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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2021)

In recent years, electronic cigarettes (e-cigs) have gained increasing popularity among adolescents and young adults while emerging data raise concerns about their health effects. Essentially different from conventional tobacco cigarettes (t-cigs), e-cigs produce an aerosol via vaporization of the e-liquid, which is typically made of propylene glycol (PG), vegetable glycerin (VG), nicotine, water, and flavoring compounds. E-cig aerosols mainly consisting of liquid droplets were found highly dynamic and volatile. However, knowledge on the transport and transformation of e-cig aerosols and the related exposure is still limited. This dissertation investigated the characteristics of e-cig aerosols and evaluated the impacts of e-cig use on indoor air quality focusing on the effects of e-liquid and environmental factors. This work is subdivided into the following seven chapters: an overview (Chapter 1), a literature review (Chapter 2), three chapters of original research (Chapters 3-5), the conclusions of the work (Chapter 6). We first conducted a literature review to summarize the effects of e-cigs on indoor particulate matter (PM) pollution, chemical compositions of e-cig aerosols, and associated respiratory and cardiovascular effects. Many studies have reported high levels of ultrafine particles (UFPs, particles with an aerodynamic diameter ≤ 100 nm) and PM2.5 (particles with an aerodynamic diameter ≤ 2.5 μm) due to e-cig use (i.e., vaping) indoors, which were comparable to t-cig smoke. Although the concentrations of toxic chemical compounds in e-cig aerosols are generally lower than those in t-cig smoke, a substantial amount of vaporized PG, VG, nicotine, and hazardous substances, such as aldehydes and heavy metals, has been reported. Evidence confirms that e-cig use impairs indoor air quality and poses bystanders for risk of secondhand exposure. To explore the effects of e-liquid compositions on the e-cig aerosols, we investigated how PG/VG ratio and nicotine content affect e-cig aerosol emissions and dynamics. We found that adding nicotine to the e-liquid altered the particle emission factors. For nicotine-free e-liquids, increasing the PG/VG ratio resulted in increased particle loss rates measured by particle number concentration (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. In real-world settings, we assessed the impacts of e-cig use on indoor air quality in vape shops and their neighboring indoor spaces in multiunit buildings. The mean (SD) PNC and PM2.5 concentration in the studied vape shops were 2.8�10^4 (2.3�10^4) particles/cm3 and 276 (546) �g/m^3. Out of the six studied pairs, PNCs in five vape shops and PM2.5 in two vape shops were significantly correlated with those in their neighboring businesses. Nicotine was detected in the air of all the studied vape shops [mean (SD) 2.59 (1.02) �g/m^3] and neighboring businesses [mean (SD) 0.17 (0.13) �g/m^3]. We also identified major factors such as dilution, ventilation, and vaping density (puffs/h/100m^3) that influenced the behaviors of exhaled e-cig aerosols, and evaluated the transport of exhaled e-cig particles from the vape shop to its outdoor environment. Compared to mainstream e-cig aerosols measured in laboratory chamber studies, larger particle sizes (mode ~ 250 nm) were observed at the end of vaping in vape shops. We developed a ventilated artificial lung system to better understand how the human lung environment alters the inhaled e-cig aerosols. We used this system to assess the effects of breathing, temperature, and relative humidity (RH) on characteristics of inhaled e-cig aerosols in the last Chapter. Increasing the respiratory rate (from 10 to 15 BPM) and breath volume (from 480 to 720 ml) resulted in enhanced particle decay rates from 32 to 80 h^-1 in the ambient room environment. The decay rates under all breathing patterns increased by ~ 11 – 20% when changing the temperature and RH from ambient room to simulated lung conditions. The warm and humid lung environment resulted in hygroscopic growth of inhaled particles that significantly enhanced the presence of supermicron (> 1 �m) e-cig particles. Overall, the use of e-cigs that leads to high levels of PM2.5, UFPs, and gas-phase nicotine degrade the indoor air quality, raising concerns regarding secondhand exposure to e-cig aerosols. E-cig aerosols that are highly dynamic in the environment, especially small particles, can travel farther away and penetrate into neighboring indoor spaces. The characteristics of e-cig aerosols and related exposures can be affected by a wide range of factors including, but not limited to, e-liquid compositions, air exchange rate, ventilation, dilution, vaping density (puffs/h/100m^3), distance, inhalation and exhalation process in the human lung, and environmental conditions with varying temperature and humidity. These data can guide exposure assessment and mitigation strategies.

    Cover page: Characteristics of Electronic Cigarette Aerosol and Its Impact on Indoor Air Quality
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2020)
    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 diethyl-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.
    • 1 supplemental ZIP
    Cover page: Effects of propylene glycol, vegetable glycerin, and nicotine on emissions and dynamics of electronic cigarette aerosols
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2020)
    With the rapid increase in electronic cigarette (e-cig) users worldwide, secondhand exposure to e-cig aerosols has become a serious public health concern. We summarize the evidence on the effects of e-cigs on indoor air quality, chemical compositions of mainstream and secondhand e-cig aerosols, and associated respiratory and cardiovascular effects. The use of e-cigs in indoor environments leads to high levels of fine and ultrafine particles similar to tobacco cigarettes (t-cigs). Concentrations of chemical compounds in e-cig aerosols are generally lower than those in t-cig smoke, but a substantial amount of vaporized propylene glycol, vegetable glycerin, nicotine, and toxic substances, such as aldehydes and heavy metals, has been reported. Exposures to mainstream e-cig aerosols have biologic effects but only limited evidence shows adverse respiratory and cardiovascular effects in humans. Long-term studies are needed to better understand the dosimetry and health effects of exposures to secondhand e-cig aerosols.
      Cover page: Effects of Electronic Cigarettes on Indoor Air Quality and Health
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2022)
      The past decade marked a drastic increase in the usage of electronic cigarettes. The adverse health impact of secondhand exposure due to exhaled e-cig particles has raised significant concerns, demanding further research on the characteristics of these particles. In this work, we report direct volatility measurements on exhaled e-cig aerosols using a field-portable device (termed c-Air) enabled by deep learning and lens-free holographic microscopy; for this analysis, we performed a series of field experiments in a vape shop where customers used/vaped their e-cig products. During four days of experiments, we periodically sampled the indoor air with intervals of ~ 16 min and collected the exhaled particles with c-Air. Time-lapse inline holograms of the collected particles were recorded by c-Air and reconstructed using a convolutional neural network yielding phase-recovered microscopic images of the particles. Volumetric decay of individual particles due to evaporation was used as an indicator of the volatility of each aerosol. Volatility dynamics quantified through c-Air experiments showed that indoor vaping increased the percentage of volatile and semi-volatile particles in air. The reported methodology and findings can guide further studies on volatility characterization of indoor e-cig emissions.
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2021)
        Various volatile aerosols have been associated with adverse health effects; however, characterization of these aerosols is challenging due to their dynamic nature. Here, we present a method that directly measures the volatility of particulate matter (PM) using computational microscopy and deep learning. This method was applied to aerosols generated by electronic cigarettes (e-cigs), which vaporize a liquid mixture (e-liquid) that mainly consists of propylene glycol (PG), vegetable glycerin (VG), nicotine, and flavoring compounds. E-cig-generated aerosols were recorded by a field-portable computational microscope, using an impaction-based air sampler. A lensless digital holographic microscope inside this mobile device continuously records the inline holograms of the collected particles. A deep learning-based algorithm is used to automatically reconstruct the microscopic images of e-cig-generated particles from their holograms and rapidly quantify their volatility. To evaluate the effects of e-liquid composition on aerosol dynamics, we measured the volatility of the particles generated by flavorless, nicotine-free e-liquids with various PG/VG volumetric ratios, revealing a negative correlation between the particles' volatility and the volumetric ratio of VG in the e-liquid. For a given PG/VG composition, the addition of nicotine dominated the evaporation dynamics of the e-cig aerosol and the aforementioned negative correlation was no longer observed. We also revealed that flavoring additives in e-liquids significantly decrease the volatility of e-cig aerosol. The presented holographic volatility measurement technique and the associated mobile device might provide new insights on the volatility of e-cig-generated particles and can be applied to characterize various volatile PM.
          Cover page: Dynamic Imaging and Characterization of Volatile Aerosols in E‑Cigarette Emissions Using Deep Learning-Based Holographic Microscopy
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2021)
          With the rapid growth of the electronic cigarette (e-cig) market, there is an increasing number of vape shops that exclusively sell e-cigs. The use of e-cigs in the vape shop is a primary source of indoor particles, which might transport to its nearby indoor spaces in the multiunit setting. In this study, six pairs of vape shops and neighboring businesses in Southern California were recruited for real-time measurements of particulate pollutants between February 2017 and October 2019. The mean (SD) particle number concentration (PNC) and PM2.5 concentration in the studied vape shops were 2.8 × 104 (2.3 × 104) particles/cm3 and 276 (546) μg/m3, which were substantially higher than those in neighboring businesses and outdoor areas. In addition, 24-h time-weighted average (TWA) nicotine sampling was conducted in the six pairs and three additional pairs. Nicotine was detected in the air of all the studied vape shops and neighboring businesses, in which the mean (SD) concentration was 2.59 (1.02) and 0.17 (0.13) μg/m3, respectively. Inside vape shops, the dilution-corrected vaping density (puffs/h/100 m3) is a strong predictor of the particle concentration, and nicotine concentration highly depends on the air exchange rate (AER). Out of the six studied pairs, PNCs in five vape shops and PM2.5 in two vape shops were significantly correlated with those in their neighboring businesses. This correlation was stronger when the door of the vape shop was closed. When the door was open, environmental electronic vaping (EEV) aerosols, especially smaller particles, could transport from the vape shop to the outdoor environment. Overall, e-cig usage in the vape shop impacts both its own and nearby air quality, raising concerns regarding the risk of exposure to EEV aerosols in the surrounding environments.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2021)
            Electronic cigarette (e-cigarette) use has been linked to recent acute lung injury case clusters in over 2000 patients and dozens of deaths in the United States, however, the mechanism leading to lung injury is not certain although ultrafine particles, heavy metals, volatile organic compounds, and other harmful ingredients have been implicated. To systematically evaluate e-cigarette toxicity, we generated e-cigarette aerosols by varying the puff numbers (20-480), nicotine contents (0-24 mg/mL), and collected e-cigarette samples through an impinger system for biological assays. The calculated samples' concentration ranged from 1.96 to 47.06 mg/mL. THP-1 monocyte-differentiated macrophages, BEAS-2B bronchial epithelial cells, wild-type C57BL/6 mice, and NF-κB-luc transgenic mice were used to test the effects of these samples. E-cigarette samples showed cytotoxicity to THP-1 cells and BEAS-2B in vitro, leading to increased oxidative stress, inflammatory cytokine production with or without nicotine, and cell death. Furthermore, aerosol generated from PG is more toxic than VG. The toxicity of e-cigarette samples is at least partially due to the reactive oxygen species and aldehydes, which are generated during the aerosolization processes by the e-cigarette device. After NF-κB-luc mice exposed with e-cigarette samples by oropharyngeal aspiration, NF-κB expressions were observed in a dose-response fashion with or without nicotine. In addition, the e-cigarette samples induced neutrophil infiltration, IL-1β production, oxidative stress marker heme oxygenase-1 expression in wild-type C57BL/6 mice. These results suggested that oxidative stress, pro-inflammatory NF-κB pathway activation, and cell death are involved in e-cigarette aerosol-induced acute lung inflammation.
              Cover page: Electronic cigarette aerosols induce oxidative stress-dependent cell death and NF-κB mediated acute lung inflammation in mice
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2023)
              Electronic cigarettes (e-cigs) have become increasingly popular, especially among youth, raising concerns about their potential health risks. JUUL and Tank devices are two common types of e-cigs that deliver aerosols with varying nicotine levels and flavors. However, the differences in the aerosols generated from different devices and their corresponding cytotoxicity and pulmonary injury effects remain poorly understood. This study addresses these knowledge gaps by characterizing the aerosols of JUUL and Tank e-cig devices and testing their toxic effects on THP-1 and BEAS-2B human cell lines as well as the C57BL/6J mouse model. In our study, the lower-voltage device, the 3.7 V JUUL generates 2.72 mg/puff aerosols by using e-liquid containing 3% nicotine salt (i.e., nicotine benzoate), which is less than the 11.06 mg/puff aerosols generated by the 7.5 V Tank using e-liquid containing 2.4% freebase nicotine. Yet, the cytotoxicity results reveal that JUUL aerosols induced higher toxicity and increased production of pro-inflammation cytokines compared to Tank aerosols per puff. Additionally, we observed that JUUL induced more severe pulmonary inflammation and DNA damage compared to Tank after normalizing for cotinine, a nicotine metabolite, in vivo. Our findings suggest that the device design plays a more important role in e-cig aerosol-induced toxicity than the composition of the e-liquid or voltage. These results provide valuable insights into the health risks associated with various electronic-cig devices and offer an approach for evaluating them.
                Cover page: Differential Toxicity of Electronic Cigarette Aerosols Generated from Different Generations of Devices In Vitro and In VivoCreative Commons 'BY-NC-ND' version 4.0 license
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