The airborne transmission of infection between flats in high-rise residential buildings: Tracer gas simulation

The Wells-Riley model revisited: Randomness, heterogeneity, and transient behaviours

The Wells-Riley model has been widely used to estimate airborne infection risk, typically from a deterministic point of view (i.e., focusing on the average number of infections) or in terms of a per capita probability of infection. Some of its main limitations relate to considering well-mixed air, steady-state concentration of pathogen in the air, a particular amount of time for the indoor interaction, and that all individuals are homogeneous and behave equally. Here, we revisit the Wells-Riley model, providing a mathematical formalism for its stochastic version, where the number of infected individuals follows a Binomial distribution. Then, we extend the Wells-Riley methodology to consider transient behaviours, randomness, and population heterogeneity. In particular, we provide analytical solutions for the number of infections and the per capita probability of infection when: (i) susceptible individuals remain in the room after the infector leaves, (ii) the duration of the indoor interaction is random/unknown, and (iii) infectors have heterogeneous quanta production rates (or the quanta production rate of the infector is random/unknown). We illustrate the applicability of our new formulations through two case studies: infection risk due to an infectious healthcare worker (HCW) visiting a patient, and exposure during lunch for uncertain meal times in different dining settings. Our results highlight that infection risk to a susceptible who remains in the space after the infector leaves can be nonnegligible, and highlight the importance of incorporating uncertainty in the duration of the indoor interaction and the infectivity of the infector when estimating risk.

A CFD-based framework to assess airborne infection risk in buildings

The COVID-19 pandemic has prompted huge efforts to further the scientific knowledge of indoor ventilation and its relationship to airborne infection risk. Exhaled infectious aerosols are spread and inhaled as a result of room airflow characteristics. Many calculation methods and assertions on risk assume 'well-mixed' flow conditions. However, ventilation in buildings is complex and often not showing well-mixed conditions. Ventilation guidance is typically based on the provision of generic minimum ventilation flow rates for a given space, irrespective of the effectiveness in the delivery of the supply air. Furthermore, the airflow might be heavily affected by the season, the HVAC ventilation, or the opening of windows, which would potentially generate draughts and non-uniform conditions. As a result, fresh air concentration would be variable depending upon a susceptible receptor's position in a room and, therefore, associated airborne infection risk. A computational fluid dynamics (CFD) and dynamic thermal modelling (DTM) framework is proposed to assess the influence of internal airflow characteristics on airborne infection risk. A simple metric is proposed, the hourly airborne infection rate (HAI) which can easily help designers to stress-test the ventilation within a building under several conditions. A case study is presented, and the results clearly demonstrate the importance of understanding detailed indoor airflow characteristics and associated concentration patterns in order to provide detailed design guidance, e.g. occupancy, supply air diffusers and furniture layouts, to reduce airborne infection risk.

CFD Simulations of Ventilation and Interunit Dispersion in Dormitory Complex: A Case Study of Epidemic Outbreak in Shanghai

Since the beginning of March 2022, a new round of COVID-19 outbreaks in Shanghai has led to a sharp increase in the number of infected people. It is important to identify possible pollutant transmission routes and predict potential infection risks for infectious diseases. Therefore, this study investigated the cross-diffusion of pollutants caused by natural ventilation, including external windows and indoor ventilation windows, under three wind directions in a densely populated building environment with the CFD method. In this study, CFD building models were developed based on an actual dormitory complex and surrounding buildings under realistic wind conditions to reproduce the airflow fields and transmission paths of pollutants. This paper adopted the Wells-Riley model to assess the risk of cross-infection. The biggest risk of infection was when a source room was located on the windward side, and the risk of infection in other rooms on the same side as the source room was large in the windward direction. When pollutants were released from room 8, north wind resulted in the highest concentration of pollutants in room 28, reaching 37.8%. This paper summarizes the transmission risks related to the indoor and outdoor environments of compact buildings.

Computational decision-support tools for urban design to improve resilience against COVID-19 and other infectious diseases: A systematic review

The COVID-19 pandemic highlighted the need for decision-support tools to help cities become more resilient to infectious diseases. Through urban design and planning, non-pharmaceutical interventions can be enabled, impelling behaviour change and facilitating the construction of lower risk buildings and public spaces. Computational tools, including computer simulation, statistical models, and artificial intelligence, have been used to support responses to the current pandemic as well as to the spread of previous infectious diseases. Our multidisciplinary research group systematically reviewed state-of-the-art literature to propose a toolkit that employs computational modelling for various interventions and urban design processes. We selected 109 out of 8,737 studies retrieved from databases and analysed them based on the pathogen type, transmission mode and phase, design intervention and process, as well as modelling methodology (method, goal, motivation, focus, and indication to urban design). We also explored the relationship between infectious disease and urban design, as well as computational modelling support, including specific models and parameters. The proposed toolkit will help designers, planners, and computer modellers to select relevant approaches for evaluating design decisions depending on the target disease, geographic context, design stages, and spatial and temporal scales. The findings herein can be regarded as stand-alone tools, particularly for fighting against COVID-19, or be incorporated into broader frameworks to help cities become more resilient to future disasters.

Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

Relationships between building attributes and COVID-19 infection in London

In the UK, all domestic COVID-19 restrictions have been removed since they were introduced in March 2020. After illustrating the spatial-temporal variations in COVID-19 infection rates across London, this study then particularly aimed to examine the relationships of COVID-19 infection rates with building attributes, including building density, type, age, and use, since previous studies have shown that the built environment plays an important role in public health. Multisource data from national health services and the London Geomni map were processed with GIS techniques and statistically analysed. From March 2020 to April 2022, the infection rate of COVID-19 in London was 3,159.28 cases per 10,000 people. The spatial distribution across London was uneven, with a range from 1,837.88 to 4,391.79 per 10,000 people. During this period, it was revealed that building attributes played a significant role in COVID-19 infection. It was noted that higher building density areas had lower COVID-19 infection rates in London. Moreover, a higher percentage of historic or flat buildings tended to lead to a decrease in infection rates. In terms of building use, the rate of COVID-19 infection tended to be lower in public buildings and higher in residential buildings. Variations in the infection rate were more sensitive to building type; in particular, the percentage of residents living in flats contributed the most to variations in COVID-19 infection rates, with a value of 2.3%. This study is expected to provide support for policy and practice towards pandemic-resilient architectural design.

Influencing Factors on Airflow and Pollutant Dispersion around Buildings under the Combined Effect of Wind and Buoyancy-A Review

With the rapid growth of populations worldwide, air quality has become an increasingly important issue related to the health and safety of city inhabitants. There are quite a few factors that contribute to urban air pollution; the majority of studies examining the issue are concerned with environmental conditions, building geometries, source characteristics and other factors and have used a variety of approaches, from theoretical modelling to experimental measurements and numerical simulations. Among the environmental conditions, solar-radiation-induced buoyancy plays an important role in realistic conditions. The thermal conditions of the ground and building façades directly affect the wind field and pollutant dispersion patterns in the microclimate. The coupling effect of wind and buoyancy on the urban environment are currently hot and attractive research topics. Extensive studies have been devoted to this field, some focused on the street canyon scale, and have found that thermal effects do not significantly affect the main airflow structure in the interior of the street canyon but strongly affect the wind velocity and pollutant concentration at the pedestrian level. Others revealed that the pollutant dispersion routes can be obviously different under various Richardson numbers at the scale of the isolated building. The purpose of this review is therefore to systematically articulate the approaches and research outcomes under the combined effect of wind and buoyancy from the street canyon scale to an isolated building, which should provide some insights into future modelling directions in environmental studies.

Vertical outbreak of COVID-19 in high-rise buildings: The role of sewer stacks and prevention measures

COVID-19 outbreaks in high-rise buildings suggested the transmission route of fecal-aerosol-inhalation due to the involvement of viral aerosols in sewer stacks. The vertical transmission is likely due to the failure of water traps that allow viral aerosols to spread through sewer stacks. This process can be further facilitated by the chimney effect in vent stack, extract ventilation in bathrooms, or wind-induced air pressure fluctuations. To eliminate the risk of such vertical disease spread, the installation of protective devices is highly encouraged in high-rise buildings. Although the mechanism of vertical pathogen spread through drainage pipeline has been illustrated by tracer gas or microbial experiments and numerical modeling, more research is needed to support the update of regulatory and design standards for sewerage facilities.

Airborne infection risk of inter-unit dispersion through semi-shaded openings: A case study of a multi-storey building with external louvers

Building design for natural ventilation and indoor air quality have become increasingly important during the past decades. Investigating airflow routes of airborne transmission and evaluating the potential infection risk in the multi-storey building is helpful to the reduction of airborne transmission. Therefore, this study applies computational fluid dynamics simulations to investigate the inter-unit dispersion pattern of gaseous pollutant between different units through semi-shaded openings. The airflow exchange and pollutant dispersion in a multi-storey building is driven by wind-induced natural ventilation. External shading louvers, which are widely used in building facades to reduce heat gain from solar radiation, are chosen to establish the semi-shaded environment. Experimental validation is performed to make sure the accuracy of numerical settings in airflow investigation of semi-shaded openings. The airflow characteristics around semi-shaded openings is analyzed in the numerical simulations. The re-entry ratio of tracer gas and the airborne infection risk of COVID-19 is investigated in the cases with different louvers' locations and source units. The results show that the airflow is commonly slower in the semi-shaded space between louvers and openings. But the ventilation rate is not always consistent with the airflow speed because of the diversion effect from louver slats. The inter-unit infectious risk in the worst unit rises from 7.82% to 26.17% for windward shading, while it rises from 7.89% to 22.52% for leeward shading. These results are helpful to the further understanding of inter-unit transmission of infectious respiratory aerosols through external openings with complex structures.

Airborne transmission of COVID-19 virus in enclosed spaces: An overview of research methods

Since the outbreak of COVID-19 in December 2019, the severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) has spread worldwide. This study summarized the transmission mechanisms of COVID-19 and their main influencing factors, such as airflow patterns, air temperature, relative humidity, and social distancing. The transmission characteristics in existing cases are providing more and more evidence that SARS CoV-2 can be transmitted through the air. This investigation reviewed probabilistic and deterministic research methods, such as the Wells-Riley equation, the dose-response model, the Monte-Carlo model, computational fluid dynamics (CFD) with the Eulerian method, CFD with the Lagrangian method, and the experimental approach, that have been used for studying the airborne transmission mechanism. The Wells-Riley equation and dose-response model are typically used for the assessment of the average infection risk. Only in combination with the Eulerian method or the Lagrangian method can these two methods obtain the spatial distribution of airborne particles' concentration and infection risk. In contrast with the Eulerian and Lagrangian methods, the Monte-Carlo model is suitable for studying the infection risk when the behavior of individuals is highly random. Although researchers tend to use numerical methods to study the airborne transmission mechanism of COVID-19, an experimental approach could often provide stronger evidence to prove the possibility of airborne transmission than a simple numerical model. All in all, the reviewed methods are helpful in the study of the airborne transmission mechanism of COVID-19 and epidemic prevention and control.

Infection risk of SARS-CoV-2 in a dining setting: Deposited droplets and aerosols

Considering that safe-distancing and mask-wearing measures are not strictly enforced in dining settings in the context of SARS-CoV-2, the infection risks of patrons in a dining outlet (e.g., a cafe) is assessed in this study. The size-resolved aerosol emission rate (AER) and droplets deposition rate (DDR) on dining plates from speaking were obtained through chamber measurements and droplet deposition visualization via fluorescent imaging technique (FIT), respectively. The AER from speaking was 24698 #/min in the size range of 0.3-5.5 μm, while the DDR was 365 #/min in the size range of 43-2847 μm. Furthermore, an infection risk model was adopted and revised to evaluate the infection risk of 120 diners for a "3-h event" in the cafe. In a four-person dining setting around a rectangular table, a diner seated diagonally across an infected person posed the least infection risk due to the deposited droplets on dining plates. The deposited droplets on a dining plate were dominant in possible viral transmission as compared to the long-range airborne route when a diner shared a table with the infected person. Yet, long-range airborne transmission had the potential to infect other diners in the cafe, even resulting in super-spreading events. A fresh air supply of 12.1-17.0 L/s per person is recommended for the cafe to serve 4-20 diners concurrently to minimize infection risks due to aerosols. Current ventilation standards (e.g., 8-10 L/s per person) for a cafe are not enough to avoid the airborne transmission of SARS-CoV-2.

Airborne and aerosol pathogen transmission modeling of respiratory events in buildings: An overview of computational fluid dynamics

Pathogen droplets released from respiratory events are the primary means of dispersion and transmission of the recent pandemic of COVID-19. Computational fluid dynamics (CFD) has been widely employed as a fast, reliable, and inexpensive technique to support decision-making and to envisage mitigatory protocols. Nonetheless, the airborne pathogen droplet CFD modeling encounters limitations due to the oversimplification of involved physics and the intensive computational demand. Moreover, uncertainties in the collected clinical data required to simulate airborne and aerosol transport such as droplets' initial velocities, tempo-spatial profiles, release angle, and size distributions are broadly reported in the literature. There is a noticeable inconsistency around these collected data amongst many reported studies. This study aims to review the capabilities and limitations associated with CFD modeling. Setting the CFD models needs experimental data of respiratory flows such as velocity, particle size, and number distribution. Therefore, this paper briefly reviews the experimental techniques used to measure the characteristics of airborne pathogen droplet transmissions together with their limitations and reported uncertainties. The relevant clinical data related to pathogen transmission needed for postprocessing of CFD data and translating them to safety measures are also reviewed. Eventually, the uncertainty and inconsistency of the existing clinical data available for airborne pathogen CFD analysis are scurtinized to pave a pathway toward future studies ensuing these identified gaps and limitations.

Beyond well-mixed: A simple probabilistic model of airborne disease transmission in indoor spaces

We develop a simple model for assessing risk of airborne disease transmission that accounts for non-uniform mixing in indoor spaces and is compatible with existing epidemiological models. A database containing 174 high-resolution simulations of airflow in classrooms, lecture halls, and buses is generated and used to quantify the spatial distribution of expiratory droplet nuclei for a wide range of ventilation rates, exposure times, and room configurations. Imperfect mixing due to obstructions, buoyancy, and turbulent dispersion results in concentration fields with significant variance. The spatial non-uniformity is found to be accurately described by a shifted lognormal distribution. A well-mixed mass balance model is used to predict the mean, and the standard deviation is parameterized based on ventilation rate and room geometry. When employed in a dose-response function risk model, infection probability can be estimated considering spatial heterogeneity that contributes to both short- and long-range transmission.

Impact of Indoor-Outdoor Temperature Difference on Building Ventilation and Pollutant Dispersion within Urban Communities

Mechanical ventilation consumes a huge amount of global energy. Natural ventilation is a crucial solution for reducing energy consumption and enhancing the capacity of atmospheric self-purification. This paper evaluates the impacts of indoor-outdoor temperature differences on building ventilation and indoor-outdoor air pollutant dispersion in urban areas. The Computational Fluid Dynamics (CFD) method is employed to simulate the flow fields in the street canyon and indoor environment. Ventilation conditions of single-side ventilation mode and cross-ventilation mode are investigated. Air change rate, normalized concentration of traffic-related air pollutant (CO), intake fraction and exposure concentration are calculated to for ventilation efficiency investigation and exposure assessment. The results show that cross ventilation increases the air change rate for residential buildings under isothermal conditions. With the indoor-outdoor temperature difference, heating could increase the air change rate of the single-side ventilation mode but restrain the capability of the cross-ventilation mode in part of the floors. Heavier polluted areas appear in the upstream areas of single-side ventilation modes, and the pollutant can diffuse to middle-upper floors in cross-ventilation modes. Cross ventilation mitigates the environmental health stress for the indoor environment when indoor-outdoor temperature difference exits and the personal intake fraction is decreased by about 66% compared to the single-side ventilation. Moreover, the existence of indoor-outdoor temperature differences can clearly decrease the risk of indoor personal exposure under both two natural ventilation modes. The study numerically investigates the building ventilation and pollutant dispersion in the urban community with natural ventilation. The method and the results are helpful references for optimizing the building ventilation plan and improving indoor air quality.

Aerosol Dynamics Model for Estimating the Risk from Short-Range Airborne Transmission and Inhalation of Expiratory Droplets of SARS-CoV-2

The highly infectious SARS-CoV-2 novel coronavirus has resulted in a global pandemic. More than a hundred million people are already impacted, with infected numbers expected to go up. Coughing, sneezing, and even talking emit respiratory droplets which can carry infectious viruses. It is important to understand how the exhaled particles move through air to an exposed person to better predict the airborne transmission impacts of SARS-CoV-2. There are many studies conducted on the airborne spread of viruses causing diseases such as SARS and measles; however, there are very limited studies that couple the transport characteristics with the aerosol dynamics of the droplets. In this study, a comprehensive model for simultaneous droplet evaporation and transport due to diffusion, convection, and gravitational settling is developed to determine the near spatial and temporal concentration of the viable virus exhaled by the infected individual. The exposure to the viable virus is estimated by calculating the respiratory deposition, and the risk of infection is determined using a dose-response model. The developed model is used to quantify the risk of short-range airborne transmission of SARS-CoV-2 from inhalation of virus-laden droplets when an infected individual is directly in front of the person exposed and the surrounding air is stagnant. The effect of different parameters, such as viral load, infectivity factor, emission sources, physical separation, exposure time, ambient air velocity, dilution, and mask usage, is determined on the risk of exposure.

Enlightenment of re-entry airflow: The path of the airflow and the airborne pollutants transmission in buildings

Viable aerosols in the airflow may increase the risk of occupants contracting diseases. Natural ventilation is common in buildings and is accompanied by re-entry airflow during the ventilation process. If the re-entry airflow contains toxic or infectious species, it may cause potential harm to residents. One of the Covid-19 outbreaks occurred in a public residential building at Luk Chuen House (LC-House) in Hong Kong. It is highly suspected that the outbreak of the disease is related to the re-entry airflow. The study attempts to explain and discuss possible causes of the outbreak. In order to understand the impact of airflow on the outbreak, a public residential building similar to LC-House was used in the study. Two measurements M - I and M - II with the same settings were conducted for a sampling unit in the corridor under low and strong wind conditions respectively. The sampling unit and the tracer gas carbon dioxide (CO₂) were used to simulate the index unit and infectious contaminated airflow respectively. The CO₂ concentrations of the unit and corridor were measured simultaneously. Two models of Traditional Single-zone model (TSZ-model) and New Dual-zone model (NDZ-model) were used in the analysis. By comparing the ACH values obtained from the two models, it is indicated that the re-entry airflow of the unit is related to the corridor wind speeds and this provides a reasonable explanation for the outbreak in LC-House, and believes that the results can help understand the recent frequent cluster outbreaks in other residential buildings.

Spatial analysis of the impact of urban geometry and socio-demographic characteristics on COVID-19, a study in Hong Kong

The World Health Organization considered the wide spread of COVID-19 over the world as a pandemic. There is still a lack of understanding of its origin, transmission, and treatment methods. Understanding the influencing factors of COVID-19 can help mitigate its spread, but little research on the spatial factors has been conducted. Therefore, this study explores the effects of urban geometry and socio-demographic factors on the COVID-19 cases in Hong Kong. For each patient, the places they visited during the incubation period before going to hospital were identified, and matched with corresponding attributes of urban geometry (i.e., building geometry, road network and greenspace) and socio-demographic factors (i.e., demographic, educational, economic, household and housing characteristics) based on the coordinates. The local cases were then compared with the imported cases using stepwise logistic regression, logistic regression with case-control of time, and least absolute shrinkage and selection operator regression to identify factors influencing local disease transmission. Results show that the building geometry, road network and certain socio-economic characteristics are significantly associated with COVID-19 cases. In addition, the results indicate that urban geometry is playing a more important role than socio-demographic characteristics in affecting COVID-19 incidence. These findings provide a useful reference to the government and the general public as to the spatial vulnerability of COVID-19 transmission and to take appropriate preventive measures in high-risk areas.

The role of computational fluid dynamics tools on investigation of pathogen transmission: Prevention and control

Transmission mechanics of infectious pathogen in various environments are of great complexity and has always been attracting many researchers' attention. As a cost-effective and powerful method, Computational Fluid Dynamics (CFD) plays an important role in numerically solving environmental fluid mechanics. Besides, with the development of computer science, an increasing number of researchers start to analyze pathogen transmission by using CFD methods. Inspired by the impact of COVID-19, this review summarizes research works of pathogen transmission based on CFD methods with different models and algorithms. Defining the pathogen as the particle or gaseous in CFD simulation is a common method and epidemic models are used in some investigations to rise the authenticity of calculation. Although it is not so difficult to describe the physical characteristics of pathogens, how to describe the biological characteristics of it is still a big challenge in the CFD simulation. A series of investigations which analyzed pathogen transmission in different environments (hospital, teaching building, etc) demonstrated the effect of airflow on pathogen transmission and emphasized the importance of reasonable ventilation. Finally, this review presented three advanced methods: LBM method, Porous Media method, and Web-based forecasting method. Although CFD methods mentioned in this review may not alleviate the current pandemic situation, it helps researchers realize the transmission mechanisms of pathogens like viruses and bacteria and provides guidelines for reducing infection risk in epidemic or pandemic situations.

Trajectories of large respiratory droplets in indoor environment: A simplified approach

The recent pandemic of COVID-19 has brought about tremendous impact on every aspect of human activities all over the world. The main route of transmission is believed to be through coronavirus-bearing respiratory droplets. The respiratory droplets have a wide spectrum in droplet size, ranging from very small droplets (aerosol droplets) to large droplets of tens and even hundreds of μm in size. The large droplets are expected to move like projectiles under the action of gravity force, buoyancy force and air resistance. Droplet motion is complicated by droplet evaporation, which reduces droplet size in its trajectory and affects the force acting on it. The present work attempts to determine the trajectories of the large droplets by using a simplified single-droplet approach. It aims at providing a clear physical picture to elucidate the mechanics involved in single droplet motion and the various factors affecting the range. Assuming an indoor environment with an air temperature of 18 °C and relative humidity of 50%, the horizontal rangeL x of large respiratory droplets (diameter 120 μm-200 μm) in common respiratory activities are as follows: Speaking,L x ≈ 0.16 m-0.68 m, coughing,L x ≈ 0.58 m-1.09 m, and sneezing,L x ≈ 1.34 m-2.76 m. For the smaller droplets (diameter < 100 μm), the droplets are reduced to aerosol droplets (≤5 μm) due to evaporation, and will remain suspended in the air instead of falling onto the ground like a projectile.

A Bibliometric Analysis of Corona Pandemic in Social Sciences: A Review of Influential Aspects and Conceptual Structure

Corona pandemic has affected the whole world, and it is a highly researched area in biological sciences. As the current pandemic has affected countries socially and economically, the purpose of this bibliometric analysis is to provide a holistic review of the corona pandemic in the field of social sciences. This study aims to highlight significant, influential aspects, research streams, and themes. We have reviewed 395 journal articles related to coronavirus in the field of social sciences from 2003 to 2020. We have deployed 'biblioshiny' a web-interface of the 'bibliometrix 3.0' package of R-studio to conduct bibliometric analysis and visualization. In the field of social sciences, we have reported influential aspects of coronavirus literature. We have found that the 'Morbidity and Mortality Weekly Report' is the top journal. The core article of coronavirus literature is 'Guidelines for preventing health-care-associated pneumonia'. The most commonly used word, in titles, abstracts, author's keywords, and keywords plus, is 'SARS'. Top affiliation is 'The University of Hong Kong'. Hong Kong is a leading country based on citations, and the USA is on top based on total publications. We have used a conceptual framework to identify potential research streams and themes in coronavirus literature. Four research streams are found by deploying a co-occurrence network. These research streams are 'Social and economic effects of epidemic disease', 'Infectious disease calamities and control', 'Outbreak of COVID 19,' and 'Infectious diseases and the role of international organizations'. Finally, a thematic map is used to provide a holistic understanding by dividing significant themes into basic or transversal, emerging or declining, motor, highly developed, but isolated themes. These themes and subthemes have proposed future directions and critical areas of research.

Covid-19 Airborne Transmission and Its Prevention: Waiting for Evidence or Applying the Precautionary Principle?

Besides the predominant ways of transmission of SARS-CoV-2 (namely, contacts and large droplets) the airborne one is increasingly taken into consideration as a result of latest research findings. Nevertheless, this possibility has been already suggested by previous studies on other coronaviruses including SARS-CoV and MERS-CoV. To describe the state of the art of coronaviruses and airborne transmission, a systematic review was carried out using the PRISMA methodology. Overall, 64 papers were selected and classified into three main groups: laboratory experiments (12 papers), air monitoring (22) and epidemiological and airflow model studies (30). The airborne transmission of SARS-CoV-2 is suggested by the studies of the three groups, but none has yet obtained complete evidence. The sampling and detection methods have not been validated, therefore monitoring results are affected by a possible underestimation. Then, epidemiological investigations only hypothesize the airborne transmission as a possible explanation for some illness cases, but without estimating its attributable risk. Nevertheless, while waiting for more evidence, it is urgent to base advice on preventive measures, such as the use of masks, safe distancing and air ventilation, on the precautionary principle.

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

Single-sided natural ventilation was numerically investigated to determine the impact of buoyancy and wind on the cross-transmission of pollution by considering six window types commonly found in multistory buildings. The goal of this study was to predict the gaseous pollutant transmission using computational fluid dynamics based on the Reynolds-averaged Navier-Stokes equations and baseline k-ω turbulence equations. The results indicated that ventilation rates generally increased with increasing wind speeds if the effects of buoyancy and wind were not suppressed; however, the re-entry ratio representing the proportion of expelled air re-entering other floors and the corresponding risk of infection decreased. If the source of the virus was on a central floor, the risk of infection was the highest on the floors closest to the source. Different window types were also considered for determining their effectiveness in controlling cross-transmission and infection risk, depending on the source location and driving force (e.g., buoyancy and wind).

Numerical investigation of gaseous pollutant cross-transmission for single-sided natural ventilation driven by buoyancy and wind

Single-sided natural ventilation was numerically investigated to determine the impact of buoyancy and wind on the cross-transmission of pollution by considering six window types commonly found in multistory buildings. The goal of this study was to predict the gaseous pollutant transmission using computational fluid dynamics based on the Reynolds-averaged Navier-Stokes equations and baseline k-ω turbulence equations. The results indicated that ventilation rates generally increased with increasing wind speeds if the effects of buoyancy and wind were not suppressed; however, the re-entry ratio representing the proportion of expelled air re-entering other floors and the corresponding risk of infection decreased. If the source of the virus was on a central floor, the risk of infection was the highest on the floors closest to the source. Different window types were also considered for determining their effectiveness in controlling cross-transmission and infection risk, depending on the source location and driving force (e.g., buoyancy and wind).

The impact of building surface temperature rise on airflow and cross-contamination around high-rise building

This paper numerically studies the characteristics of flow field around a high-rise building and the cross-contamination when the building surface is heated by the solar radiation. Firstly, the normalized concentration K_c is used to evaluate the dispersion characteristics under different source locations without surface temperature rise. Under iso-thermal condition, the near-wall pollutant dispersion features revealed by the predicted results are similar to our previous wind tunnel experiment. Then, the effect of wall surface temperature rise on the cross-contamination and the flow fields is evaluated based on the near-wall concentration distributions and the wake zone vortex core positions, respectively. When the building surface temperature rises, the location of vortex core obviously changes comparing with that under iso-thermal condition. The correction formula for the vortex core location with the leeward wall surface temperature rise below 15 K is developed. The windward wall surface temperature rise brings more serious pollutant accumulation. The near-wall concentrations increase with the rise of temperature when the pollutant is released from the bottom and middle of leeward wall surface, while the top-release scenario exhibited a contrary tendency. For the three interval ranges of generally recognized Richardson number Ri (Ri < 0.1; 0.1 < Ri < 10; Ri > 10), these results indicate that when Ri is less than 0.1, the effect of wall surface temperature rise on near-wall flow and cross-contamination of small-scale model cannot be ignored.

Investigation of interunit dispersion in 2D street canyons: A scaled outdoor experiment

Interunit dispersion problems have been studied previously mainly through on-site measurements, wind tunnel tests, and CFD simulations. In this study, a scaled outdoor experiment was conducted to examine the interunit dispersion characteristics in consecutive two-dimensional street canyons. Tracer gas ( C O 2 ) was continuously released to simulate the pollutant dispersion routes between the rooms in street canyons. The wind velocity, wind direction, air temperature, and tracer gas concentrations were monitored simultaneously. Two important parameters, the air exchange rate and reentry ratio, were analyzed to reveal the ventilation performance and interunit dispersion of the rooms in the street canyons. Based on the real-time weather conditions, it was found that the ventilation performance of the source room varied according to the room location. The air exchange rate distribution of the leeward-side room was more stable than that of the windward side. The tracer gas was mainly transported in the vortex direction inside the street canyon, and the highest reentry ratio was observed at the room nearest to the source room along the transportation route. In addition, under real weather conditions, the rooms in the street canyon have a high probability of experiencing a high reentry ratio based on the maximum reentry ratio of each room. This study provides authentic airflow and pollutant dispersion information in the street canyons in an urban environment. The dataset of this experiment can be used to validate further numerical simulations.

Investigation of interunit dispersion in 2D street canyons: A scaled outdoor experiment

Interunit dispersion problems have been studied previously mainly through on-site measurements, wind tunnel tests, and CFD simulations. In this study, a scaled outdoor experiment was conducted to examine the interunit dispersion characteristics in consecutive two-dimensional street canyons. Tracer gas ( C O 2 ) was continuously released to simulate the pollutant dispersion routes between the rooms in street canyons. The wind velocity, wind direction, air temperature, and tracer gas concentrations were monitored simultaneously. Two important parameters, the air exchange rate and reentry ratio, were analyzed to reveal the ventilation performance and interunit dispersion of the rooms in the street canyons. Based on the real-time weather conditions, it was found that the ventilation performance of the source room varied according to the room location. The air exchange rate distribution of the leeward-side room was more stable than that of the windward side. The tracer gas was mainly transported in the vortex direction inside the street canyon, and the highest reentry ratio was observed at the room nearest to the source room along the transportation route. In addition, under real weather conditions, the rooms in the street canyon have a high probability of experiencing a high reentry ratio based on the maximum reentry ratio of each room. This study provides authentic airflow and pollutant dispersion information in the street canyons in an urban environment. The dataset of this experiment can be used to validate further numerical simulations.

Dispersion Characteristics of Hazardous Gas and Exposure Risk Assessment in a Multiroom Building Environment

The leakage of hazardous chemicals during storage and transport processes is a kind of commonly occurring accident that can pose a serious threat to people's lives and property. This paper aims to investigate the airflow and dispersion characteristics of hazardous gas around a multiroom building, and evaluate the corresponding exposure risks. The effects on indoor air quality (IAQ) when polluted air enters a room under different indoor and external conditions were examined by using a computational fluid dynamics technique. First, the numerical model established herein was verified by the available wind-tunnel experimental data, and acceptable agreement was found between the predicted and measured velocities. Subsequently, the effects of different natural ventilation paths, wall porosities and outdoor pollutant source characteristics on the airflow and contaminant distribution were evaluated. The study not only reveals the airflow pattern and concentration distribution in indoor spaces under different natural ventilation conditions but also quantitatively analyzes the relationship between the probability of death and the corresponding source strength under the circumstance of pollutant leakage near a building. The results can be useful for the prevention and control of hazardous chemical gas leakages and provide some guidance on evacuation after an accidental or routine leakage.

A tracing method of airborne bacteria transmission across built environments

Disease transmission across built environments has been found to be a serious health risk. Airborne transmission is a vital route of disease infection caused by bacteria and virus. However, tracing methods of airborne bacteria in both lab and field research failed to veritably express the transporting process of microorganism in the air. A new tracing method of airborne bacteria used for airborne transmission was put forward and demonstrated its feasibility by conducting a field evaluation on the basis of genetic modification and bioaerosol technology. A specific gene fragment (pFPV-mCherry fluorescent protein plasmid) was introduced into nonpathogenic E. coli DH5α as tracer bacteria by high-voltage electroporation. Gel electrophoresis and DNA sequencing proved the success of the synthesis. Genetic stability, effect of aerosolization on the survival rate of tracer bacteria, and the application of the tracer bacteria to the airborne bacteria transmission were examined in both lab and field. Both the introduced plasmid stability rates of tracer E. coli in pre-aerosolization and post-aerosolization were above 95% in five test days. Survival rate of tracer E. coli at 97.5% ± 1.2% through aerosolization was obtained by an air-atomizer operated at an air pressure of 30 Psi. In the field experiment, the airborne transmission of E. coli between poultry houses was proved and emitted E. coli was more easily transmitted into self-house than adjacent house due to the ventilation design and weather condition. Our results suggested that the tracing method of airborne bacteria was available for the investigation of airborne microbial transmission across built environments.

The influence of roadside trees on the diffusion of road traffic pollutants and their magnetic characteristics in a typical semi-arid urban area of Northwest China

Leaf samples of Juniperus formosana were collected from an open road environment, in order to establish how particulate matter (PM) generated by vehicles was dispersed in both horizontal and vertical directions. Sampling was conducted at sites with trees of varying height and configuration adjacent to a major road in Lanzhou, Gansu Province, Northwest China. The concentration of remanence-bearing ferrimagnets in the leaf samples was estimated from measurements of Saturation Isothermal Remanent Magnetization (SIRM), while the weight of particles deposited on the leaves and their elemental composition were determined at different heights and in different directions relative to the road. The PM on the surface of needles was predominantly influenced by traffic emissions and by dust resuspension. Rows of roadside trees, as opposed to solitary trees, were more effective at intercepting PM and thus in filtering road traffic pollution. The results indicate that Juniperus formosana needles may be an effective bio-sensor for monitoring variations in the spatial diffusion of road pollutants.

The influence of envelope features on interunit dispersion around a naturally ventilated multi-story building

This study examines the influence of building envelope features on interunit dispersion around multi-story buildings, when the presence of an upstream interfering building is also considered. Validated CFD methods in the steady-state RANS framework are employed. In general, the reentry ratios of pollutant from a source unit to adjacent units are mostly in the order of 0.1%, but there are still many cases being in the order of 1%. The influence of envelope features is dependent strongly on the interaction between local wind direction and envelope feature. In a downward dominated near-facade flow field, the presence of vertical envelope features forms dispersion channels to intensify the unidirectional spread. Horizontal envelope features help induce the dilution of pollutant to the main stream and weakens largely the vertical interunit dispersion. The large influences caused by the presence of envelope features extend the existing understanding of interunit dispersion based on flat-facade buildings.

CFD investigation on the effects of wind and thermal wall-flow on pollutant transmission in a high-rise building

The solar radiation can heat the building outer surface, and then cause the upward natural convection flows adjacent to the wall. This phenomenon is especially obvious on a windless sunny day. The near wall thermal plume can drive gaseous pollutants released from lower floors to upper floors. Combined with the effect of ambient approaching wind, the transmission routes will be very complicated. The paper aims to investigate the airflow patterns and pollutant transmission within a building under the effects of wind and thermal forces. A hypothetical twenty-storey slab-shape high-rise building in Shanghai with single-sided natural ventilation is set as the research object in the present study. The intensity of solar radiation on a typical day during transition season is theoretically analysed. The temperature difference between the heated building envelope and the ambient air is calculated by a simplified heat balance model. Finally, the tracer gas method is employed in the numerical simulation to analyse the influence of the wind and wall thermal plume flow on the inter-flat pollutant transmission characteristics. The results show that, the temperature difference between sunward and shady side wall is about 10 K at noon on the designate day. When the source is set as a point with steady intensity and the buoyancy is stronger than or approximately equivalent to the wind, the reentry ratio of the flat immediately above the source can be around 25%.

Gaseous pollutant transmission through windows between vertical floors in a multistory building with natural ventilation

Natural ventilation is an effective strategy to control thermal comfort in buildings, and can be enhanced depending on the window style. The combination of natural ventilation and window can also facilitate the removal or dilution of gaseous pollutants from indoor sources in newly decorated buildings. However, the windows on the same facade may cause gaseous pollutant cross-transmission during single-sided natural ventilation between households on different floors close to the source. Although some research has focused on the pollutant cross-transmission in buildings, the simplification of windows into rectangular openings often affects accurate knowledge of pollutant transmission characteristics. Therefore, this investigation explored gaseous pollutant cross-transmission through real windows during single-sided, buoyancy-driven ventilation in a multistory building. Six types of windows were modeled for the indoor pollutant of gaseous formaldehyde (HCHO). Computational fluid dynamics (CFD) was utilized to solve characteristics of pollutant transmission inside and outside the multistory building. The results indicated that the ventilation rates, thermal profiles and pollutant transmission inside and outside the building varied for each window type, although the open window areas were identical. The re-entry ratio of exhausted air entering upper floors and the infection risk of epidemic viruses caused by airborne cross-transmission was sensitive to ventilation rates and window configurations, while the sensitivities for window configurations varied case by case. The comparisons also revealed that the specification of ambient temperature and pollutant release rate ultimately did not affect the evaluation of pollutant cross-transmission using CFD.

Air infiltration induced inter-unit dispersion and infectious risk assessment in a high-rise residential building

Identifying possible airborne transmission routes and assessing the associated infectious risks are essential for implementing effective control measures. This study focuses on the infiltration-induced inter-unit pollutant dispersion in a high-rise residential (HRR) building. The outdoor wind pressure distribution on the building facades was obtained from the wind tunnel experiments. And the inter-household infiltration and tracer gas transmission were simulated using multi-zone model. The risk levels along building height and under different wind directions were examined, and influence of component leakage area was analysed. It is found that, the cross-infection risk can be over 20% because of the low air infiltration rate below 0.7 ACH, which is significantly higher than the risk of 9% obtained in our previous on-site measurement with air change rate over 3 ACH. As the air infiltration rate increases along building height, cross-infection risk is generally higher on the lower floors. The effect of wind direction on inter-unit dispersion level is significant, and the presence of a contaminant source in the windward side results in the highest cross-infection risks in other adjacent units on the same floor. Properly improving internal components tightness and increasing air change via external components are beneficial to the control of internal inter-unit transmission induced by infiltration. However, this approach may increase the cross-infection via the external transmission, and effective control measures should be further explored considering multiple transmission routes.

Wind tunnel tests of inter-flat pollutant transmission characteristics in a rectangular multi-storey residential building, part B: Effect of source location

The pollutant behavior in and around a naturally ventilated building requires to be investigated quantitatively as the growing concern on air quality within the built environment. The objective of the present study is to further investigate the wind induced inter-flat pollutant transmission and cross contamination routes in typical buildings in Shanghai. In this paper, a set of experiments was carried out in a boundary layer wind tunnel using a 1:30 reduced scale model that represented the typical configuration of rectangular multi-storey residential buildings. Sulfur hexafluoride (SF6) was employed as a tracer gas in the wind tunnel tests. Two natural ventilation modes, single-sided ventilation and cross ventilation were considered. The conditions under prevailing wind direction with different source locations on the windward side were compared. The pressure coefficients on all of the building façades and tracer gas concentration distributions were monitored and analysed. The experimental results elucidated that contaminant released from windward units could spread vertically and horizontally to other units on the source façade and downstream units. The source location was a significant influence factor on the pollutant concentration in various units. In the single-sided ventilated building, the infected risks of leeward units were even higher than those in some windward units. In the cross ventilated building, the vertical transmission could be suppressed and the horizontal transmission was reinforced. The study is helpful for further understanding of the inter-flat airborne transmission within an isolated building.

The influence of street layouts and viaduct settings on daily carbon monoxide exposure and intake fraction in idealized urban canyons

Environmental concerns have been raised on the adverse health effects of vehicle emissions in micro-scale traffic-crowded street canyons, especially for pedestrians and residents living in near-road buildings. Viaduct design is sometimes used to improve transportation efficiency but possibly affects urban airflow and the resultant exposure risk, which have been rarely investigated so far. The personal intake fraction (P_IF) is defined as the average fraction of total emissions that is inhaled by each person of a population (1 ppm = 1 × 10^-6), and the daily carbon monoxide (CO) pollutant exposure (E_t) is estimated by multiplying the average concentration of a specific micro-environment within one day. As a novelty, by considering time activity patterns and breathing rates in various micro-environments for three age groups, this paper introduces IF and E_t into computational fluid dynamic (CFD) simulation to quantify the impacts of street layouts (street width/building height W/H = 1, 1.5, 2), source location, viaduct settings and noise barriers on the source-exposure correlation when realistic CO sources are defined. Narrower streets experience larger P_IF (1.51-5.21 ppm) and CO exposure, and leeward-side buildings always attain higher vehicular pollutant exposure than windward-side. Cases with a viaduct experience smaller P_IF (3.25-1.46 ppm) than cases without a viaduct (P_IF = 5.21-2.23 ppm) if the single ground-level CO source is elevated onto the viaduct. With two CO sources (both ground-level and viaduct-level), daily CO exposure rises 2.80-3.33 times but P_IF only change slightly. Noise barriers above a viaduct raise concentration between barriers, but slightly reduce vehicular exposure in near-road buildings. Because people spend most of their time indoors, vehicular pollutant exposure within near-road buildings can be 6-9 times that at pedestrian level. Although further studies are still required to provide practical guidelines, this paper provides effective methodologies to quantify the impacts of street/viaduct configurations on human exposure for urban design purpose.

Wind tunnel tests of inter-flat pollutant transmission characteristics in a rectangular multi-storey residential building, part A: Effect of wind direction

The inter-flat dispersion of hazardous air pollutants in residential built environment has become a growing concern, especially in crowed urban areas. The purpose of present study is to investigate the wind induced air pollutant transmission and cross contamination routes in typical buildings. In this paper, a series of experiments was carried out in a boundary layer wind tunnel using a 1:30 scaled model that represented the typical configuration of rectangular multi-storey residential buildings in Shanghai. Sulfur hexafluoride (SF₆) was employed as tracer gas in the wind tunnel tests. The conditions under two ventilation modes, i.e. single-sided natural ventilation and cross natural ventilation, were compared. The tracer gas concentration distributions under four approaching wind angles were monitored and analyzed. Computational Fluid Dynamics (CFD) method was adopted to assist in analyzing airflow patterns. The experiment results elucidated that in the two ventilation scenarios, both of the vertical and horizontal inter-flat airborne transmission could proceed. The wind direction played a key role on the pollutant concentration distribution. Compared with the single-sided ventilation mode, cross ventilation could weaken the air pollutant dispersion along the vertical direction when the contamination source was on the windward or on the leeward unit. When the wind blowing parallelly to the source unit window, namely the source room was on the sideward, cross ventilation would not suppress the vertical transport on one hand, but reinforce the horizontal transmission on the other hand. The study is helpful for the analysis of infection risk of respiratory diseases in the residential buildings.

Wind tunnel tests of inter-flat pollutant transmission characteristics in a rectangular multi-storey residential building, part A: Effect of wind direction

The inter-flat dispersion of hazardous air pollutants in residential built environment has become a growing concern, especially in crowed urban areas. The purpose of present study is to investigate the wind induced air pollutant transmission and cross contamination routes in typical buildings. In this paper, a series of experiments was carried out in a boundary layer wind tunnel using a 1:30 scaled model that represented the typical configuration of rectangular multi-storey residential buildings in Shanghai. Sulfur hexafluoride (SF₆) was employed as tracer gas in the wind tunnel tests. The conditions under two ventilation modes, i.e. single-sided natural ventilation and cross natural ventilation, were compared. The tracer gas concentration distributions under four approaching wind angles were monitored and analyzed. Computational Fluid Dynamics (CFD) method was adopted to assist in analyzing airflow patterns. The experiment results elucidated that in the two ventilation scenarios, both of the vertical and horizontal inter-flat airborne transmission could proceed. The wind direction played a key role on the pollutant concentration distribution. Compared with the single-sided ventilation mode, cross ventilation could weaken the air pollutant dispersion along the vertical direction when the contamination source was on the windward or on the leeward unit. When the wind blowing parallelly to the source unit window, namely the source room was on the sideward, cross ventilation would not suppress the vertical transport on one hand, but reinforce the horizontal transmission on the other hand. The study is helpful for the analysis of infection risk of respiratory diseases in the residential buildings.

On-site measurement of tracer gas transmission between horizontal adjacent flats in residential building and cross-infection risk assessment

Airborne transmission is a main spread mode of respiratory infectious diseases, whose frequent epidemic has brought serious social burden. Identifying possible routes of the airborne transmission and predicting the potential infection risk are meaningful for infectious disease control. In the present study, an internal spread route between horizontal adjacent flats induced by air infiltration was investigated. On-site measurements were conducted, and tracer gas technique was employed. Two measurement scenarios, closed window mode and open window mode, were compared. Using the calculated air change rate and mass fraction, the cross-infection risk was estimated using the Wells-Riley model. It found that tracer gas concentrations in receptor rooms are one order lower than the source room, and the infection risks are also one order lower. Opening windows results in larger air change rate on the one hand, but higher mass fraction on the other hand. Higher mass fraction not necessarily results in higher infection risk as the pathogen concentration in the source room is reduced by the higher air change rate. In the present study, opening windows could significantly reduce the infection risk of the index room but slightly reduce the risks in receptor rooms. The mass fraction of air originated from the index room to the receptor units could be 0.28 and the relative cross-infection risk through the internal transmission route could be 9%, which are higher than the external spread through single-sided window flush. The study implicates that the horizontal transmission route induced by air infiltration should not be underestimated.

Large eddy simulation of wind-induced interunit dispersion around multistory buildings

Previous studies regarding interunit dispersion used Reynolds-averaged Navier-Stokes (RANS) models and thus obtained only mean dispersion routes and re-entry ratios. Given that the envelope flow around a building is highly fluctuating, mean values could be insufficient to describe interunit dispersion. This study investigates the wind-induced interunit dispersion around multistory buildings using the large eddy simulation (LES) method. This is the first time interunit dispersion has been investigated transiently using a LES model. The quality of the selected LES model is seriously assured through both experimental validation and sensitivity analyses. Two aspects are paid special attention: (i) comparison of dispersion routes with those provided by previous RANS simulations and (ii) comparison of timescales with those of natural ventilation and the survival times of pathogens. The LES results reveal larger dispersion scopes than the RANS results. Such larger scopes could be caused by the fluctuating and stochastic nature of envelope flows, which, however, is canceled out by the inherent Reynolds-averaged treatment of RANS models. The timescales of interunit dispersion are comparable with those of natural ventilation. They are much shorter than the survival time of most pathogens under ordinary physical environments, indicating that interunit dispersion is a valid route for disease transmission.

Large eddy simulation of wind-induced interunit dispersion around multistory buildings

Previous studies regarding interunit dispersion used Reynolds-averaged Navier-Stokes (RANS) models and thus obtained only mean dispersion routes and re-entry ratios. Given that the envelope flow around a building is highly fluctuating, mean values could be insufficient to describe interunit dispersion. This study investigates the wind-induced interunit dispersion around multistory buildings using the large eddy simulation (LES) method. This is the first time interunit dispersion has been investigated transiently using a LES model. The quality of the selected LES model is seriously assured through both experimental validation and sensitivity analyses. Two aspects are paid special attention: (i) comparison of dispersion routes with those provided by previous RANS simulations and (ii) comparison of timescales with those of natural ventilation and the survival times of pathogens. The LES results reveal larger dispersion scopes than the RANS results. Such larger scopes could be caused by the fluctuating and stochastic nature of envelope flows, which, however, is canceled out by the inherent Reynolds-averaged treatment of RANS models. The timescales of interunit dispersion are comparable with those of natural ventilation. They are much shorter than the survival time of most pathogens under ordinary physical environments, indicating that interunit dispersion is a valid route for disease transmission.

CFD simulation of the effect of an upstream building on the inter-unit dispersion in a multi-story building in two wind directions

Previous studies on inter-unit dispersion are limited to isolated buildings. The influence of an upstream interfering building may significantly modify the indoor airflow characteristics of the wind-induced natural ventilated downstream interfered building. Motivated by the findings in previous studies, namely that infectious respiratory aerosols exhausted from a unit can re-enter into another unit in the same building through building envelope openings, this study investigates the inter-unit pollutant dispersion around a multi-story building in two wind directions by employing the computational fluid dynamics (CFD) method. The CFD model employed in this study has been validated against previous experimental data. The results show that the presence of an upstream building greatly changes the path lines around the downstream target building and the pollutant transportation routes around it. The presence of a low upstream building also greatly increases the average air exchange rate (ACH) values and the pollutant re-entry ratios (R_k) below the source unit on the windward side of the downstream target building for normal wind incidence. However, the presence of a high upstream building greatly increases the average ACH values on the windward side and increases the R_k on the leeward side of the downstream building for oblique wind incidence.

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Interunit pollutant dispersion in a naturally ventilated building was investigated.

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Effect of an upstream interfering building on the target building was examined.

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A high and a low upstream buildings were considered.

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An upstream building improves ventilation performance of the target building.

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An upstream building enhances Interunit dispersion in the target building.

Atmospheric dispersion modelling of bioaerosols that are pathogenic to humans and livestock - A review to inform risk assessment studies

In this review we discuss studies that applied atmospheric dispersion models (ADM) to bioaerosols that are pathogenic to humans and livestock in the context of risk assessment studies. Traditionally, ADMs have been developed to describe the atmospheric transport of chemical pollutants, radioactive matter, dust, and particulate matter. However, they have also enabled researchers to simulate bioaerosol dispersion. To inform risk assessment, the aims of this review were fourfold, namely (1) to describe the most important physical processes related to ADMs and pathogen transport, (2) to discuss studies that focused on the application of ADMs to pathogenic bioaerosols, (3) to discuss emission and inactivation rate parameterisations, and (4) to discuss methods for conversion of concentrations to infection probabilities (concerning quantitative microbial risk assessment). The studies included human, livestock, and industrial sources. Important factors for dispersion included wind speed, atmospheric stability, topographic effects, and deposition. Inactivation was mainly governed by humidity, temperature, and ultraviolet radiation. A majority of the reviewed studies, however, lacked quantitative analyses and application of full quantitative microbial risk assessments (QMRA). Qualitative conclusions based on geographical dispersion maps and threshold doses were encountered frequently. Thus, to improve risk assessment for future outbreaks and releases, we recommended determining well-quantified emission and inactivation rates and applying dosimetry and dose-response models to estimate infection probabilities in the population at risk.

The airborne transmission of infection between flats in high-rise residential buildings: A review

The inter-flat airborne cross-transmission driven by single-sided natural ventilation has been identified recently in high-rise residential buildings, where most people live now in densely populated areas, and is one of the most complex and least understood transport routes. Given potential risks of infection during the outbreak of severe infectious diseases, the need for a full understanding of its mechanism and protective measures within the field of epidemiology and engineering becomes pressing. This review paper considers progress achieved in existing studies of the concerned issue regarding different research priorities. Considerable progress in observing and modeling the inter-flat transmission and dispersion under either buoyancy- or wind-dominated conditions has been made, while fully understanding the combined buoyancy and wind effects is not yet possible. Many methods, including on-site measurements, wind tunnel tests and numerical simulations, have contributed to the research development, despite some deficiencies of each method. Although the inter-flat transmission and dispersion characteristics can be demonstrated and quantified in a time-averaged sense to some extent, there are still unanswered questions at a fundamental level about transient dispersion process and thermal boundary conditions, calling for further studies with more advanced models for simulations and more sound experiments for validations.

The airborne transmission of infection between flats in high-rise residential buildings: A review

The inter-flat airborne cross-transmission driven by single-sided natural ventilation has been identified recently in high-rise residential buildings, where most people live now in densely populated areas, and is one of the most complex and least understood transport routes. Given potential risks of infection during the outbreak of severe infectious diseases, the need for a full understanding of its mechanism and protective measures within the field of epidemiology and engineering becomes pressing. This review paper considers progress achieved in existing studies of the concerned issue regarding different research priorities. Considerable progress in observing and modeling the inter-flat transmission and dispersion under either buoyancy- or wind-dominated conditions has been made, while fully understanding the combined buoyancy and wind effects is not yet possible. Many methods, including on-site measurements, wind tunnel tests and numerical simulations, have contributed to the research development, despite some deficiencies of each method. Although the inter-flat transmission and dispersion characteristics can be demonstrated and quantified in a time-averaged sense to some extent, there are still unanswered questions at a fundamental level about transient dispersion process and thermal boundary conditions, calling for further studies with more advanced models for simulations and more sound experiments for validations.

The influence of human walking on the flow and airborne transmission in a six-bed isolation room: Tracer gas simulation

By performing unsteady CFD simulations using RNG k-ɛ model and dynamic mesh technique, this paper investigates how the walking motion of health care worker (HCW) influences gaseous dispersion in a six-bed isolation room with nine downward supplies and six ceiling-level or floor-level exhausts. The flow near and behind HCW is easily affected by HCW motion. The flow disturbance induced by HCW walking with swinging arms and legs is a mixing process. The walking HCW displaces air in front of it and carries air in the wake forwardly, meanwhile pressure difference drives air from two lateral sides into the wake. HCW motion (0-5.4 s) indeed induces a little gaseous dispersion, but the residual flow disturbance after HCW stops (5.4 s-25.4 s) induces more gaseous agent spread and it requires more than 30-60 s to approximately recover to the initial state after HCW stops. Although HCW motion indeed affects airborne transmission, but its effect is less important than ventilation design. No matter with or without HCW motion, the ceiling-level exhausts perform much better in controlling airborne transmission than the floor-level exhausts with the same air change rate (12.9 ACH). Smaller air change rate of 6 ACH experiences higher concentration and more gaseous spread than 12.9 ACH. In contrast to the realistic human walking, the simplified motion of a rectangular block produces stronger flow disturbance. Finally surface heating of HCW produces a stronger thermal body plume and enhances turbulence near HCW, thus slightly strengthens airborne transmission.

Numerical investigation of wind-induced airflow and interunit dispersion characteristics in multistory residential buildings

Compared with the buoyancy-dominated upward spread, the interunit dispersion of pollutants in wind-dominated conditions is expected to be more complex and multiple. The aim of this study is to investigate the wind-induced airflow and interunit pollutant dispersion in typical multistory residential buildings using computational fluid dynamics. The mathematical model used is the nonstandard k-ε model incorporated with a two-layer near-wall modification, which is validated against experiments of previous investigators. Using tracer gas technique, the reentry of exhaust air from each distinct unit to other units on the same building, under different practical conditions, is quantified, and then, the possible dispersion routes are revealed. The units on the floor immediately below the source on the windward side, and vertically above it on the leeward side, where the reentry ratios are up to 4.8% and 14.9%, respectively, should be included on the high-infection list. It is also found that the presence of balconies results in a more turbulent near-wall flow field, which in turn significantly changes the reentry characteristics. Comparison of the dispersion characteristics of the slab-like building and the more complicated building in cross (#) floorplan concludes that distinctive infectious control measures should be implemented in these two types of buildings.

Interdisciplinary approaches to zoonotic disease

Zoonotic infections are on the increase worldwide, but most research into the biological, environmental and life science aspects of these infections has been conducted in separation. In this review we bring together contemporary research in these areas to suggest a new, symbiotic framework which recognises the interaction of biological, economic, psychological, and natural and built environmental drivers in zoonotic infection and transmission. In doing so, we propose that some contemporary debates in zoonotic research could be resolved using an expanded framework which explicitly takes into account the combination of motivated and habitual human behaviour, environmental and biological constraints, and their interactions.

Predictions and measurements of the stack effect on indoor airborne virus transmission in a high-rise hospital building

As the viral diseases such as Severe Acute Respiratory Syndrome (SARS) and Influenza A (H1N1) occur in many countries recently, the epidemic of those influenza viruses causes many human casualties. Moreover, the second infection from infected patients particularly within general hospitals frequently takes places due to improperly hospitalized and/or quarantined patients. Accordingly, it becomes a great concern to accommodate safer ventilation system in general hospital wards against such airborne transmitted viruses. It is also a recent trend that many urban general hospitals are designed and constructed as high-rises. If a virus is transmitted through uncontrolled air movement within a hospital and then infected other patients or healthy visitors, it might be impossible to control the spread of the disease. Thus research has been preceded scrutinizing stack effect on the indoor airborne virus transmission in large hospitals by conducting both the field measurement and numerical analysis according to the outdoor temperature and the releasing vertical points of the tracer gas assumed as a viral contaminant. In the field measurement of a high-rise hospital, the indoor airflow was affected by the stack effect of vertical chute of the building. The numerical simulation was verified by comparing its prediction results and the field measurement data. In result, very high possibility has witnessed that the airborne contaminant emitted from the infected patients in the lower floors could be transported to the higher floors through the airflow driven by the stack effect.