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The rapid proliferation of electronic cigarettes (ECs) has raised significant concerns about their potential health effects on both users and bystanders. This study systematically investigates the impact of EC aerosol exposure on human alveolar epithelial cells (A549), considering variations in device parameters, nicotine concentration, and exposure type. Using a gravity-based air–liquid interface exposure system, we assessed cytotoxicity and epithelial barrier integrity by measuring cell viability and transepithelial electrical resistance (TEER). Our results indicate that EC aerosol exposure significantly reduces cell viability and disrupts monolayer integrity in a dose- and device-dependent manner. Notably, VUSE (pod-type) exposure led to a 16% decrease in viability and a 41% reduction in TEER, while VOOPOO (mod-type) exposure caused a 25% viability loss and a 61% reduction in TEER. Power settings played a critical role: at 60 W, cell viability dropped by 48% at 12 mg/mL nicotine concentration compared to 29% at 0 mg/mL. Moreover, under the same number of puffs (30 puffs), firsthand exposure resulted in a 73% viability decrease, whereas secondhand exposure showed a 47% reduction, indicating substantial bystander risks associated with EC usage. These findings underscore the importance of device specifications and exposure conditions in determining EC aerosol toxicity. The observed epithelial barrier disruption suggests increased vulnerability to respiratory diseases. Given the comparable toxicity of firsthand and secondhand aerosols, regulatory measures should extend beyond direct users to include bystander protection. This study highlights the urgent need for comprehensive toxicity assessments to inform public health policies on EC use. 

Abstract Ultraviolet germicidal irradiation (UVGI) and ozone disinfection are crucial methods for mitigating the airborne transmission of pathogenic microorganisms in high-risk settings, particularly with the emergence of respiratory viral pathogens such as SARS-CoV-2 and avian influenza viruses. This study quantitatively investigates the influence of UVGI and ozone on the viability ofE. coliin bioaerosols, with a particular focus on howE. coliviability depends on the size of the bioaerosols, a critical factor that determines deposition patterns within the human respiratory system and the evolution of bioaerosols in indoor environments. This study used a controlled small-scale laboratory chamber whereE. colisuspensions were aerosolized and subjected to varying levels of UVGI and ozone levels throughout the exposure time (2–6 s). The normalized viability ofE. coliwas found to be significantly reduced by UVGI (60–240μW s cm⁻²) as the exposure time increased from 2 to 6 s, and the most substantial reduction ofE. colinormalized viability was observed when UVGI and ozone (65–131 ppb) were used in combination. We also found that UVGI reduced the normalized viability ofE. coliin bioaerosols more significantly with smaller sizes (0.25–0.5μm) than with larger sizes (0.5–2.5μm). However, when combining UVGI and ozone, the normalized viability was higher for smaller particle sizes than for the larger ones. The findings provide insights into the development of effective UVGI disinfection engineering methods to control the spread of pathogenic microorganisms in high-risk environments. By understanding the influence of the viability of microorganisms in various bioaerosol sizes, we can optimize UVGI and ozone techniques to reduce the potential risk of airborne transmission of pathogens. 

Abstract. Accurate airborne aerosol instrumentation is required to determine thespatial distribution of ambient aerosol particles, particularly when dealingwith the complex vertical profiles and horizontal variations of atmosphericaerosols. A versatile water-based condensation particle counter (vWCPC) hasbeen developed to provide aerosol concentration measurements under variousenvironments with the advantage of reducing the health and safety concernsassociated with using butanol or other chemicals as the working fluid.However, the airborne deployment of vWCPCs is relatively limited due to thelack of characterization of vWCPC performance at reduced pressures. Giventhe complex combinations of operating parameters in vWCPCs, modeling studieshave advantages in mapping vWCPC performance. In this work, we thoroughly investigated the performance of a laminar-flowvWCPC using COMSOL Multiphysics® simulation coupled withMATLAB™. We compared it against a modified vWCPC (vWCPC model 3789, TSI,Shoreview, MN, USA). Our simulation determined the performance of particleactivation and droplet growth in the vWCPC growth tube, including thesupersaturation, Dp,kel,0 (smallest size of particle that canbe activated), Dp,kel,50 (particle size activated with 50 %efficiency) profile, and final growth particle size Dd underwide operating temperatures, inlet pressures P (30–101 kPa), and growthtube geometry (diameter D and initiator length Lini). Theeffect of inlet pressure and conditioner temperature on vWCPC 3789performance was also examined and compared with laboratory experiments. TheCOMSOL simulation result showed that increasing the temperature difference(ΔT) between conditioner temperature Tcon andinitiator Tini will reduce Dp,kel,0 and thecut-off size Dp,kel,50 of the vWCPC. In addition, loweringthe temperature midpoint(Tmid=Tcon+Tini2) increasesthe supersaturation and slightly decreases the Dp,kel. Thedroplet size at the end of the growth tube is not significantly dependent onraising or lowering the temperature midpoint but significantly decreases atreduced inlet pressure, which indirectly alters the vWCPC empirical cut-offsize. Our study shows that the current simulated growth tube geometry (D=6.3 mm and Lini=30 mm) is an optimized choice forcurrent vWCPC flow and temperature settings. The current simulation can morerealistically represent the Dp,kel for 7 nm vWCPC and alsoachieved good agreement with the 2 nm setting. Using the new simulationapproach, we provide an optimized operation setting for the 7 nm setting.This study will guide further vWCPC performance optimization forapplications requiring precise particle detection and atmospheric aerosolmonitoring. 

The usage of electronic cigarettes (ECs) has surged since their invention two decades ago. However, to date, the health effects of EC aerosol exposure are still not well understood because of insufficient data on the chemical composition of EC aerosols and the corresponding evidence of health risks upon exposure. Herein, we quantified the metals in primary and secondhand aerosols generated by three brands of ECs. By combining aerosol filter sampling and inductively coupled plasma mass spectrometry (ICP-MS), we assessed the mass of metals as a function of EC flavoring, nicotine concentration, device power, puff duration, and aging of the devices. The masses of Cr, Cu, Mn, Ni, Cu, and Zn were consistently high across all brands in the primary and secondhand aerosols, some of which were above the regulated maximum daily intake amount, especially for Cr and Ni with mass (nanograms per 10 puffs) emitted at 117 ± 54 and 50 ± 24 (JUUL), 125 ± 77 and 219 ± 203 (VOOPOO), and 33 ± 10 and 27 ± 2 (Vapor4Life). Our analysis indicates that the metals are predominantly released from the EC liquid, potentially through mechanisms such as bubble bursting or the vaporization of metal–organic compounds. High metal contents were also observed in simulated secondhand aerosols, generally 80–90% of those in primary aerosols. Our findings provide a more detailed understanding of the metal emission characteristics of EC for assessing its health effects and policymaking.