Liqiao Li

Bio: Liqiao Li is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Medicine & Aerosol. The author has an hindex of 5, co-authored 8 publications receiving 83 citations.

Effects of Electronic Cigarettes on Indoor Air Quality and Health.

Abstract: 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.

Assessing the effectiveness of using various face coverings to mitigate the transport of airborne particles produced by coughing indoors

Abstract: Exposure to respiratory droplets contributes greatly to the spread of SARS-CoV-2 virus during the COVID-19 pandemic. This study investigates the effectiveness of various face coverings to reduce co...

Effects of propylene glycol, vegetable glycerin, and nicotine on emissions and dynamics of electronic cigarette aerosols

Abstract: 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.

Electronic cigarette aerosols induce oxidative stress-dependent cell death and NF-κB mediated acute lung inflammation in mice

Abstract: 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.

Ultrafine particles: unique physicochemical properties relevant to health and disease

Abstract: Ultrafine particles (UFPs) are aerosols with an aerodynamic diameter of 0.1 µm (100 nm) or less. There is a growing concern in the public health community about the contribution of UFPs to human health. Despite their modest mass and size, they dominate in terms of the number of particles in the ambient air. A particular concern about UFPs is their ability to reach the most distal lung regions (alveoli) and circumvent primary airway defenses. Moreover, UFPs have a high surface area and a capacity to adsorb a substantial amount of toxic organic compounds. Harmful systemic health effects of PM10 or PM2.5 are often attributable to the UFP fraction. In this review, we examine the physicochemical characteristics of UFPs to enable a better understanding of the effects of these particles on human health. The characteristics of UFPs from diesel combustion will be discussed in the greatest detail because road vehicles are the primary source of UFP emissions in urban pollution hotspots. Finally, we will elaborate on the role of UFPs on global climate change, since the adverse effects of UFPs on meteorological processes and the hydrological cycle may even be more harmful to human health than their direct toxic effects. Ultrafine particles (UFPs) from auto exhaust, factory emissions, and woodburning negatively affect human health and can alter weather patterns. UFPs, particles less than 100 nanometers, smaller than the smallest bacterium, are the most common airborne particles. Their size allows them to penetrate the deepest lung passageways, sometimes carrying toxic metals or organic compounds that trigger inflammation and disease. Hyouk-Soo Kwon at the University of Ulsan, Seoul, South Korea, and coworkers have reviewed the sources and effects of UFPs. Auto engines are a primary source; recent improvements in combustion technology have resulted in production of smaller particles, with worse effects on health. UFPs have also been found to affect cloud formation and behavior, altering rainfall patterns and potentially causing flooding or drought. Understanding the properties of UFPs will help find ways to mitigate their effects.

Flow Physics of COVID-19

Abstract: Flow physics plays a key role in nearly every facet of the COVID-19 pandemic. This includes the generation and aerosolization of virus-laden respiratory droplets from a host, its airborne dispersion and deposition on surfaces, as well as the subsequent inhalation of these bioaerosols by unsuspecting recipients. Fluid dynamics is also key to preventative measures such as the use of face masks, hand-washing, ventilation of indoor environments, and even social distancing. This article summarizes what we know, and more importantly, what we need to learn about the science underlying these issues so that we are better prepared to tackle the next outbreak of COVID-19 or a similar disease.

Mining data on usage of electronic nicotine delivery systems (ENDS) from YouTube videos - eScholarship

Abstract: Objective The objective was to analyse and compare puff and exhalation duration for individuals using electronic nicotine delivery systems (ENDS) and conventional cigarettes in YouTube videos. Methods Video data from YouTube videos were analysed to quantify puff duration and exhalation duration during use of conventional tobacco-containing cigarettes and ENDS. For ENDS, comparisons were also made between ‘advertisers’ and ‘non-advertisers’, genders, brands of ENDS, and models of ENDS within one brand. Results Puff duration (mean =2.4 s) for conventional smokers in YouTube videos (N=9) agreed well with prior publications. Puff duration was significantly longer for ENDS users (mean =4.3 s) (N = 64) than for conventional cigarette users, and puff duration varied significantly among ENDS brands. For ENDS users, puff duration and exhalation duration were not significantly affected by ‘advertiser’ status, gender or variation in models within a brand. Men outnumbered women by about 5:1, and most users were between 19 and 35 years of age. Conclusions YouTube videos provide a valuable resource for studying ENDS usage. Longer puff duration may help ENDS users compensate for the apparently poor delivery of nicotine from ENDS. As with conventional cigarette smoking, ENDS users showed a large variation in puff duration (range =1.9–8.3 s). ENDS puff duration should be considered when designing laboratory and clinical trials and in developing a standard protocol for evaluating ENDS performance.

Inward and outward effectiveness of cloth masks, a surgical mask, and a face shield

Abstract: We evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin. At the most penetr...