Real-Time Measurement of Electronic Cigarette Aerosol Size Distribution and Metals Content Analysis

Abstract

Introduction: Electronic cigarette (e-cigarette) use is increasing worldwide and is highest among both daily and nondaily smokers. E-cigarettes are perceived as a healthier alternative to combustible tobacco products, but their health risk factors have not yet been established, and one of them is lack of data on aerosol size generated by e-cigarettes. Methods: We applied a real-time, high-resolution aerosol differential mobility spectrometer to monitor the evolution of aerosol size and concentration during puff development. Particles generated by e-cigarettes were immediately delivered for analysis with minimal dilution and therefore with minimal sample distortion, which is critically important given the highly dynamic aerosol/ vapor mixture inherent to e-cigarette emissions.Results: E-cigarette aerosols normally exhibit a bimodal particle size distribution: nanoparticles (11-25 nm count median diameter) and submicron particles (96-175 nm count median diameter). Each mode has comparable number concentrations (10 7 -10 8 particles/cm 3 ). "Dry puff" tests conducted with no e-cigarette liquid (e-liquid) present in the e-cigarette tank demonstrated that under these conditions only nanoparticles were generated. Analysis of the bulk aerosol collected on the filter showed that e-cigarette emissions contained a variety of metals.Conclusions: E-cigarette aerosol size distribution is different from that of combustible tobacco smoke. E-cigarettes generate high concentrations of nanoparticles and their chemical content requires further investigation. Despite the small mass of nanoparticles, their toxicological impact could be significant. Toxic chemicals that are attached to the small nanoparticles may have greater adverse health effects than when attached to larger submicron particles. Implications: The e-cigarette aerosol size distribution is different from that of combustible tobacco smoke and typically exhibits a bimodal behavior with comparable number concentrations of nanoparticles and submicron particles. While vaping the e-cigarette, along with submicron particles the user is also inhaling nano-aerosol that consists of nanoparticles with attached chemicals that has not been fully investigated. The presence of high concentrations of nanoparticles requires nanotoxicological consideration in order to assess the potential health impact of e-cigarettes. The toxicological impact of inhaled nanoparticles could be significant, though not necessarily similar to the biomarkers typical of combustible tobacco smoke.

A scattering methodology for droplet sizing of e-cigarette aerosols

“…As a result, the aerosol was drawn in the cylinder housing of the PDSP piston for a puff duration of 2 s. The aerosol was immediately exhausted from the PDSP housing by the action of the piston pushing off the aerosol for a duration of 1.4 s to two TSI aerosol diluters to recover 1/10 000 of the aerosol concentration and ensuring droplets could enter one by one into the LAS detector. Indeed, although the TSI diluter should minimize droplet evaporation, e-cigarette aerosol is generally highly volatile as highlighted in other work (Alderman at al., 2014;Ingebrethsen et al, 2012;Mikheev et al, 2016;Schripp et al, 2013) and may trigger droplet size change prior to a measurement is performed. Furthermore, use of the PDSP pump increased the aerosol residence time by at least 3.4 s prior to measurement.…”

Characteristics of secondhand electronic cigarette aerosols from active human use

“…Aldehydes (e.g., formaldehyde and acetaldehyde), which might be the product of the thermal dehydration of glycerin or glycols, have been detected in EC aerosols (McAuley et al 2012;Uchiyama et al 2013;Goniewicz et al 2014;Jensen et al 2015;Sleiman et al 2016). Compared with those in mainstream tobacco smoke, higher levels of nickel, chromium, and lead were also found in EC aerosols (Pellegrino et al 2012;Williams et al 2013;Lerner et al 2015;Mikheev et al 2016). Furthermore, studies have reported extremely high particle number concentrations (PNC) ranging from 7.69 £ 10 7 to 8.38 £ 10 9 particles/cm 3 in EC mainstream aerosols (Ingebrethsen et al 2012;Schripp et al 2013;Fuoco et al 2014;Mikheev et al 2016;Zhao et al 2016).…”

Electronic cigarettes—A review of the physiological health effects

“…"Direct dripping" is a popular method of vaping as it creates more aerosol, a stronger flavour, and a more potent "throat hit". This method potentially puts users at risk of exposing themselves to higher levels of toxicants and nanoparticles (Mikheev et al 2016;Talih et al 2016). Further studies, therefore, not only need to focus on EC aerosol composition but also on the power of the devices along with the modes of delivery by users.…”

“…These particles, and especially the smaller nanoparticles, can attach to chemicals found in the aerosol or in the EC liquid. This can potentially cause more damage than would otherwise occur as the particles can then settle in the lungs (Pellegrino et al 2012;Fuoco et al 2014;Marini et al 2014;Schober et al 2014;Manigrasso et al 2015;Trassierra et al 2015;Casanova-Cháfer et al 2016;Mikheev et al 2016). EC liquids with a high propylene glycol to glycerol ratio tend to produce smaller particles, and toxicants attached to these small particles are then more likely to reach alveoli and cause damage (Heyder 2004;Pellegrino et al 2012;Long 2014;Schober et al 2014).…”

“…Further research is needed to understand better how the number and size of particles produced in EC vapour compare with CC smoke. For example, Mikheev et al (2016) discovered that EC aerosol contains nanoparticles (11-25 nm in diameter) and submicron particles (96-175 nm diameter) in roughly equal concentrations, whereas Sosnowski and Kramek-Romanowska (2016) reported median diameters of 410 nm. Fuoco et al (2014) found that the amount of particulate matter in EC vapour equaled or exceeded the amount in CC smoke (average of 4.39 ± 0.42E9 particles/cm 3 for EC and 3.14 ± 0.61E9 particles/cm 3 for cigarettes), whereas Pellegrino et al (2012) found that the amount of particulate matter in CCs exceeded that of ECs by 15 times.…”