Puffing Topography: A Tool to Evaluate Vaping Behavior and Exposure Risks

Abstract

The ever-changing popularity of electronic nicotine delivery systems (ENDS) among both youth and adults in the United States has been influential in shaping users’ perceptions and behaviors. This behavior driven ENDS usage is described as puffing topography (PT) which includes user’s puff duration, flow rate, intra puff interval, the volume of e-liquid used and total number of puffs per session. These metrics are not only useful for characterizing individual vaping behaviors but are also critical for assessing the extent of exposure to potentially harmful substances such as nicotine, volatile organic compounds (VOCs), and particulate matter (PM) emitted during use. Previous studies have indicated that puff volume and flow rate are distinct but related parameters that determine exposure to hazardous emissions among users and bystanders. However, current evidence suggests that vaping behavior is also influenced by the age at which users first encounter ENDS, the strength of the nicotine present, and whether users develop circadian patterns of ENDS usage. This review article, which is a part of the Special Issue Science Education and Research on Vaping and Interventions for Community Engagement summarizes the critical aspects of PT and explores how various factors including lifestyle, gender, e-liquid composition (such as flavor and nicotine concentration), and device parameters can influence exposure risks. The standardization of puffing topography as a tool to evaluate vaping behavior and exposure risks to toxic emissions could be instrumental in developing consensus standards for ENDS and protecting public health.

What is Puffing Topography: Understanding Vaping Behavior

Puffing Topography (PT) essentially describes users’ vaping behavior while utilizing ENDS products. In recent years, PT has emerged as a powerful tool to evaluate how vaping behavior influences exposure to potentially harmful constituents within vaping emissions and vaping related health outcomes [1]. Critical attributes of PT include puff duration, flow rate, intra puff interval and the puff volume. Additional considerations include the composition of e-liquids, how long the user holds the vapor in the oral cavity and lungs, size and composition of particle matter (PM), metals and volatile organic compounds (VOCs), and deposition rate within the airways [2, 3]. Importantly, evaluating how ENDS users utilize their devices within realistic scenarios is paramount to not only understanding exposure risks but also in efforts to develop and implement potential intervention strategies when appropriate.

Current Puffing Topography Standards and Assessment Tools

Accurate puffing topography assessment is crucial for toxicological research, regulatory evaluations, product design improvements, and understanding vaping behaviors. As ENDS have evolved, various tools have been developed to monitor and analyze puffing behaviors. These tools can be broadly categorized into laboratory-based simulators and portable monitoring devices, each offering unique capabilities for assessing user exposure, emission profiles, and topography patterns. While most tools share real-time measurement capabilities for puff volume, duration, and flow rate, they differ in accuracy, adaptability, portability, and emissions analysis [4, 5]. In an effort to standardize chemical testing and emissions profiling of various ENDS devices, puffing topography profiles have been developed and recommended by governing agencies. The ISO 20768:2018 standard, derived from the Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) Recommended Method No. 81 (CRM 81), provides a standardized puffing protocol for laboratory testing of ENDS aerosol emissions. This protocol specifies a square-wave puffing profile consisting of a 55 mL puff volume, 3-second duration, and 30-second interval collectively known as the 55/3/30 regimen and was originally designed to simulate the inhalation patterns of early-generation Mouth-to-Lung (MTL) ENDS devices under controlled laboratory conditions [6, 7]. In accordance with ISO 7210:2013, CRM 81 further prescribes a fixed flow rate of 18.3 mL/s and details associated calibration procedures. However, the method does not address aerosol collection or trapping and is limited to devices with coil resistances greater than 1 ohm, restricting its applicability for characterizing modern sub-ohm systems and Direct-to-Lung (DTL) inhalation styles [7, 8]. In contemporary laboratory research, both ISO and CORESTA protocols are valuable for ensuring inter-laboratory reproducibility and methodological standardization, growing concerns have emerged regarding their ability to accurately reflect current ENDS usage patterns. This is particularly relevant in the context of high-powered, modifiable devices with adjustable airflow, and the increasing prevalence of nicotine salt formulations, all of which significantly alter aerosol output and inhalation dynamics as shaped by user-specific puffing topography [7, 8]. Scientific literature and real-world puffing topography measurement demonstrate that user puffing behavior frequently diverges from standardized test conditions, with puff volumes often exceeding 100 mL and durations extending to 3–4 seconds [4–6]. These behavioral deviations are influenced by factors such as device wattage, coil configuration, user demographics, and e-liquid composition, resulting in substantial variability in ENDS emission exposure [9–11].

Considering the discrepancy between CRM 81 recommendations and actual ENDS usage, this standard alone is inadequate for comprehensive exposure and risk assessment. To improve ecological validity, it should be supplemented with empirical PT data obtained through portable topography monitors (discussed below) or human-subject testing conducted under naturalistic conditions [6–8, 10]. Integrating such data is essential for aligning emissions and exposure science with actual usage patterns. Considering that ENDS use is highly variable—shaped by behavioral, biological, and product-specific factors robust and representative assessment of puffing behavior is critical to support accurate toxicological risk assessment and inform the development of performance-based regulatory frameworks.

There are a variety of portable puffing topography devices commercially available such as the SA7, SPA/m, and CReSS Pocket & CreSSmicro, which are designed for real-world vaping behavior monitoring. The SA7 is optimized for ENDS puffing analysis, featuring relocated pressure tubes to minimize aerosol condensation, a removable cap for maintenance, and a spigot to reduce jetting effects [12, 13]. This tool provides moderate accuracy, measuring puff volumes within 5 mL of preset values, making it a reliable tool for vaping behavior studies. The SPA/m offers a higher level of adaptability, accommodating various e-cigarette shapes and mouth-end designs, while maintaining ±10% accuracy in puff volume measurement [14, 15]. An additional feature includes a broad measurement range of operation, capturing puff volumes from 20–100 mL and durations between 1–9.9 seconds, making it well-suited for topography-based research. However, challenges exist when determining multi-peak puff detection, which requires careful calibration and data interpretation [15].

Among portable puffing topography devices, the CReSS Pocket and CReSSmicro are specifically designed for individual vaping behavior tracking. These devices collect puff volume, flow rate, peak flow, inter-puff interval, puff duration, and time to peak, enabling researchers to assess real-world user behavior [15]. While they offer convenient data collection, their accuracy varies depending on puff parameters, often underestimating puff duration at higher flow rates [16]. Additionally, the mouthpiece attachment may influence natural puffing behaviors, necessitating our research center to specific adjustments to maintain data integrity [1, 5]. Despite some limitations, CReSS devices remain valuable in clinical studies by supporting standardized vaping topography protocols. Although portable PT tools provide insights into naturalistic puffing behavior, they may require calibration and can influence puffing patterns due to mouthpiece or sensor design.

Similarly, PuffPacket has been introduced to monitor ENDS usage patterns in real-world settings, incorporating geolocation to track users’ movement and context. A smartphone-based app connects via Bluetooth to a compact hardware attachment that detects electrical signals generated during each puff, enabling accurate identification of puff events without altering ENDS operation. The system also logs contextual data such as time, location, total puff count, user activity, and puffing intervals, offering a detailed view of individual vaping behavior. Validation through laboratory and field studies has demonstrated that PuffPacket reliably captures fine-grained puffing patterns across various ENDS models. By overcoming the limitations of self-reporting and manual tracking, the platform supports large-scale, objective, and longitudinal research, providing valuable data for public health studies, nicotine exposure assessment, and intervention development [17].

The Wireless Personal Use Monitor (wPUM) is a pressure-based puffing topography assessment tool that monitors airflow through an orifice plate. As air passes through the plate, it generates a pressure differential across a sensor, which is then converted into an analog voltage by a transducer. This signal is digitized at a sampling rate of 40 samples/ second using an analog-to-digital converter. The high-resolution digital signal enables precise recording of puffing behavior, capturing fine temporal details such as puff timing, frequency, and duration, along with date and time of use. The system can store usage data for up to one month. In addition, the second-generation wPUM devices have been characterized and validated for accurate measurement of inhalation topography [18, 19].

As an alternative to external sensor modifications, puff-counter ENDS devices are inherently designed to capture puffing topography profiles. Yingst et al. employed these devices to evaluate whether self-reported ENDS use frequency, as measured by the Penn State Electronic Cigarette Dependence Index (PSECDI), aligns with real-time, device-recorded usage. Participants in this study were instructed to press the device button and inhale simultaneously, with a puff automatically logged each time the button was held for at least one second to prevent accidental counts. They used the device throughout the day and recorded the daily puff total, shown on the counter (which reset at each recharge), in a diary. During follow-up visits, a 7-day timeline follow-back was completed using the diary, and the mean daily puff count was calculated from the recorded data. This study found that self-reported “times per day” from the PSECDI significantly predicted the actual number of ENDS puffs taken. While self-reported frequency of use appears to be a reliable indicator of overall usage, accurately quantifying ENDS consumption patterns remains challenging [20].

Collectively, selecting appropriate puffing topography tools and ensuring their compatibility with ENDS aerosol generation and characterization methods (discussed in [21]) should be guided by the study’s objectives and any experimental limitation. Conversely, portable devices such as SA7, SPA/m, and CReSS models offer behavioral insights but require frequent calibration to ensure accuracy. As vaping research advances, the integration of topography tools with emissions analysis techniques will be critical in improving comparability across studies, regulatory decision-making, and public health assessments.

Trends and Risk Factors Influencing Vaping Behavior

ENDS devices have garnered considerable attention among US adults, driven by the misconception that aerosols produced by ENDS are less harmful than traditional smoking. Surveillance and behavioral data collected by the Behavioral Risk Factor Surveillance System (BRFSS) and National Health Interview Survey (NHIS) suggest prevalence of ENDS use remains greater than 3% [22–24]. This shift significantly correlates with habituation and dependency among adults (21–24 years), and students, suggesting nicotine dependency [23, 24]. Furthermore, adolescents who were exposed to ENDS early in life tend to continue as young adults [22, 25][4, 7]. Various studies have utilized puffing topography to understand vaping behavior and nicotine dependency. For example, Lee et al. evaluated puff topography from established and non-established ENDS users over a period of 1 week. Larger puff volume per session and longer puff durations remained a key hallmark for established users as compared to the non-established ENDS users[3]. While circadian puffing behavior analysis by Kosmider et al., over 24 hours showed that certain ENDS users consume 156.2±10.3 puffs, 10.2±7.9 puffs per session, with an puffing interval of 15.4±22.0 sec, single puff lasting 3.0±1.2 sec, puff volume 73.4±51.5 ml and flow rate of 24.7±10.2 ml/sec. Within this study, puff intake peaked at 11:00 am (14.4±14.9 puff), for those who woke up early in the morning or for persons using their device for the first time of the day. While a second peak was observed at 6:00 pm (13.1±3.4 puffs) [26]. This evidence further suggests that user preference and lifestyles drive differences in vaping behavior, including the difference of behavior on weekdays versus weekend routines meaningfully shape vaping behavior, including puff frequency, duration, and intensity [27]. These behavioral patterns introduce variability that challenges the assumptions of standardized emissions testing and underscore the need for complementary exposure assessment tools. Puffing topography, in this context, holds considerable promise as a potential benchmark methodology, offering a structured, evidence-based means to quantify inhalation behavior and inform regulatory evaluations of ENDS products [3, 28]. By systematically quantifying inhalation parameters such as puff volume, duration, inter-puff interval, and flow rate puffing topography enables precise characterization of user exposure profiles and emission dynamics. Empirical evidence consistently demonstrates that elevated puff volumes and flow rates are directly associated with increased emissions of PM, VOCs, and metals, which collectively enhance toxicological burden via elevated deposition in the tracheobronchial and alveolar regions of the respiratory tract [1, 3–5, 28, 29]. Computational modeling and chamber-based studies corroborate these findings, underscoring the importance of incorporating user-specific inhalation profiles into exposure assessment paradigms [1, 4, 5, 29, 30].

Standardized PT protocols ranging from CORESTA-81, 55 mL/3 s regimen to University of Maryland Baltimore’s 75 mL/2.5 s approach have been adopted for emissions testing. However, substantial inter-study variability in puffing behavior highlights the need for harmonized reference standards that reflect real-world use patterns and permit cross-platform comparison of harmful and potentially harmful constituents (HPHCs) [6, 8, 31]. Portable devices such as the CReSS Pocket, SPA/m, and SA7 systems have facilitated in situ characterization of puffing behavior, enabling the integration of naturalistic usage metrics into toxicological evaluations, emissions modeling frameworks, and Premarket Tobacco Product Application (PMTA) submissions. The PMTA pathway, mandated by the FDA, applies to all tobacco products, including ENDS, and requires manufacturers to demonstrate that their products are appropriate for the protection of public health. By incorporating real-world puffing behavior, these devices enhance the scientific rigor of regulatory assessments, ensuring that emissions and exposure evaluations accurately reflect consumer usage patterns [4, 31].

From a regulatory standpoint, PT offers substantial utility across the premarket and postmarket continuum. In premarket applications, PT data can be leveraged to align machine-generated emissions testing with actual consumer use conditions, enhancing ecological validity and improving FDA evaluation fidelity [32–34]. In postmarket contexts, PT-enabled surveillance can be used to identify high-risk behaviors (e.g., cloud chasing, dual product use) and population-level exposure trends, supporting timely regulatory interventions and product performance monitoring [35, 36]. Furthermore, integration of PT data into labeling and product design guidelines could inform consumer-facing disclosures about nicotine delivery kinetics and potential health impacts under varying inhalation intensities.

Importantly, PT also provides a critical lens for investigating product-specific variability including effects of coil aging, device power modulation, and e-liquid formulation, which significantly influence aerosol physicochemical properties and associated health risks [1, 4, 5, 29, 33]. As ENDS technologies continue to evolve, particularly in the domains of nicotine salt formulations and high-nicotine disposables, PT offers a scalable and adaPTive tool for ensuring regulatory standards remain aligned with current use patterns and emerging product architectures.

In sum, PT serves as an indispensable bridge between user behavior, aerosol chemistry, and exposure science. Its integration into regulatory frameworks offers a path toward more nuanced, evidence-driven risk assessments, ultimately supporting the development of performance-based standards and targeted harm reduction strategies that account for the complex interplay of behavioral, technical, and toxicological factors in ENDS use.

Sex and Gender Effects on Vaping Behavior

Perception of tobacco products among males and females differs significantly. Young males are more prone to experimenting with vaping than females [37]. While experienced males prioritize the nicotine rush, females lean towards flavor and other aesthetic aspects and often perceiving ENDS as harmless to others [38]. Males typically seek higher nicotine concentrations, larger, stylish tanks, often under the misconception that e-cigarettes are less harmful than traditional cigarettes. Beyond gender disparities, hormonal differences such as estrogen significantly impact nicotine metabolism, aiding females in quitting or reducing dependence on ENDS, as compared to males [39, 40]. Moreover, the continuation of ENDS usage has been shown to increase the risk of respiratory disorders, lung cancer, and related ailments [40]. Cross-sectional studies by El-Shahawy et al. and Erhabor et al. indicate that males living in the southern and western parts of the United States, as well as those identifying as lesbian, gay, bisexual, or transgender living in rural areas, exhibit higher dependency on e-cigarettes [41, 42].

Gender differences in e-cigarette use are influenced by a combination of biological and behavioral factors, for example males tend to take larger puff volumes [43], while females often take longer, slower and more puffs, particularly when transitioning from conventional cigarettes [44] or vaping episodes [45]. This variation is attributed to higher and faster nicotine metabolism in as females, as they metabolize nicotine and cotinine more rapidly due to estrogen, potentially leading to more frequent puffing to maintain nicotine levels [46, 47]. Males on the other hand are generally more sensitive to nicotine-rewarding effects, whereas females experience greater adverse subjective sensitivity, which may contribute to differences in puff volume. Non-pharmacological factors also play a role, with females showing heightened sensitivity to visual and olfactory cues, leading them to take smaller, more frequent puffs to enhance sensory experiences [48]. Flavor and device preferences further shape puffing behavior, as females tend to favor sweet flavors, use lower nicotine concentrations, and prefer disposable or first-generation devices, which may influence airflow and puff characteristics. Health outcomes also differ, with female smokers reporting more respiratory symptoms and lower overall health ratings, potentially resulting in smaller puff volumes to minimize discomfort [43, 48]. Contrary to these findings, Blank et al, concluded that gender difference do not contribute to puff volume [49].

Additionally, during the COVID-19 pandemic, female secondary school students reported taking more puffs per vaping session compared to their male counterparts [50]. In a different study, it was found that the use of ENDS decreased among 13–18-year-olds in Iceland; however, this decline was linked to a significant rise in mental health, and emotional dependence issues among adolescents, particularly among girls. Moreover, authors noted no significant variation in vaping sessions per day, however, females tended to take more puffs per session [52].

Apart from gender, perception of ENDS along with biological and physiological factors varies among males and females. Males are influenced by real world social factors such as peer pressure to vape, among cigarette users, while females are influenced by social media contents, family or friend’s recommendations and preferred vape pen devices [53]. Furthermore, males perceive ENDS “less harmful than cigarettes” while females see their habits as “less harmful to others”, which drives ENDS usage [54]. Characteristically, females prefer to use disposable, non-tobacco flavors, with less to lower nicotine, and probably elegant looking ENDS [43, 53].

Much of the current understanding of gender-based differences in puffing behavior is derived from research on traditional cigarette smoking, largely because combustible cigarettes have been used and studied extensively for decades, whereas e-cigarettes are relatively recent in their introduction. Males generally have larger lungs and airways, which supports higher puff volumes, while females tend to take a greater number of shorter puffs due to smaller lung capacity. Men typically use more abdominal musculature during inhalation, whereas women rely more on thoracic breathing, which may result in a higher concentration of smoke exposure per unit area despite lower puff volumes [55, 56]. While these insights were established using combustible tobacco products, they may offer translatable implications for ENDS aerosol exposure, particularly as e-cigarette aerosols also consist of respirable particulates. However, differences in aerosol composition, temperature, and puff dynamics between cigarettes and ENDS highlight the need for dedicated research to confirm whether these physiological patterns similarly influence vaping-related exposure. Further this behavior by females is also facilitated by increased rate of nicotine metabolism though various hormones and may contribute to lung disease [56]. Lower level of estradiol or progesterone has been shown to decrease puff intensity. Decreased progesterone to estradiol ratio contributes to variable puff intake and increased smoking. While higher progesterone relative to estradiol prevents reactivity against nicotine. Contrary to this, increased estradiol during menstruation cycle at follicular stage results in increased puff, and sensitivity to nicotine, while at luteal phase increase nicotine sensitivity. Mechanistically, estradiol promote vulnerability among females through activation of dopaminergic rewards pathway, while progesterone prevents this activation [57–59]. Suggesting that gender-based distinctions underscore the complexity of e-cigarette use patterns and other factors such as device type, nicotine concentration, and user experience also play significant roles in determining puff volume and overall vaping behavior, highlighting the need for targeted research and harm reduction strategies.

How ENDS Device Type and E-liquid Influence Vaping Behavior

Puffing topography also varies depending upon composition of e-liquid, nicotine content and device type (variable versus constant power output). For example, ENDS users trying alternative devices for the first time, altered their puffing behavior by using higher puff number, lower inter-puff intervals, and increased duration of puffing to achieve nicotine yield/satisfactions [60–63]. Studies have shown that increased puff volume, and puff duration is associated with decreased concentration of nicotine and PG/G (Propylene glycol (PG) and glycerin (G)) concentration in e-liquids [64–66]. One study found use of ENDS with higher battery powers resulted in increases nicotine concentrations in plasma serum compared to users with lower battery powered devices [60–63]. Furthermore, studies indicate that ENDS users who transition from traditional cigarettes to ENDS significantly associate users’ satisfaction as a key parameter, which therefore influences ENDS puff topography and usages. Puff topography analysis revealed user satisfaction after transitioning to ENDS was achieved by larger, longer and more frequent puffs, with high flow rate resulting in generation of emissions including metals, VOCs and PM with known and unknown health concerns [27, 67, 68].

Role of Puffing Topography in Assessing Exposure Risks

Puffing behavior stands out as a consistent trait shared by both traditional cigarette smoker and ENDS users. Mouth-to-lung (MTL) puff behavior by traditional smoker draw smoke into their mouths before inhaling into their lungs. In contrast, certain ENDS users inhale emissions direct-to-lung (DTL). Because of this, ENDS accumulate higher cloud density, resulting in large, exhaled clouds, and a notable increase in puff flow rate (166.7 mL/s), which significantly influences particle emission rates. Particulate deposition by ENDS-DTL behavior strongly correlates with puff volume, duration, flow rate and lung injury [69, 70]. Moreover, extending the puff duration further leads to a notable elevation in coil temperature (20–50 °C/s), consequently causing an increase in the concentration of particles [71–73].

Exposure to ENDS aerosols, particularly in DTL vaping, has been associated with transitory lung inflammation and impaired gas exchange. Acute inhalation of aerosols from PG/VG e-liquids infused with or without nicotine and flavor at high power settings leads to airway epithelial injury and a sustained decline in oxygen levels, including reduced transcutaneous and arterial oxygen tension [74]. Studies using modeling tools such as the Multiple-Path Particle Dosimetry (MPPD) model, based on emissions from smoking machines, show that aerosol retention varies by e-liquid type and device setting. For instance, Ranpara et al. demonstrated that Vitamin E acetate (VEA), coconut oil, and medium-chain triglycerides produce aerosols that predominantly deposit in the tracheobronchial and pulmonary regions—sites consistent with injury observed in EVALI cases. Regional lung comparisons reveal greater particulate deposition in the right and lower lobes [75]. Additional studies confirm that ultrafine particles (MMAD 0.2–1.2 μm) can penetrate deep into the lungs, with total lung deposition ranging from 10%–45%, and up to 80% for ultrafine particles [76] [77].The regional comparison showed that this deposition was largely in the tracheobronchial and bronchoalveolar regions, with deposition fractions being 0.504–0.541 and 0.073–0.306, respectively [78]. MPPD modeling using human-generated aerosol profiles further supports enhanced deep-lung deposition of fine particulates [1]. Puffing behavior significantly influences this retention: larger puff volumes and durations increase both particle concentration and size [1] [78]. Device power, e-liquid composition, and flow rate further shape aerosol mass, geometry, and distribution [4, 78, 79].

Finally, user inhalation behaviors particularly puff depth, rate, and breath-holding play a critical role in determining where and how particles deposit within the lungs. Slow, deep inhalation and prolonged breath-holding enhance diffusion-driven particle transport into small airways and alveoli [86]. As shown by Jeon et al. and Ranpara et al., these behaviors significantly modulate particle size distribution and retention, underscoring their role in shaping individual exposure and pulmonary risk. Suggesting that puffing behavior is a key driver of aerosol deposition in ENDS use, with higher volumes promoting deeper penetration of fine and ultrafine particles into the tracheobronchial and alveolar regions. This increases the risk of epithelial injury, impaired gas exchange, and inflammation [1, 29, 75]. However, its effects are highly context-dependent shaped by device power, flow rate, aerosol volatility, and user behavior. The non-linear relationship between puff volume and particulate characteristics challenges assumptions of dose-response proportionality and highlights the need for behavior-informed exposure models in risk assessment.

Supporting this view, an NIH-funded study, along with additional research conducted at the Chemical Insights Research Institute of UL Research Institutes (CIRI-ULRI) under IRB Protocol No. H22081, demonstrates that puffing topography is a key determinant of ENDS aerosol emissions and user-specific exposure [1, 4, 29, 87]. Puffing behavior was measured using the CReSS Pocket device (limitation and advantages discussed earlier) while participants used their personal ENDS devices, capturing puff volume, duration, flow rate, inter-puff interval, and peak inhalation flow. Users were stratified into low (<90 mL/puff), moderate (90–150 mL/puff), and high (>150 mL/puff) volume groups. These patterns were independent of device type, nicotine content (3–5%), e-liquid flavor, or user demographics, underscoring the behavioral variability among ENDS users. Individualized puffing profiles were replicated using a programmable ENDS Aerosol Generation System (EAGS)[4], which operated each user’s device under their specific topography in a temperature- and humidity-controlled 6 m³ stainless steel chamber with real-time aerosol monitoring.

Higher puff volumes produced increased levels of fine and ultrafine particulate matter and elevated concentrations of toxic metals, including vanadium, cobalt, and lead. These metals, detected in the aerosol phase, are associated with oxidative stress, inflammation, and systemic toxicity. In addition, volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylene classified as respiratory irritants and carcinogens were more abundant in emissions from high-volume users. These differences were attributable to puffing behavior rather than device brand or format. Use of personal devices improved ecological validity by accounting for coil resistance, power variability, and airflow configuration that influence aerosol generation. This behaviorally anchored approach links inhalation patterns with toxicant yield, supporting risk stratification based on puff intensity. These findings emphasize the need to incorporate user-specific puffing profiles into regulatory testing and exposure models. Standardized protocols that ignore behavioral variability risk underestimating exposures, particularly in high-intensity users. Integrating real-world topography is essential for accurate risk assessment and the development of evidence-based regulatory policy.

Beyond behavioral patterns, the relationship between puff volume and particulate matter (PM) characteristics in ENDS emissions can be complex. It is shaped by a range of interacting variables, including power settings, puff volume and duration, flow rate, and aerosol dynamics. For instance, a modifiable ENDS at higher power levels (7.5 W), increasing puff volume from 55 mL to 75 mL resulted in a reduction in particle size, and Mass Median Aerodynamic Diameter (MMAD) from 1.23 μm to 1.02 μm [88]. This suggests that higher puff volumes may alter the particle size distribution, depending on device settings. The length of a puff has also been shown to significantly influence aerosol output, as longer durations activate the atomizer for extended periods. Studies report a positive correlation between puff length and both particle number and concentration [89, 90]. Similarly, longer puff durations have been shown to significantly increase aerosol output due to extended atomizer activation, with studies reporting a positive correlation between puff duration and particle number concentration [91–93]. These findings suggest that while puff volume may affect the physical attributes of emitted particles, the duration of inhalation plays a more direct role in determining total aerosol production and user exposure.

Flow rate and e-liquid composition also contribute to variations in emission profiles and influence the particle size and distribution of mainstream aerosols [69, 94, 95]. Notably, the combination of high puff volume and elevated power settings can further reduce aerosol size by limiting the time available for particle collision and coagulation, illustrating the nonlinear and dynamic nature of PM formation in e-cigarette emissions [69]. Additionally, e-cigarette aerosol particles are highly volatile, with particle number concentrations typically returning to background levels within 10–15 seconds after vaping regardless of ventilation conditions [88, 94, 95]. This highlights the transient nature of PM in ENDS emissions, distinguishing them from traditional tobacco smoke, which exhibits longer particle suspension times.

Collectively, ENDS users, particularly among youth and young adults, is sustained by behavioral factors and misconceptions about harm. However, aerosol emissions are highly variable and influenced by interacting parameters such as puff duration, volume, power settings, device type (device generation, customizable options) and flow rate. These factors collectively shape particle size, concentration, and volatility, highlighting the need for standardized methodologies to accurately assess exposure risk.

Conclusion

The systematic characterization of puffing topography represents a pivotal advancement in the assessment of ENDS-related exposure and health risk. This review underscores that user-specific inhalation dynamics encompassing puff duration, flow rate, volume, and inter-puff intervals serve as critical determinants of aerosol generation and toxicant delivery. These behavioral variables interact with device configuration, power output, and e-liquid composition to modulate aerosol physicochemical properties, including particle size distribution, metal content, and VOC concentrations. Importantly, empirical evidence demonstrates that high-intensity puffing behaviors particularly among youth and high-dependence users are associated with elevated emission profiles and enhanced deep-lung deposition, implicating these patterns in the pathophysiology of conditions such as EVALI. Portable and laboratory-based instrumentation, including CReSSmicro, SA7, SPA/m, PuffPacket, and wPUM, has enabled high-resolution profiling of individual vaping topography in both controlled and ecological settings, advancing the precision of exposure assessment models. These insights advocate for the integration of topography-informed metrics into regulatory science to refine emission testing protocols, establish behaviorally relevant exposure thresholds, and support targeted public health interventions. Leveraging puffing topography in this context provides a robust, evidence-based foundation for policy development aimed at mitigating harm, particularly in vulnerable subpopulations. As ENDS technologies continue to evolve, embedding real-world vaping behavior into surveillance and regulation will be essential for safeguarding public health with scientific rigor.

Data Availability Statement.

Data sharing is not applicable to this article as no new data were created or analyzed in this study.