Study on droplet dispersion influenced by ventilation and source configuration in classroom settings using low‐cost sensor network

The COVID‐19 virus can transmit through airborne expiratory droplets and thus, the viral transmission can take place between the occupants in the isolated room. With the school re-opening under the current COVID‐19 pandemic, it is urgent to improve the classroom ventilation system to mitigate the risk of virus transmission. The present study developed a particle concentration monitoring network (PCMN) using low‐cost sensors and deployed it to explore the dispersion of the droplet particles under different ventilation settings and aerosol configurations. Our experiment shows the advance of using a low‐cost sensor network on spatiotemporal air monitoring and demonstrates indoor particle concentration level and distribution are strongly impacted by the ventilation setting and source location. Two recommendations on reducing the viral risk in the classroom were derived from the study. The first is the respiratory droplet source, e.g., the instructor, should be in the location such that the particle dispersion opposes the ventilation flow. The second is the air handling unit (AHU) and fan coil unit (FCU) should be both turned on during class hours despite whether there is a need for thermal comfort, as it allows higher and more uniform ventilation flow to resolve the issue of the dead air zone. © The Author(s).

An experimentally validated analytical model for aerosol number concentration reduction in classrooms

To predict the aerosol number concentration decay in modern classrooms, this study derived an analytical model that addresses various indoor factors, viz., the filtration efficiency of air ventilation systems, effects of indoor air cleaners, particle deposition on walls, and particle emission from occupants. We also conducted experimental measurements to determine the wall-loss coefficient and the occupants’ particle generation rate, and the modeling results agreed with the experimental data reasonably well. Additionally, we investigated the behavior of the particle concentration decay in different ventilation scenarios. The model has been incorporated into web-based software that is freely available to the public. © The Author(s).

Expression of SARS-CoV-2 entry genes ACE2 and TMPRSS2 at single cell resolution in the peripartum decidua

Angiotensin-converting enzyme 2 (ACE2) is the key receptor for severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). However, the susceptibility of the decidua to infection during the peripartum period has not been explored, even though this may affect vertical transmission. The objective of this study was to investigate the expression of ACE2 and related genes in the decidua during delivery. Here, single-cell RNA sequencing was used to characterize the transcriptomes of decidual cells before and after the onset of labor. During the peripartum period, ACE2 expression was highly heterogeneous. ACE2 was expressed principally in decidual stromal cells, uterine smooth muscle cells, and extravillous trophoblasts. Comparison of the transcriptomes of ACE2-positive and ACE2-negative cells indicated that ACE2-positive cells exhibited integrin clusters on the cell surface interactions. ACE2-positive cells were compared before and after labor onset. After delivery, the number of ACE2-positive cells was slightly higher than before delivery. Before labor onset, ACE2-positive decidual stromal cells were in the regulation of membrane protein ectodomain proteolysis cluster. After labor onset, the upregulated genes changed to include cell junction assembly genes. The susceptibility of decidual cells to SARS-CoV-2 infection is thus heterogeneous during the peripartum period. © 2021 E-Century Publishing Corporation. All rights reserved.

Alternative face masks made of common materials for general public: Fractional filtration efficiency and breathability perspective

As COVID-19 pandemic has caused more than 24 million confirmed cases globally (as of August 28th, 2020), it is critical to slow down the spreading of SARS-CoV-2 to protect the healthcare system from overload. Wearing a respirator or a mask has been proven as an effective method to protect both the wearer and others, but commercially available respirators and masks should be reserved for healthcare workers under a currently desperate shortage. The use of alternative materials becomes an option for the general public to make the do-it-yourself (DIY) masks, with their efficacy seldom reported. In this study, we tested commercial respirators and masks, furnace filters, vacuum cleaner filters, and common household materials. We evaluated the materials’ fractional filtration efficiency and breathing resistance, which are primary factors affecting respiratory protection. To compare the efficiency-resistance tradeoff, the figure of merit of each tested common material was also calculated. Filter media with electrostatic charges (electret) is recommended due to its high efficiency with low flow resistance;multiple-layer household fabrics and sterilization wraps are acceptable materials;a coffee filter is inadvisable due to its low efficiency. The outcome of this study can not only offer guidance for the general public under the current pandemic but also suggest the appropriate alternative respiratory protection materials under heavy air pollution episodes. © The Author(s).