degradation products
dramatically decreased with an increasing VG fraction in the
e-liquid but the fraction of acrolein rose in that case. Conklin et
al. (2018) conrmed that PG generates a higher level of acetal-
dehyde and crotonaldehyde, whereas VG leads to higher levels
of formaldehyde and the formation of the unsaturated aldehyde
acrolein. Moreover, they indicated that lower levels of carbonyls
were emitted by a mixture with a 25PG:75VG ratio, which indi-
cates that some proportions of PG and VG can reduce the level
of carbonyls. Such observations may be related to heat trans-
fer, which is strongly correlated with the chemical and physi-
cal properties of the components of e-liquids discussed above
(Talih et al., 2017). The emission of carbonyls is one of the key
parameters as it has adverse health effects. For instance, for-
maldehyde and acetaldehyde are classied as potential car-
cinogenic substances. Acrolein has a strong irritating effect
on the mucous membranes of the eyes and respiratory tract.
Overall, these compounds are potentially hazardous and their
consumption may be regulated by the PG/VG ratio or optimis-
ing the device’s characteristics.
Thus, the thermal degradation of products is the effect of the
coil temperature, which is determined by the composition of
the e-liquid. The coil temperature may also be inuenced by
the PG/VG ratio and the addition of avours, nicotine, and
water, which could change the heat capacity, boiling point, vis-
cosity, airow, and other relevant characteristics. For instance,
Korzun et al. (2018) noticed that the solvent consumption of
an e-cigarette increases signicantly with increased airow,
which could be a reason for the faster cooling effect. It may also
be assumed that the delivery of the e-liquid to the heating zone
occurs faster with a high PG content. In general, the charac-
teristics of coils and their dependence on devices’ parameters
have been examined in a number of studies (Saleh et al., 2020;
Y. Li et al., 2021; Zhao et al., 2016) but further research is still
needed, especially regarding the inuence of the composition
of the liquid on the coil temperature.
It is also noteworthy that the PG/VG ratio was found to have
an impact on the puff topography via taking larger and longer
puffs using a VG-based e-liquid in order to bring more nicotine
(Y. Li et al., 2021) However, the puff volume and puff duration
were not controlled, thus bringing the results obtained into
question. Therefore, that research study should be repeated in
order to gain accurate results.
A number of the properties that were discussed above may
have a huge impact on the taste experienced by the user.
Undoubtedly, the PG/VG ratio determines the particle size and
therefore its absorption. To be exact, the particles generated
by a VG-based e-liquid are mainly large, sweet, and with the
property of adhesion. On the other hand, e-liquids with a high
PG ratio emit particles with a clearly “true” taste because of the
small particle size, which penetrates into the alveoli.
Effect of Propylene Glycol and Vegetable Glycerine Ratio in E-Liquid on Aerosol Formation: Overview of ... 122ADDICTOLOGY
Overall, the composition of the e-liquid is the essential param-
eter in vape emission characteristics. This study highlighted
the features that have been determined by the VG and PG ratios
and their impact on the properties of the aerosol that is formed.
The attractiveness of vape devices (“cloud effect” and “throat-
hit”) is inuenced by the PG/VG ratio. The “throat-hit” is linked
to the possibility of PG evaporating rapidly compared to VG,
while the chemical structure and capacity to generate particles
with a greater refractive index and light-scattering coefcient
of VG leads to clear visual effects that are preferred by users.
The properties of PG and VG described in this study help to
establish a link between the thermodynamic properties of the
e-liquid and transport phenomena during vaping that regu-
late the quantity of thermal degradation products in general.
On the basis of this fact, the most important eld of the impact
of the PG/VG ratio is the emission of carbonyls, as their action
is directly related to the user’s health. Formaldehyde, acetal-
dehyde, acrolein, and other compounds have adverse health
effects such as causing damage to the lining of the lungs and
irritation of the mucous membrane and can also cause cancer,
etc. The regulation of the PG/VG ratio may reduce the emission
of these compounds and thereby minimise the risk to users’
health. The selection of the safest PG/VG ratio could be investi-
gated with deep knowledge of the chemical and physical prop-
erties of PG, VG, and heat transfer parameters.
Further study of the dependencies of the base components
of e-liquids and other device characteristics is important in
research into electronic nicotine delivery systems. The attrac-
tiveness and health safety of ENDS are essential aspects of
the vaping industry and both of them are regulated by the PG/
VG ratio. In addition, other features play a signicant role in
aerosol formation and its composition, for instance, heating
element characteristics. The optimisation of heating element
characteristics and the composition of the e-liquid is a way of
improving vaping devices.
Broadly speaking, the properties described above are deter-
mined not only by the PG/VG ratio, but also by the addition
of avours and nicotine. Consequently, studying aspects of
their impact is also important in studying the emissions from
vape devices.
Declaration of interest: No conflict of interest.
Baassiri, M., Talih, S., Salman, R., Karaoghlanian, N., Saleh, R., El Hage,
R., Saliba, N., & Shihadeh, A. (2017). Clouds and “throat hit”: Effects of
liquid composition on nicotine emissions and physical characteristics of
electronic cigarette aerosols. Aerosol Science and Technology, 51 (11),
Belka, M., Lizal, F., Jedelsky, J., Jicha, M., & Pospisil, J. (2017).
Measurement of an electronic cigarette aerosol size distribution during
apuff. EPJ Web of Conferences, 143.
Brett, E., Krissinger, R., & King, A. (2021). The rise and fall of e-cigarette
cloud chasing appealing to youth. Preventive Medicine Reports, 24,
Article 101644.
Camenga, D. R., Delmerico, J., Kong, G., Cavallo, D., Hyland, A.,
Cummings, K. M., & Krishnan-Sarin, S. (2014). Trends in use of electronic
nicotine delivery systems by adolescents. Addictive Behaviors, 39 (1),
Conklin, D. J., Ogunwale, M. A., Chen, Y., Theis, W. S., Nantz, M. H., Fu, X.
A., Chen, L. C., Riggs, D. W., Lorkiewicz, P., Bhatnagar, A., & Srivastava, S.
(2018). Electronic cigarette-generated aldehydes: The contribution of
e-liquid components to their formation and the use of urinary aldehyde
metabolites as biomarkers of exposure. Aerosol Science and Technology,
52 (11), 1219–1232.
Dutra, L. M., & Glantz, S. A. (2014). Electronic cigarettes and conventional
cigarette use among US adolescents: A cross-sectional study.
JAMA Pediatrics, 168 (7), 610–617.
Eissenberg, T., & Shihadeh, A. (2015). Nicotine flux: A potentially
important tool for regulating electronic cigarettes. Nicotine and Tobacco
Research, 17 (2), 165–167.
El-Hellani, A., Salman, R., El-Hage, R., Talih, S., Malek, N., Baalbaki, R.,
Karaoghlanian, N., Nakkash, R., Shihadeh, A., & Saliba, N. A. (2018).
Nicotine and carbonyl emissions from popular electronic cigarette
products: Correlation to liquid composition and design characteristics.
Nicotine and Tobacco Research, 20 (2), 215–223.
Etter, J. F. (2016). Throat hit in users of the electronic cigarette: An
exploratory study. Psychology of Addictive Behaviors, 30 (1), 93–100.
Fuoco, F. C., Buonanno, G., Stabile, L., & Vigo, P. (2014). Influential
parameters on particle concentration and size distribution in the
mainstream of e-cigarettes. Environmental Pollution, 184, 523–529.
Gao, Y., Li, D., Ru, J., Yang, M., Lu, L., Lu, L., Wu, J., Huang, Z., Xie, Y., &
Gao, N. (2021). A numerical study on capillary-evaporation behavior
of porous wick in electronic cigarettes. Scientic Reports, 11 (1), 1–11.
Glantz, S. A., & Bareham, D. W. (2018). E-Cigarettes: Use, effects onsmoking,
risks, and policy implications. Annual Review of Public Health, 39, 215–235.
Glasser, A. M., Collins, L., Pearson, J. L., Abudayyeh, H., Niaura, R. S.,
Abrams, D. B., & Villanti, A. C. (2017). Overview of electronic nicotine
delivery systems: A systematic review. American Journal of Preventive
Medicine, 52 (2), e33–e66.
Goldenson, N. I., Kirkpatrick, M. G., Barrington-Trimis, J. L., Pang, R.
D., McBeth, J. F., Pentz, M. A., Samet, J. M., & Leventhal, A. M. (2016).
Effects of sweet flavorings and nicotine on the appeal and sensory
properties of e-cigarettes among young adult vapers: Application of a
novel methodology. Drug and Alcohol Dependence, 168, 176–180.
Ingebrethsen, B. J., Cole, S. K., & Alderman, S. L. (2012). Electronic cigarette
aerosol particle size distribution measurements. Inhalation Toxicology,
24 (14), 976–984.
Jacob, S. E., Scheman, A., & McGowan, M. A. (2018).
Propylene glycol. Dermatitis, 29 (1), 3–5.
Jiang, H., Ahmed, C. M. S., Martin, T. J., Canchola, A., Oswald, I. W. H.,
Garcia, J. A., Chen, J. Y., Koby, K. A., Buchanan, A. J., Zhao, Z., Zhang, H.,
Chen, K., & Lin, Y. H. (2020). Chemical and toxicological characterization
of vaping emission products from commonly used vape juice diluents.
Chemical Research in Toxicology, 33 (8), 2157–2163.
Keamy-Minor, E., McQuoid, J., & Ling, P. M. (2019). Young adult
perceptions of JUUL and other pod electronic cigarette devices in
California: A qualitative study. BMJ Open, 9 (4), 1–7.
Korzun, T., Lazurko, M., Munhenzva, J., Barsanti, K. C., Huang, Y., Jensen,
R. P., Escobedo, J. O., Luo, W., Peyton, D. H., & Strongin, R. M. (2018).
E-cigarette airflow rate modulates toxicant proles and can lead to
concerning levels of solvent consumption. ACS Omega, 3 (1), 30–36.
Kosmider, L., Sobczak, A., Fik, M., Knysak, J., Zaciera, M., Kurek, J., &
Goniewicz, M. L. (2014). Carbonyl compounds in electronic cigarette vapors:
Effects of nicotine solvent and battery output voltage. Nicotine and Tobacco
Research, 16 (10), 1319–1326.
Kulhánek, A., & Baptistová, A. (2020). Chemical composition of electronic
cigarette e-liquids: Overview of current evidence of toxicity. Adiktologie,
20 (3–4), 137–144.
Lechasseur, A., Altmejd, S., Turgeon, N., Buonanno, G., Morawska, L.,
Brunet, D., Duchaine, C., & Morissette, M. C. (2019). Variations in coil
temperature/power and e-liquid constituents change size and lung
deposition of particles emitted by an electronic cigarette. Physiological
Reports, 7 (10).
Li, L., Lee, E. S., Nguyen, C., & Zhu, Y. (2020). Effects of propylene glycol,
vegetable glycerin, and nicotine on emissions and dynamics of electronic
cigarette aerosols. Aerosol Science and Technology, 54 (11), 1270–1281.
Li, Q., Zhan, Y., Wang, L., Leischow, S. J., & Zeng, D. D. (2016). Analysis of
symptoms and their potential associations with e-liquids’ components: a
social media study. BMC Public Health, 16, Article 674, 1–12.
Li, Y., Burns, A. E., Tran, L. N., Abellar, K. A., Poindexter, M., Li, X.,
Madl, A. K., Pinkerton, K. E., & Nguyen, T. B. (2021). Impact of e-liquid
composition, coil temperature, and puff topography on the aerosol
chemistry of electronic cigarettes. Chemical Research in Toxicology,
34 (6), 1640–1654.
Liu, H., Ye, J., Yang, K., Xia, M., Guo, W., & Li, W. (2015). Real part of
refractive index measurement approach for absorbing liquid. Applied
Optics, 54 (19), Article 6046.
Manigrasso, M., Buonanno, G., Fuoco, F. C., Stabile, L., & Avino, P. (2015).
Aerosol deposition doses in the human respiratory tree of electronic
cigarette smokers. Environmental Pollution, 196, 257–267.
Nides, M. A., Leischow, S. J., Bhatter, M., & Simmons, M. (2014). Nicotine
blood levels and short-term smoking reduction with an electronic
nicotine delivery system. American Journal of Health Behavior, 38 (2),
Effect of Propylene Glycol and Vegetable Glycerine Ratio in E-Liquid on Aerosol Formation: Overview of ... 124ADDICTOLOGY
Oldham, M. J., Zhang, J., Rusyniak, M. J., Kane, D. B., & Gardner, W. P.
(2018). Particle size distribution of selected electronic nicotine delivery
system products. Food and Chemical Toxicology, 113, 236–240.
Park, M. B., & Choi, J. K. (2019). Differences between the effects of
conventional cigarettes, e-cigarettes and dual product use on urine
cotinine levels. Tobacco Induced Diseases, 17 (12), 1–9.
Pepper, J. K., & Brewer, N. T. (2014). Electronic nicotine delivery system
(electronic cigarette) awareness, use, reactions and beliefs: A systematic
review. Tobacco Control, 23 (5), 375–384.
Polkadot. (n.d.). An updated overview of polkadot.
Pourchez, J., Parisse, S., Sarry, G., Perinel-Ragey, S., Vergnon, J. M.,
Clotagatide, A., & Prévôt, N. (2018). Impact of power level and rell liquid
composition on the aerosol output and particle size distribution generated
by a new-generation e-cigarette device. Aerosol Science and Technology,
52 (4), 359–369.
Saleh, Q. M., Hensel, E. C., & Robinson, R. J. (2020). Method for
quantifying variation in the resistance of electronic cigarette coils.
International Journal of Environmental Research and Public Health,
17 (21), 1–16.
Segur, J. (1953). Physical properties of glycerol and its solutions.
Glycerine Producers’ Association.
Son, Y., Bhattarai, C., Samburova, V., & Khlystov, A. (2020). Carbonyls and
carbon monoxide emissions from electronic cigarettes affected by device
type and use patterns. International Journal of Environmental Research
and Public Health, 17 (8).
Spindle, T. R., Talih, S., Hiler, M. M., Karaoghlanian, N., Halquist, M. S.,
Breland, A. B., Shihadeh, A., & Eissenberg, T. (2018). Effects of electronic
cigarette liquid solvents propylene glycol and vegetable glycerin on user
nicotine delivery, heart rate, subjective effects, and puff topography.
Drug and Alcohol Dependence, 188, 193–199.
Talih, S., Balhas, Z., Salman, R., El-Hage, R., Karaoghlanian, N., El-Hellani,
A., Baassiri, M., Jaroudi, E., Eissenberg, T., Saliba, N., & Shihadeh, A.
(2017). Transport phenomena governing nicotine emissions from
electronic cigarettes: Model formulation and experimental investigation.
Aerosol Science and Technology, 51 (1), 1–11.
Technical Product Information. (2018). Propylene Glycol (PG) CAS
number. Monument Chemical.
Uryupin, A. B., Peregudov, A. S., Kochetkov, K. A., Bulatnikova, L. N.,
Kiselev, S. S., & Nekrasov, Y. S. (2013). Qualitative and quantitative
compositions of fluids for electronic cigarettes. Pharmaceutical
Chemistry Journal, 46 (11), 687–692.
Ward, A. M., Yaman, R., & Ebbert, J. O. (2020). Electronic nicotine
delivery system design and aerosol toxicants: A systematic review. PLoS
ONE, 15 (6), 1–22.
Wernke, M. J. (2014). Glycerol. In P. Wexler (Ed.), Encyclopedia of
toxicology (3rd ed., pp 754–756).
Wright, T. P., Song, C., Sears, S., & Petters, M. D. (2016). Thermodynamic
and kinetic behavior of glycerol aerosol. Aerosol Science and Technology,
50 (12), 1385–1396.
Wu, J., Yang, M., Huang, J., Gao, Y., Li, D., & Gao, N. (2021). Vaporization
characteristics and aerosol optical properties of electronic cigarettes.
Environmental Pollution, 275, Article 116670.
Yingst, J. M., Hrabovsky, S., Hobkirk, A., Trushin, N., Richie, J. P., & Foulds,
J. (2019). Nicotine absorption prole among regular users of a pod-based
electronic nicotine delivery system. JAMA Network Open, 2 (11), Article
Zervas, E., Litsiou, E., Konstantopoulos, K., Poulopoulos, S., &
Katsaounou, P. (2018). Physical characterization of the aerosol of an
electronic cigarette: Impact of rell liquids. Inhalation Toxicology, 30 (6),
Zhang, Y., Sumner, W., & Chen, D. R. (2013). In vitro particle size
distributions in electronic and conventional cigarette aerosols suggest
comparable deposition patterns. Nicotine and Tobacco Research, 15 (2),
Zhao, T., Shu, S., Guo, Q., & Zhu, Y. (2016). Effects of design parameters
and puff topography on heating coil temperature and mainstream
aerosols in electronic cigarettes. Atmospheric Environment, 134, 61–69.
ResearchGate has not been able to resolve any citations for this publication.
Full-text available
Electronic cigarette (e-cigarette) use continues to rise among youth with new devices and technology outpacing regulation. The “cloud chasing” phenomenon, whereby vapers compete or otherwise showcase the production of large or artistic exhaled aerosols from e-cigarettes, played a role in the early appeal of e-cigarette use in youth. This paper describes the sudden rise in the phenomenon of cloud chasing on social media and at vaping conventions due to the proliferation of second and third-generation powerful e-cigarette devices in their peak in 2015 and then their subsequent decline in the past few years. We describe four distinct factors that affected both the rise and fall in cloud chasing, including: 1) the rapid evolution of powerful e-cigarette devices, 2) the increase in social media promotions, 3) an inability of regulatory bodies to keep up with evolving ENDS technology, and 4) two recent widespread health concerns and conditions. Conclusions highlight the importance of swift regulation and effective health communication to mitigate unintended consequences of product evolution. It remains unknown whether such vape tricks and related competitions will reemerge and appeal to youth as store fronts reopen and devices continue to evolve.
Full-text available
In electronic nicotine delivery systems (ENDS), coil resistance is an important factor in the generation of heat energy used to change e-liquid into vapor. An accurate and unbiased method for testing coil resistance is vital for understanding its effect on emissions and reporting results that are comparable across different types and brands of ENDS and measured in different laboratories. This study proposes a robust, accurate and unbiased method for measuring coil resistance. An apparatus is used which mimics the geometric configuration and assembly of ENDS reservoirs, coils and power control units. The method is demonstrated on two commonly used ENDS devices—the ALTO by Vuse and JUUL. Analysis shows that the proposed method is stable and reliable. The two-wire configuration introduced a positive measurement bias of 0.086 (Ω), which is a significant error for sub-ohm coil designs. The four-wire configuration is far less prone to bias error and is recommended for universal adoption. We observed a significant difference in the coil resistance of 0.593 (Ω) (p < 0.001) between the two products tested. The mean resistance and standard deviation of the reservoir/coil assemblies was shown to be 1.031 (0.067) (Ω) for ALTO and 1.624 (0.033) (Ω) for JUUL. The variation in coil resistance between products and within products can have significant impacts on aerosol emissions.
Full-text available
Background Electronic nicotine delivery systems (ENDS; e-cigarettes), consisting of a battery, heating element and e-liquid, have evolved significantly with wide variation in design, components, operating powers, and chemical constituents. Generated aerosols have been reported to contain potentially toxic substances. We conducted a systematic review to assess what is known about the presence of toxicants in ENDS aerosols in order to inform how system design could mitigate risk. Methods Articles reporting on or evaluating design characteristics of ENDS and aerosol constituents were included and summarized. Results The search identified 2,305 articles, of which 92 were included after full-text review. Findings were grouped into 6 major categories of potentially harmful chemicals: carbonyls, volatile organic chemicals, trace elements, reactive oxygen species and free radicals, polycyclic aromatic hydrocarbons, and tobacco-specific nitrosamines. In general, higher concentrations of aerosol toxicants are associated with increased power or voltage. Aerosol toxicants are also associated with e-liquid flavoring agents existing as primary ingredients or as products of thermal degradation. Conclusions Improved ENDS design can reduce toxicant levels. Additional research is needed to develop a framework for optimizing system characteristics to minimize exposure, especially with respect to heating power and e-liquids. Both manufacturers and regulatory agencies have roles in reducing toxicants and potential health risks from ENDS.
Full-text available
Dangerous levels of harmful chemicals in electronic cigarette (e-cigarette) aerosols were reported by several studies, but variability in e-cigarette design and use patterns, and a rapid development of new devices, such as JUUL, hamper efforts to develop standardized testing protocols and understand health risks associated with e-cigarette use. In this study, we investigated the relative importance of e-cigarette design, power output, liquid composition, puff topography on e-cigarette emissions of carbonyl compounds, carbon monoxide (CO), and nicotine. Four popular e-cigarette devices representing the most common e-cigarette types (e.g., cig-a-like, top-coil, ‘mod’, and ‘pod’) were tested. Under the tested vaping conditions, a top-coil device generated the highest amounts of formaldehyde and CO. A ‘pod’ type device (i.e., JUUL) emitted the highest amounts of nicotine, while generating the lowest levels of carbonyl and CO as compared to other tested e-cigarettes. Emissions increased nearly linearly with puff duration, while puff flow had a relatively small effect. Flavored e-liquids generated more carbonyls and CO than unflavored liquids. Carbonyl concentrations and CO in e-cigarette aerosols were found to be well correlated. While e-cigarettes emitted generally less CO and carbonyls than conventional cigarettes, daily carbonyl exposures from e-cigarette use could still exceed acute exposure limits, with the top-coil device potentially posing more harm than conventional cigarettes.
Full-text available
This case series characterizes nicotine absorption among adults who regularly use a pod-based electronic nicotine delivery system.
Full-text available
Electronic cigarette uses propylene glycol and glycerol to deliver nicotine and flavors to the lungs. Given the hundreds of different brands, the thousands of flavors available and the variations in nicotine concentrations, it is likely that electronic cigarette settings and e-liquid composition affect the size distribution of particles emitted and ultimately pulmonary deposition. We used the inEx-pose e-cigarette extension to study two separate modes of operation of electronic cigarettes, namely power-controlled and the temperature-controlled. We also assessed several e-liquids based on propylene glycol and glycerol concentrations , nicotine content, and selected monomolecular flavoring agents (menthol, vanillin, and maltol). Particle size distribution was measured using a Condensation Particle Counter and a Scanning Mobility Particle Sizer spectrometer. Lung deposition was predicted using the International Commission on Radiological Protection model. For all resistance coils, increase in power delivery generated larger particles while maintaining a higher coil temperature generated smaller particles. Increase in glycerol concentration led to the generation of larger particles. With regard to flavors, we showed that despite minor effect of menthol and maltol, vanillin dramatically increased particle size. Presence of nicotine also increased particle size. Finally, particles emitted by the electronic cigarette were predicted to mainly deposit in the alveoli and conditions generating larger particle sizes led to a reduction in predicted lung deposition. This study shows that coil temperature, propylene glycol and glycerol concentrations, presence of nicotine, and flavors affect the size of particles emitted by an electronic cigarette , directly affecting predicted lung deposition of these particles.
E-cigarette aerosol is a complex mixture of gases and particles with a composition that is dependent on the e-liquid formulation, puffing regimen, and device operational parameters. This work investigated mainstream aerosols from a third generation device, as a function of coil temperature (315-510 °F, or 157-266 °C), puff duration (2-4 s), and the ratio of propylene glycol (PG) to vegetable glycerin (VG) in e-liquid (100:0-0:100). Targeted and untargeted analyses using liquid chromatography high-resolution mass spectrometry, gas chromatography, in situ chemical ionization mass spectrometry, and gravimetry were used for chemical characterizations. PG and VG were found to be the major constituents (>99%) in both phases of the aerosol. Most e-cigarette components were observed to be volatile or semivolatile under the conditions tested. PG was found almost entirely in the gas phase, while VG had a sizable particle component. Nicotine was only observed in the particle phase. The production of aerosol mass and carbonyl degradation products dramatically increased with higher coil temperature and puff duration, but decreased with increasing VG fraction in the e-liquid. An exception is acrolein, which increased with increasing VG. The formation of carbonyls was dominated by the heat-induced dehydration mechanism in the temperature range studied, yet radical reactions also played an important role. The findings from this study identified open questions regarding both pathways. The vaping process consumed PG significantly faster than VG under all tested conditions, suggesting that e-liquids become more enriched in VG and the exposure to acrolein significantly increases as vaping continues. It can be estimated that a 30:70 initial ratio of PG:VG in the e-liquid becomes almost entirely VG when 60-70% of e-liquid remains during the vaping process at 375 °F (191 °C). This work underscores the need for further research on the puffing lifecycle of e-cigarettes.
The aerosols generated from electronic cigarettes have a significant impact on the human respiratory system. Understanding the vaporization characteristics and aerosol optical properties of electronic cigarettes is important for assessing human exposure to aerosols. An experimental platform was designed and built to simulate the atomization process of electronic cigarette and detect the laser transmissivity of aerosols. The optical properties of single particles and polydispersed particle system for aerosols in the visible wavelength ranges of 400∼780 nm were analyzed based on Mie theory. The results show that a higher heating power supplied by coil results in a larger average vaporization rate of e-liquid. Meanwhile, the steady-state transmissivity of the laser beam for aerosols reduces as the heating power increases. Under the same heating power and puffing topography, the total particulate mass (TPM) of aerosols generated by the e-liquid composed of higher vegetable glycerin (VG) content decreases. The scattering efficiency factor of aerosol particle of electronic cigarette increases with an increase in particle size. The volume scattering coefficients of a polydispersed particle system of aerosols decrease as the incident visible wavelengths increase. A higher VG content in e-liquid results in decreased TPM and particle number concentration of aerosols and increased the volume scattering coefficient in the visible wavelength range. It can explain an interesting phenomenon that a lower TPM and a better visual effect brought by the aerosols generated by the e-liquid with a higher VG content could be observed concurrently. The mass indexes (e.g., TPM, average vaporization rate, average mass concentration) and optical indexes (e.g., volume scattering coefficient, laser transmissivity) are suggested to be used for the comprehensive evaluation of relative amounts of aerosols. The results have potential significances for the objective and quantitative assessments of aerosols generated from electronic cigarettes.
Recent reports have linked severe lung injuries and deaths to the use of e-cigarettes and vaping products. Nevertheless, the causal relationship between exposure to vaping emissions and the observed health outcomes remains to be elucidated. Through chemical and toxicological characterization of vaping emission products, this study demonstrates that during vaping processes, changes in chemical composition of several commonly used vape juice diluents (also known as cutting agents) lead to the formation of toxic byproducts, including quinones, carbonyls, esters and alkyl alcohols. The resulting vaping emission condensates cause inhibited cell proliferation and enhanced cytotoxicity in human airway epithelial cells. Notably, substantial formation of the duroquinone and durohydroquinone redox couple was observed in the vaping emissions from vitamin E acetate, which may link to acute oxidative stress and lung injuries. These findings provide an improved molecular understanding and highlight the significant role of toxic byproducts in vaping-associated health effects.
An electronic cigarette (e-cig) generates aerosols by vaporizing the e-liquid, which mainly consists of propylene glycol (PG), vegetable glycerin (VG), and nicotine. Understanding the effects of e-liquid main compositions on e-cig aerosols is important for exposure assessment. This study investigated how the PG/VG ratio and nicotine content affect e-cig aerosol emissions and dynamics. A tank-based e-cig device with 10 different flavorless e-liquid mixtures (e.g., PG/VG ratios of 0/100, 10/90, 30/70, 50/50, and 100/0 with 0.0% or 2.4% nicotine) was used to puff aerosols into a 0.46 m³ stainless steel chamber for 0.5 h. Real-time measurements of particle number concentration (PNC), fine particulate matter (PM2.5), and particle size distributions were conducted continuously throughout the puffing and the following 2-h decay period. During the decay period, particle loss rates were determined by a first-order log-linear regression and used to calculate the emission factor. The addition of nicotine in the e-liquid significantly decreased the particle number emission factor by 33%. The PM2.5 emission factor significantly decreased with greater PG content in the e-liquid. For nicotine-free e-liquids, increasing the PG/VG ratio resulted in increased particle loss rates measured by PNC and PM2.5. This pattern was not observed with nicotine in the e-liquids. The particle loss rates, however, were significantly different with and without nicotine especially when the PG/VG ratios were greater than 30/70. Compared with nonvolatile di-ethyl-hexyl subacute (DEHS) aerosols, e-cig particle concentration decayed faster inside the chamber, presumably due to evaporation. These results have potential implications for assessing human exposure to e-cig aerosols. Copyright © 2020 American Association for Aerosol Research