Numerical study of transient indoor airflow and virus-laden droplet dispersion: Impact of interactive human movement

Bioaerosol risk assessment of air curtain ventilation in isolation wards based on static and dynamic scenarios

Due to high concentrations of virus-carrying bioaerosols, the healthcare worker (HCW) faces a high risk of infection in isolation wards. Air curtain ventilation (ACV) has the potential to reduce the infection risk in healthy people. This work studied the effect of ACV on the diffusion of bioaerosols released when the patient was speaking. Combined with the improved Lagrangian-based Wells-Riley model and numerical simulation, the infection risk of HCWs was quantitatively predicted. The results show that the ACV mode performed better in bioaerosol removal and HCW protection than the original downward ventilation mode. Under the same ventilation conditions, both the suspended bioaerosol concentration and HCW infection risk were higher for the sitting case than for the lying case. For the same ventilation rate, increasing the supply velocity was more effective in reducing risk than increasing the air curtain width. The HCW infection risk decreased to 2.34 × 10-7, when the velocity and width were 1.34 m/s and 0.1 m, respectively. The ACV with a larger length-to-width ratio improved bioaerosol removal and infection risk reduction. Bioaerosol concentrations and infection risk were slightly higher in the dynamic scenario than in the static scenario, but no significant difference was observed. This work can provide a reference for the design and application of ACV in isolation wards.

Perspectives on aerosol inhalability: concepts and applications

The original motivation for the aerosol inhalability convention was to account for the fact that the inhalation efficiency of particles can cause the composition of the particle-containing air that is inhaled into the mouth and nose to differ significantly from the composition of the ambient air. Therefore, without appropriate adjustments for the inhalation efficiency of particles, air samples could over- or underestimate the actual exposures of inhaled materials, possibly compromising some workplace air standards. Subsequently, the concepts and applications of inhalability and inhalability sampling have been expanded to inhalation exposures outside of the workplace, including general human populations, medical patients, cell cultures, and animal research subjects. As described in this commentary, some of these applications have occurred in ways that could misrepresent actual exposures. Scientific advances in the understanding and applications of inhalability-related concepts are needed. Such advances will best be achieved through multidisciplinary collaborations involving modeling, wind tunnel mannequin and human subject studies, and health effects studies involving input from aerosol scientists, engineers, physiologists, anatomists, physicians, veterinarians, mathematical modelers, and regulators.

Evaluating infection risks in buses based on passengers' dynamic temporal and typical spatial scenarios: A case study of COVID-19

Conventional buses, as an indispensable part of the urban public transport system, impose cross-infection risks on passengers. To assess differential risks due to dynamic staying durations and locations, this study considered four spatial distributions (i = 1-4) and six temporal scenarios (j = 1-6) of buses. Based on field measurements and a risk assessment approach combining both short-range and room-scale effects, risks are evaluated properly. The results showed that temporal asynchrony between infected and susceptible individuals significantly affects disease transmission rates. The Control Case assumes that infected and susceptible individuals enter and leave synchronously. However, ignoring temporal asynchrony scenarios, i.e., the Control Case, resulted in overestimation (+30.7 % to +99.6 %) or underestimation (-15.2 % to -69.9 %) of the actual risk. Moreover, the relative difference ratios of room-scale risks between the Control Case and five temporal scenarios are impacted by ventilation. Short-range risk exists only if infected and susceptible individuals have temporal overlap on the bus. Considering temporal and spatial asynchrony, a more realistic total reproduction number (R) can be obtained. Subsequently, the total R was assessed under five temporal scenarios. On average, for the Control Case, the total R was estimated to be +27.3 % higher than j = 1, -9.3 % lower than j = 2, +12.8 % higher than j = 3, +33.0 % lower than j = 4, and + 77.6 % higher than j = 5. This implies the need for a combination of active prevention and real-time risk monitoring to enable rigid travel demand and control the spread of the epidemic.

Perspectives on human movement considerations in indoor airflow assessment: a comprehensive data-driven systematic review

Understanding particle dispersion characteristics in indoor environments is crucial for revising infection prevention guidelines through optimized engineering control. The secondary wake flow induced by human movements can disrupt the local airflow field, which enhances particle dispersion within indoor spaces. Over the years, researchers have explored the impact of human movement on indoor air quality (IAQ) and identified noteworthy findings. However, there is a lack of a comprehensive review that systematically synthesizes and summarizes the research in this field. This paper aims to fill that gap by providing an overview of the topic and shedding light on emerging areas. Through a systematic review of relevant articles from the Web of Science database, the study findings reveal an emerging trend and current research gaps on the topic titled Impact of Human Movement in Indoor Airflow (HMIA). As an overview, this paper explores the effect of human movement on human microenvironments and particle resuspension in indoor environments. It delves into the currently available methods for assessing the HMIA and proposes the integration of IoT sensors for potential indoor airflow monitoring. The present study also emphasizes incorporating human movement into ventilation studies to achieve more realistic predictions and yield more practical measures. This review advances knowledge and holds significant implications for scientific and public communities. It identifies future research directions and facilitates the development of effective ventilation strategies to enhance indoor environments and safeguard public health.