In Vivo Study of Aerosol, Droplets and Splatter Reduction in Dentistry

Oral health care workers (OHCW) are exposed to pathogenic microorganisms during dental aerosol-generating procedures. Technologies aimed at the reduction of aerosol, droplets and splatter are essential. This in vivo study assessed aerosol, droplet and splatter contamination in a simulated clinical scenario. The coolant of the high-speed air turbine was colored with red concentrate. The red aerosol, droplets and splatter contamination on the wrists of the OHCW and chests of the OHCW/volunteer protective gowns, were assessed and quantified in cm2. The efficacy of various evacuation strategies was assessed: low-volume saliva ejector (LV) alone, high-volume evacuator (HV) plus LV and an extra-oral dental aerosol suction device (DASD) plus LV. The Kruskal–Wallis rank-sum test for multiple independent samples with a post-hoc test was used. No significant difference between the LV alone compared to the HV plus LV was demonstrated (p = 0.372059). The DASD combined with LV resulted in a 62% reduction of contamination of the OHCW. The HV plus LV reduced contamination by 53% compared to LV alone (p = 0.019945). The DASD demonstrated a 50% reduction in the contamination of the OHCWs wrists and a 30% reduction in chest contamination compared to HV plus LV. The DASD in conjunction with LV was more effective in reducing aerosol, droplets and splatter than HV plus LV.

The Post-COVID-19 Era: Interdisciplinary Demands of Contagion Surveillance Mass Spectrometry for Future Pandemics

Mass spectrometry (MS) can become a potentially useful instrument type for aerosol, droplet and fomite (ADF) contagion surveillance in pandemic outbreaks, such as the ongoing SARS-CoV-2 pandemic. However, this will require development of detection protocols and purposing of instrumentation for in situ environmental contagion surveillance. These approaches include: (1) enhancing biomarker detection by pattern recognition and machine learning; (2) the need for investigating viral degradation induced by environmental factors; (3) representing viral molecular data with multidimensional data transforms, such as van Krevelen diagrams, that can be repurposed to detect viable viruses in environmental samples; and (4) absorbing engineering attributes for developing contagion surveillance MS from those used for astrobiology and chemical, biological, radiological, nuclear (CBRN) monitoring applications. Widespread deployment of such an MS-based contagion surveillance could help identify hot zones, create containment perimeters around them and assist in preventing the endemic-to-pandemic progression of contagious diseases.

Droplet and Aerosol Suspension Times in Ambient Air in Confined Spaces and Transmission of COVID-19: Influence of Environmental Factors

The COVID‑19 pandemic, alternatively known as the coronavirus pandemic, is an unfolding pandemic of coronavirus disease 2019 (COVID‑19) across the entire globe in an unprecedented proportion. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2. The mode of transmission of COVID-19 is a subject of intense research. The airborne transmission is one prime possibility. Breathing and talking are natural processes which generate exhaled particles. The exhaled air is an aerosol/droplet composed of naturally produced particulates of varying size. The duration over which the aerosols/droplets are suspended in the air is an important factor. Long suspended aerosols/droplets are potential source of transmission, particularly in confined spaces. We have calculated times of suspension by considering various environmental factors, namely, the ambient temperature and relative humidity in a confined space, in this work. Both temperature and relative humidity affect the suspension time of the exhaled aerosols/droplets with varying degree. The effects of environmental factors are significant for aerosols, particularly for those with small radii. We have discussed the possible implications of our findings in this paper.

Individual Aerosol Droplet pH Measurement via a Ratio-metric Raman Method Using Aerosol Optical Tweezers: Evaluation of Thermodynamic and Activity Models

<p>Measuring pH in individual aerosol droplet is essential for understanding and estimating physicochemical processes within aerosol microenvironments. Recently, aerosol optical tweezers coupling with Raman spectroscopy have been applied to measure the pH of single trapped microdroplets by utilizing conjugate acid-base equilibrium to infer pH shifts. However, such measurements are easily affected by many factors such as variations in detecting volumes and laser intensities, making it hard to directly determine these acid and base concentrations through their respective peak areas. To overcome these problems and accurately measure the concentrations of SO<sub>4</sub><sup>2-</sup> and HSO<sub>4</sub><sup>−</sup> within individual NaHSO<sub>4</sub> microdroplets, in this study a ratio-metric spectroscopic method is developed based on the peak area ratio of ν(SO<sub>4</sub><sup>2−</sup>)/ν(OH) and ν(HSO<sub>4</sub><sup>−</sup>)/ν(OH). Combined with the ion balance and ion activity coefficients, droplet pH is determined unambiguously. These experiment results were further used to evaluate the performance of activity models and thermodynamic models associated with aerosol pH, ion concentration and activity coefficient predictions. Pitzer, Simonson, and Clegg (PSC) model provides the best predictions of ion activity coefficients Extended Aerosol Inorganics Model vision IV (E-AIM IV) works well over a wide NaHSO<sub>4</sub> concentration range (0.4-8.8 mol/kg), while ACCENT Pitzer model predictions have extremely good agreement with the experiment results in low NaHSO<sub>4</sub> concentration condition (≤2.0 mol/kg). By contrast, ISORROPIA II shows relatively poor performance as compared with E-AIM IV.</p>

Comprehensive characterization of protective face coverings made from household fabrics

Background Face coverings constitute an important strategy for containing pandemics, such as COVID-19. Infection from airborne respiratory viruses including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) can occur in at least three modes; tiny and/or dried aerosols (typically < 1.0 μm) generated through multiple mechanisms including talking, breathing, singing, large droplets (> 0.5 μm) generated during coughing and sneezing, and macro drops transmitted via fomites. While there is a growing number of studies looking at the performance of household materials against some of these situations, to date, there has not been any systematic characterization of household materials against all three modes. Methods A three-step methodology was developed and used to characterize the performance of 21 different household materials with various material compositions (e.g. cotton, polyester, polypropylene, cellulose and blends) using submicron sodium chloride aerosols, water droplets, and mucous mimicking macro droplets over an aerosol-droplet size range of ~ 20 nm to 0.6 cm. Results Except for one thousand-thread-count cotton, most single-layered materials had filtration efficiencies < 20% for sub-micron solid aerosols. However, several of these materials stopped > 80% of larger droplets, even at sneeze-velocities of up to 1700 cm/s. Three or four layers of the same material, or combination materials, would be required to stop macro droplets from permeating out or into the face covering. Such materials can also be boiled for reuse. Conclusion Four layers of loosely knit or woven fabrics independent of the composition (e.g. cotton, polyester, nylon or blends) are likely to be effective source controls. One layer of tightly woven fabrics combined with multiple layers of loosely knit or woven fabrics in addition to being source controls can have sub-micron filtration efficiencies > 40% and may offer some protection to the wearer. However, the pressure drop across such fabrics can be high (> 100 Pa).

Aerosol droplet-size distribution and airborne nicotine portioning in particle and gas phases emitted by electronic cigarettes

The reliable characterization of particle size distribution and nicotine delivery emitted by electronic cigarettes (ECs) is a critical issue in their design. Indeed, a better understanding of how nicotine is delivered as an aerosol with an appropriate aerodynamic size is a necessary step toward obtaining a well-designed nicotine transfer from the respiratory tract to the bloodstream to better satisfy craving and improve smoking cessation rates. To study these two factors, recent models of EC devices and a dedicated vaping machine were used to generate aerosols under various experimental conditions, including varying the EC power level using two different types of atomizers. The aerodynamic particle sizing of the resulting aerosol was performed using a cascade impactor. The nicotine concentration in the refill liquid and the aerosol droplet was quantified by liquid chromatography coupled with a photodiode array. The vaporization process and the physical and chemical properties of the EC aerosol were very similar at 15 watts (W) and 25 W using the low-power atomizer but quite distinct at 50 W using the high-power atomizer, as follows: (1) the mass median aerodynamic diameters ranged from 1.06 to 1.19 µm (µm) for low power and from 2.33 to 2.46 µm for high power; (2) the nicotine concentrations of aerosol droplets were approximately 11 mg per milliliter (mg/mL) for low power and 17 mg/mL for high power; and (3) the aerosol droplet particle phase of the total nicotine mass emitted by EC was 60% for low power and 95% for high power. The results indicate that varying the correlated factors (1) the power level and (2) the design of atomizer (including the type of coil and the value of resistance used) affects the particle-size distribution and the airborne nicotine portioning between the particle phase and the gas phase in equilibrium with the airborne droplets.