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Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities
Abstract
A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm−3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm−3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm−3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm−3 for breathing to 1.1 cm−3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.
... The amount of pathogen inhaled by a susceptible individual may be estimated from the well-mixed model [29,31,33,34]. Consider the scenario of a sick person entering a room of volume and ejecting virus-laden droplet nuclei at a steady rate of ( ) nuclei per second into the room. ...
... In Fig. 3B we plot the long-time value of the correction function ∞ versus for Room 0 (dashed curves) and Room 1a (solid curves) and for various types of expiratory events (breathing, singing, etc.). We note that the ejected droplet spectra for different expiratory activities were obtained from the experimental work of [34]. A value of ∞ = 2 for = 1 m, for example, implies that on average, and after sufficiently long time, nuclei concentration is twice the value predicted by the wellmixed model at locations that are = 1 m away from the source. ...
... The proton transfer between AH 2 and (H 2 O)10 .OHcluster takes place through proton transfer to OHion of the cluster involving H-bonding interactions with three water molecules [see SI]. The resulting AH -.(H 2 O)11 complex is stable with -49.3 kcal/mol enthalpy. The proton transfer in the absence of OHion did not lead to AH -+ H 3 O + dissociation products. ...
... This is 7.9 kcal/mol more exothermic than the proton transfer reaction on the surface without the presence of O 3 . Further, two water molecules and OH-ion are involved in this proton transfer reaction, which may result in negligible kinetic barrier for the formation of stable [AH -.(H 2 O)11 .O 3 ] complex. The reaction of AHwith O 3 on the water surface results in proton exchange leading to dehydroxy ascorbic acid (DHA) along with singlet oxygen and hydroxide ion. ...
The present study investigates the effects of air pollution and climate factors on the acceleration of SARS-CoV-2 transmission and mortality. In particular, the correlations between O3, NO2, PM2.5, PM10 and SO2 concentrations with daily number of infections and fatalities caused by the second wave of COVID-19 during the time period March–June 2021 in Indian cities with different climate zones are analyzed. The chemical transformations in the atmosphere that translated to dispersion of SARS-CoV-2 aerosols and their deposition in the respiratory system are studied. The results suggested that exposure to a higher level of O3 may weaken the respiratory system, and therefore resistance against COVID-19 is suppressed. The infectious aerosols undergo reactive encounters with atmospheric oxidants, forming secondary aerosols before deposition in the lungs. The pulmonary epithelium is naturally protected against atmospheric O3 and secondary aerosols by lung-lining fluids that contain ascorbic acid, AH2 and other antioxidants. Since O3 and COVID-19 infections showed a positive correlation, AH2 and the underlying tissues will be the most affected. The mechanism for the interaction of O3 with AH2 is studied using quantum chemical methods. During this interaction, a persistent ozonide is formed in lung-lining fluids and this is acidified by the inhaled aerosols. Earlier epidemiological and toxicological studies revealed that this ozonide leads to the formation of cytotoxic free radicals that can cause oxidative stress during breathing. Thus, O3 plays a significant role in the deposition of aerosols in the lungs. The results of this study add to prevailing evidence as well as providing new insights into the role of ambient O3 in the dispersion and deposition of SARS-CoV-2 aerosols.
... Human activities, especially respiratory activities have been approved to be efficient aerosol-generating procedures : speaking, breathing, coughing, and sneezing can create aerosols originating from the sites of the oral cavity, alveoli, bronchiole, bronchus, and larynx (Xu et al., 2022), with the film breakage and surface shearing considered as the two major mechanisms of aerosol generation (Morawska et al., 2009;Johnson et al., 2011;Abkarian and Stone, 2020;Hamed et al., 2020;Guo et al., 2021;Xu et al., 2022). As a reasonable comparison (Table 1), we tend to believe that swallowing and tongue movements (stretching and slapping) are the major aerosol-generating actions during drinking or eating. ...
... In the shear-induced mechanism of bio-aerosol generation, the passage of high-velocity air stream over the mucus surface will generate wave-like disturbances which lead to aerosol creation. The velocity of airflow during normal breath was reported to be insufficient to generate shear-induced aerosols (Morawska et al., 2009;Scheuch, 2020;Xu et al., 2022), and hence the shear-induced mechanism may not be essential during the oral actions of food consumption (Ni et al., 2015). However, the expiratory airflow immediately after the completion of swallowing (Brodsky et al., 2009;Steele, 2015;Hopkins-Rossabi et al., 2019) has the potential to generate shear-induced aerosols, due to its high velocity. ...
While accumulating evidence implied the involvement of retro-nasal sensation in the consumption of non-volatile taste compounds, it is still unclear whether it was caused by the taste compounds themselves, and if so, how can they migrate from the oral to nasal cavity. At first, we proposed aerosol particles as an alternative oral-nasal mass transfer mechanism. The high-speed camera approved that aerosol particles could be generated by the typical oral and pharynx actions during food oral processing; while the narrow-band imaging of nasal cleft and mass spectrometry of nostril-exhaled air approved the migration of aerosol within the oral-nasal route. Then, the "smelling" of taste compounds within the aerosol particles was testified. The four forced-alternative choices (4AFC) approved that the potential volatile residues or contaminants within the headspace air of pure taste solution cannot arouse significant smell, while the taste compounds embedded in the in-vitro prepared aerosol particles can be "smelled" via the ortho route. The "smell" of sucrose is very different from its taste and the "smell" of quinine, implying its actual olfaction. The sweetness intensity of sucrose solution was also reduced when the volunteers' noses were clipped, indicating the involvement of retro-nasal sensation during its drinking. At last, the efficiency of aerosol as a mechanism of oral-nasal mass transfer was demonstrated to be comparable with the volatile molecules under the experimental condition, giving it the potential to be a substantial and unique source of retro-nasal sensation during food oral processing.
... The talking rate of each human was set to 0.45 l/s. This boundary condition was based on work conducted by Gupta et al. [41] and Morawska et al. [42]. The mean size of the droplet particle was 2.8 µm, and the area of the mouth opening during speech was set to 1.9 cm 2 . ...
... A Gaussian distribution was selected for modeling the particle size, with a mean of 2.8 µm and a standard deviation σ of 0.5 µm. This distribution was selected based on the methodology developed and used from previous works [38,42]. The size of the droplets ranged from 0.46 µm to 4.9 µm, covering both aerosols and droplets in the study. ...
Mitigating the rise and spread of contaminants is a major challenge faced during any contagious disease outbreak. In densely occupied areas, such as a breakroom, the risk of cross-contamination between healthy and infected individuals is significantly higher, thereby increasing the risk of further spread of infectious diseases. In this study, a high fidelity transient fluid solver and Lagrangian particle-based method were used to predict the airflow distribution and contaminant transmission inside a detailed 3D virtual twin of an emergency hospital breakroom. The solver efficiently captured the contaminants emitted simultaneously from multiple talking occupants as well as their propagation inside the breakroom. The influence of airflow distribution on the aerosol spread inside the breakroom for two different air conditioning vent positions was demonstrated with all occupants and with reduced occupants. The baseline simulation with all occupants in the breakroom showed a higher risk of contamination overall as well as between adjacent occupants. It was observed that there was a 26% reduction in the contaminants received by the occupants with the proposed modified vent arrangement and a 70% reduction with the scenarios considering a reduced number of occupants. Furthermore, the fomite deposition and cross-contamination between adjacent humans significantly changed with different ventilation layouts. Based on the simulation results, areas with higher contaminant concentrations were identified, providing information for the positioning of UV lights in the breakroom to efficiently eliminate/reduce the contaminants.
... (2) Only aerosol transmission with particle size below 10 μm was considered for the infection risk assessment. Considering four sizes of particle, i.e., 0.8 μm, 1.8 μm, 3.5 μm, and 5.5 μm [56,57]. ...
... C b is the virus concentration expelled by the cough of infector (copies/m 3 ), the particle concentrations of the four particle sizes were 0.084 cm − 3 (0.8 μm), 0.009 cm − 3 (1.8 μm), 0.003 cm − 3 (3.5 μm), and 0.002 cm − 3 (5.5 μm) [57]. The fine droplets with a diameter below 10 μm have a viral load of 2.08 × 10 6 RNA copies/ml [60]. ...
Aerosol transmission is a route of contagion. The engineering field predicts risk in indoor environment by simulating the airborne transmission of the virus. However, occupant behavior is one of the main causes for the gap between predicted and actual airborne virus transmission risk. To improve the accuracy of transmission risk assessment, this study presents a framework for real-time assessment of infection risk based on the behavioral trajectory of the occupants captured by cameras. The study focused on analyzing the impact of short-range exposure and long-range exposure of occupants on the infection risk through fine-grained trajectories. On-site measurements were conducted in a university office building to obtain the air change rates (ACH) and occupant contact time respectively. A numerical model for quantifying the exposure risk of the two contact routes was also developed. The results demonstrated that the individual movement is diverse. The infection risk varies with the occupied space, behavioral patterns, and exposure time. The main passages and seats in the room, corridor corners, and room doorways are areas of the high frequency of short-range contact. The fraction of long-range exposure is 57.2%, indicating long-range exposure is the dominant route for the limited scenarios and population in this study. The cumulative risk of infection was 0.021 for teachers; 0.029 for employees; and 0.045 for students, with assumptions of initial infection rates of 5%. It can provide real-time warning for occupants through on-site monitoring and contribute to the transmission control and source tracing of airborne viruses.
... There have been a lot of research work on human breath, speech, cough and sneeze droplets size measurement. High variability in measured size distribution of such droplets have been found in literature (Bourouiba 2020(Bourouiba , 2021Stadnytskyi et al. 2020;Morawska et al. 2009;Papineni and Rosenthal 1997). The expired droplets from sneezes or coughs have a counting peak in 2-4 μm in size distribution (with falling height of 5 ft) (Duguid 1946). ...
... It has been shown that, for human speech droplets, the evaporation to the equilibrium droplet size occurs within 0.8 second (De Oliveira et al. 2021;Redrow et al. 2011;Morawska et al. 2009). ...
The size of human speech or cough droplets decides their air-borne transport distance, life span and virus infection risk. We have investigated the measurement accuracy of artificial saliva and saline droplet size for more effective COVID-19 infection control. A spray generator was used for polydisperse droplet generation and a special test chamber was designed for droplet measurement. Saline and artificial saliva were gravimetrically prepared and used to generate droplets. The droplet spray generator and the test chamber were circulated among four metrology institutes (NMC, CMS/ITRI, NIM and KRISS) for droplet size measurement and evaluation of deviations. The composition of artificial saliva was determined by measuring the mass fraction of the inorganic ions. The density of dried artificial saliva droplets was estimated using its composition and the density of each non-volatile component. The volume equivalent diameter (VED) of droplets have been measured by aerodynamic particle sizer (APS) and optical particle size spectrometer (OPSS). As a response to the COVID-19 pandemic, this is the first time that a comparative study among four metrology institutes has been conducted to evaluate the accuracy of saliva and saline droplet size measurement. For artificial saliva droplets measured by OPSS, the deviations from the reference VED (~ 4 μm) were below 5.3%. For saline droplets measured by APS, the deviations from the reference VED were below 10.0%. The potential droplet size measurement errors have been discussed. This work underscores the need for new reference size standards to improve the accuracy and establish traceability in saliva and saline droplet size measurement.
... Therefore, the transport, deposition, and resuspension dynamics of viruses are governed by the properties of the carrier particles. The size distribution and composition of respiratory viral aerosol emissions have been well characterized [5,[20][21][22][23], but characterization of the carrier particles for resuspended viruses has not been reported in the literature. ...
... The APS sample time was set to 1 min. Given the experimental conditions, the liquid particles would be expected to reach equilibrium by the time they are measured by the APS [20]. The PurpleAir LCPMs use optical sensors to estimate PM 1 , PM 2.5 , and PM 10 with a sampling time of approximately 1 min. ...
Many respiratory viruses, including influenza and SARS-CoV-2, are transmitted via the emission and inhalation of infectious respiratory aerosols in indoor environments. Resuspended particles from indoor surfaces and clothing can be a major source of airborne microbiological contaminants in indoor environments; however, it is unknown whether resuspended viruses contribute substantially to disease transmission. In this study, we investigated the resuspension via human walking activity of influenza A virus H3N2 laboratory strain, which was generated through a nebulizer into a sealed, unventilated biosafety level 2 (BSL-2) laboratory. The mean airborne viral concentrations following the resuspension events (3.7×103 viral RNA copies m−3) were two orders of magnitude lower than those following direct emission via the nebulizer (1.1×105 viral RNA copies m−3). The calculated resuspension emission factor (normalized ratio of the airborne mass to mass available for resuspension on the surface) of 10−3 was similar to reported values for 1–2 μm particles. Thus, depending on the infectious dose and viability of the virus, resuspension of settled respiratory viruses could lead to transmission, but the risk appears to be much lower than for direct respiratory emissions. To our knowledge, this is the first full-scale experimental study designed to quantify virus resuspension.
... There have been a lot of research work on human breath, speech, cough and sneeze droplets size measurement. High variability in measured size distribution of such droplets have been found in literature (Bourouiba 2020(Bourouiba , 2021Stadnytskyi et al. 2020;Morawska et al. 2009;Papineni and Rosenthal 1997). The expired droplets from sneezes or coughs have a counting peak in 2-4 μm in size distribution (with falling height of 5 ft) (Duguid 1946). ...
... It has been shown that, for human speech droplets, the evaporation to the equilibrium droplet size occurs within 0.8 second (De Oliveira et al. 2021;Redrow et al. 2011;Morawska et al. 2009). ...
The size of human speech or cough droplets decides their air-borne transport distance, life span and virus infection risk. We have investigated the measurement accuracy of artificial saliva and saline droplet size for more effective COVID-19 infection control. A spray generator was used for polydisperse droplet generation and a special test chamber was designed for droplet measurement. Saline and artificial saliva were gravimetrically prepared and used to generate droplets. The droplet spray generator and test chamber were circulated as travelling standard among four metrology institutes (NMC, CMS/ITRI, NIM and KRISS) for droplet size measurement comparison and evaluation of deviations. The composition of artificial saliva was determined by measuring the mass fraction of the inorganic ions. The density of dried artificial saliva droplets was estimated using its composition and the density of each non-volatile component. The volume equivalent diameter (VED) of droplets have been measured by aerodynamic particle sizer (APS) and optical particle size spectrometer (OPSS). As a response to the COVID-19 pandemic, this is the first time that a comparative study among four metrology institutes has been conducted to evaluate the accuracy of saliva and saline droplet size measurement. For artificial saliva droplets measured by OPSS, the deviations from the reference VED (~4 μm) were below 5.3%. For saliva droplet sizes measured by APS, two institutes showed higher deviations up to 21.9% from the reference VED. For saline droplets measured by APS, the deviations from the reference VED were below 10.0%. The potential droplet size measurement errors using OPSS and APS have been discussed. This work underscores the need for new reference size standards to improve the accuracy and establish traceability in saliva and saline droplet size measurement.
... It is understood that whilst the airborne transmission potential of COVID-19 is not universally acknowledged (Ram et al., 2021), it is widely accepted that aerosol transmission routes can facilitate the inhalation of small droplets exhaled by an infected person (Buonanno, Stabile, & Morawska, 2020;Jayaweera, Perera, Gunawardana, & Manatunge, 2020;Lednicky et al., 2020;Li, Leung, & Tang, 2007;Miller et al., 2021;Morawska & Cao, 2020;Morawska & Milton, 2020;Wang & Du, 2020). Immediately after droplets are expired, the liquid content starts to evaporate, and some droplets become so small that transport by air current affects them more than gravitation (Morawska et al., 2009). These become droplet nuclei, which suspend in the air or are transported away by room airflow (Li et al., 2007) which can potentially infect susceptible members of the population. ...
... It is evident that an increase in the operating pressure correspondingly increased the particle number concentration, while the particle size distribution remained relatively unchanged. The generated aerosol droplets exhibited a size distribution similar 255 to that of most respiratory droplets, with a large fraction is smaller than 1 µm and a peak around 0.2 to 0.8 µm (Morawska et al., 2009;Zayas et al., 2012;Fabian et al., 2011). Furthermore, the particle number concentration of the DEHS droplets produced at a pressure of 2.0 bar aligns closely with the concentration of the cough-generated droplets (Zayas et al., 2012). ...
The application of ultraviolet (UV)-based air disinfection holds promise, but also presents several 10 challenges. Among these, the quantitative determination of the required UV radiation dose for aerosols is particularly significant. This study explores the possibility of determining the UV dose experienced by aerosols without the use of virus-containing aerosols, circumventing associated laboratory safety issues. To achieve this, we developed a model system comprised of UV-sensitive dyes dissolved in di-ethyl-hexyl-sebacate (DEHS), which facilitates the generation of non-evaporating and UV-degradable aerosols. For the selection of UV-sensitive 15 dyes, 20 dyes were tested, and two of them were selected as most suitable according to several selection criteria. Dye-laden aerosol droplets were generated using a commercial aerosol generator and subsequently exposed to UVC radiation in a laboratory-built UV irradiation chamber. We designed a low-pressure impactor to collect the aerosols pre-and post-UV exposure. Dye degradation, as a result of UV light exposure, was then analyzed by assessing the concentration changes in the collected dye solutions using a UV-visible spectrophotometer. Our 20 findings revealed that a UV dose of 245 mW·s·cm-2 resulted in a 10% degradation, while a lower dose of 21.6 mW·s·cm-2 produced a 5% degradation. In conclusion, our study demonstrates the feasibility of using aerosol droplets containing UV-sensitive dyes to determine the UV radiation dose experienced by an aerosol.
... Fine particulate matter, described by the total mass concentration of airborne particles smaller than 2.5 m in aerodynamic diameter (PM 2.5), can penetrate into human lungs and cause negative health outcomes including asthma and lung and heart diseases [1,2]. PM 2.5 is produced from both anthropogenic sources such as fuel combustion in automobiles and power plants [3], and natural sources such as respiratory droplets [4][5][6] and forest fires [7]. Various mitigation strategies have been developed and implemented based on the source of particulate matter. ...
A novel flowing plasma system aimed at increasing charging efficiency of particulate matter and effective removal through electrostatic precipitation is studied. Nanoparticles are passed through the spatial afterglow of an atmospheric pressure radio-frequency glow discharge plasma. Particle charging efficiencies and polarities are measured at different plasma-aerosol gaps, aerosol and plasma flow rates, plasma powers, and afterglow DC bias. Various timescales are calculated to explain the transport of charge carriers that facilitate particle charging processes. The experimental results showed increased charging efficiency and net positive charging at longer gaps between the afterglow and aerosol stream and lower aerosol flow rates. Timescale analysis indicates that when ample residence time is provided, transport of charge carriers shifts from ambi-polar diffusion to free diffusion, and electrons are rapidly lost from the afterglow, resulting in highly efficient, net positive charging of particles. The charging efficiency of particles in optimized operating conditions was comparable or higher than reported collection efficiencies of electrostatic precipitators. The findings overall demonstrate that glow discharges are capable of charging particles not immersed in the plasma bulk, and such systems show promise for improving performance of particle mitigation technology.
... All statistical analysis was performed using the MATLAB software package (The MathWorks Inc., Massachusetts). Building on existing models of aerosol production in the respiratory tract we use a log-normal distribution to model the distribution of total particle counts [16]. For the whole procedure data, a logarithm of the data is first computed, then a t-test is applied to compute p-values. ...
Study Aim: Upper GI endoscopies are considered aerosol generating procedures (AGP) that risk spread of airborne diseases such as SARS-CoV-2. We aim to investigate where clinically approved bronchoscopy masks applied to patients during EGDs can mitigate spread of aerosols and droplets. Materials and Methods: This study included patients undergoing routine upper GI endoscopy in a standard endoscopy room and used a particle counter to measure size and number of particles 10cm from the mouth of 55 patients undergoing upper GI endoscopies, of whom 12 wore bronchoscopy masks and 33 did not (control). Particle counts in the aerosol (≤5µm diameter) and droplet (>5µm diameter) size ranges were measured and averaged over the duration of procedures. Results: Use of bronchoscopy masks offers 47% (p=0.01) reduction in particle count for particles <5μm in diameter over the procedure duration (aerosols). Conclusions: Bronchoscopy masks or similar are a simple, low-cost mitigation technique that can be used during outbreaks of respiratory diseases such as COVID-19 to improve safety and reduce fallow times.
... The COVID-19 pandemic has emphasized the importance of air quality and its impact on viral prevalence in the environment and human health (Wardhani and Susan 2021) SARS-CoV-2 virus transmission through respiratory aerosols has been established, by now, as one of the main contagion routes during the pandemic (Watson et al., 2022) Space occupancy, duration of exposure, mask use, aerosol 18 generating actions (e.g., cough, sneeze, vocalization, laughter, breathing), ventilation (or lack thereof) and other factors can all affect the likelihood of indoor transmission by modulating the amount of infectious "doses" generated by infected individuals in a space, that can then infect other susceptible individuals (Morawska and Cao, 2020;Morawska et al., 2009) Public buy-in to comply with interventions focusing on these variables is a big hurdle in the third year of the pandemic, partly due to lower mortality rates and many severe cases attributed to vaccinations and the beforementioned indoor transmission-limiting interventions (Watson et al., 2022). Thus, studies that can help visualize the air quality in terms of the probability of COVID-19 transmission could greatly inform the population and help maintain low infection rates even during routine indoor activities. ...
We measured the indoor CO2 concentration in occupied areas with ventilation systems that recirculate air without an external air supply. The average time required to achieve the highest probability of contagion was also measured based on the number of participants in the group. Three different experimental groups were evaluated: Group One (G1), which included 5 participants; Group Two (G2), with 10 participants; and Group Three (G3), with 15 participants. Before the measurements, the CO2 concentration was measured to be homogeneous and its sampled value was given by the difference between the indoor and outdoor CO2 measurements (>5000 ppm or 0.5% CO2 in air) averaged over an 8-h work day Time-Weighted Average (TWA.). G1 and G3 group participants performed low-intensity daily office activities, such as reading and talking. In contrast, Group Two (G2) was asked to perform moderate intensity activities, such as frequently lifting 10 kg items and walking quickly. The CO2 concentration was measured with two instruments to compare the outdoor and indoor measurements. Both devices were configured to take one reading every second for 30 min. A mathematical model was developed from the CO2 concentrations measured, the group size, and the retention factor of the mask being worn to determine the probability of inhaled air contaminated with an aerosol of SARS-CoV-2. We concluded that the likelihood of contagion in enclosed areas such as study areas, offices, and meeting rooms, among others, which use ventilation without a circulation of fresh air, is high. Despite proper distancing and masking, there is a 99% chance of contagion in one of the modeled extreme case scenarios in less than 10 min of exposure. The study took place in Albrook, Republic of Panama, which is a tropical developing coastal geographic location where split air conditioning units are widely used and, like many other countries in Latin America, where indoor air quality has only recently started being discussed publicly and enforced.
... Most of the studies were based on retrospective analyses of real-world settings with many factors either left uncontrolled or not measured including; the viral load of the infectors, the number of infectors, the size of the susceptible population, infection risk of the host outside the investigated setting, and the influence of other NPIs etc. [29]. These factors can influence the risk of transmission; for example, the viral emission in aerosols emitted from infected subjects during different respiratory activities such as breathing, talking and singing have been reported to vary between 0 and 10 7 RNA copies per hour and the total volume of aerosols emitted is dependent on respiratory activity [30][31][32][33][34][35][36]. ...
The purpose of this review was to identify the effectiveness of environmental control (EC) non-pharmaceutical interventions (NPIs) in reducing transmission of SARS-CoV-2 through conducting a systematic review. EC NPIs considered in this review are room ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way-systems. Systematic searches of databases from Web of Science, Medline, EMBASE, preprint servers MedRxiv and BioRxiv were conducted in order to identify studies reported between 1 January 2020 and 1 December 2022. All articles reporting on the effectiveness of ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way systems in reducing transmission of SARS-CoV-2 were retrieved and screened. In total, 13 971 articles were identified for screening. The initial title and abstract screening identified 1328 articles for full text review. Overall, 19 references provided evidence for the effectiveness of NPIs: 12 reported on ventilation, 4 on air cleaning devices, 5 on surface disinfection, 6 on room occupancy and 1 on screens/barriers. No studies were found that considered the effectiveness of [Formula: see text] monitoring or the implementation of one-way systems. Many of these studies were assessed to have critical risk of bias in at least one domain, largely due to confounding factors that could have affected the measured outcomes. As a result, there is low confidence in the findings. Evidence suggests that EC NPIs of ventilation, air cleaning devices and reduction in room-occupancy may have a role in reducing transmission in certain settings. However, the evidence was usually of low or very low quality and certainty, and hence the level of confidence ascribed to this conclusion is low. Based on the evidence found, it was not possible to draw any specific conclusions regarding the effectiveness of surface disinfection and the use of barrier devices. From these results, we further conclude that community agreed standards for well-designed epidemiological studies with low risk of bias are needed. Implementation of such standards would enable more confident assessment in the future of the effectiveness of EC NPIs in reducing transmission of SARS-CoV-2 and other pathogens in real-world settings. This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the COVID-19 pandemic: the evidence'.
... There are three possible mechanisms for the generation of aerosol droplets [2]: the aerosol generation by bursts of bronchiole fluid film; the aerosols produced by shear-flow forces in large bronchi; and the droplets formed by the opening and closing of vocal folds in the larynx. The third type of aerosol is produced not only by coughing but also by speech production, and the amount of aerosol production in the speech was reported to be much larger than that in normal breathing [3][4]. Furthermore, it was found that the amount of aerosol varies depending on the type of phonemes [5]. ...
... 3 , 37˚Cand 92% respectively [30]. Meanwhile, the parameters of the patient's exhaled airflow were set according to literature [31]. For isolation ward inlet and outlet, the boundary condition for droplets in DPM was set as escape condition. ...
Due to the serious global harm caused by the outbreak of various viral infectious diseases, how to improve indoor air quality and contain the spread of infectious bioaerosols has become a popular research subject. Negative pressure isolation ward is a key place to prevent the spread of aerosol particles. However, there is still limited knowledge available regarding airflow patterns and bioaerosol diffusion behavior in the ward, which is not conducive to reducing the risk of cross-infection between health care workers (HCWs) and patients. In addition, ventilation layout and patient posture have important effects on aerosol distribution. In this study, the spatial and temporal characteristics as well as dispersion patterns of bioaerosols under different ventilation patterns in the ward were investigated using the computational fluid dynamics (CFD) technique. It is concluded that changes in the location of droplet release source due to different body positions of the patient have a significant effect on the bioaerosol distribution. After optimizing the layout arrangements of exhaust air, the aerosol concentration in the ward with the patient in both supine and sitting positions is significantly reduced with particle removal efficiencies exceeding 95%, that is, the ventilation performance is improved. Meanwhile, the proportion of aerosol deposition on all surfaces of the ward is decreased, especially the deposition on both the patient's body and the bed is less than 1%, implying that the risk of HCWs being infected through direct contact is reduced.
... The laryngeal aerosols are argued to be produced due to bursts of mucus liquid bridges between vocal folds. Studies that have compared particle concentrations in cough with those of sustained vocalization, such as the prolonged ''aah'', found that mucus liquid bridges produce particles not only during cough but also during voice production (Johnson et al., 2011;Morawska et al., 2009). ...
... Note that our measurements include droplets as small as 1 µm that originate from the unsteady rim retraction dynamics. Crucially, our measurements of the volume size distribution [ Fig. 7(b)] are inline with previously reported droplet statistics of bioaerosols exhaled during expiratory activities [64][65][66]. Previous investigations report the presence of both unimodal and bimodal log-normal size distributions in bioaerosols exhaled by humans. ...
We combine experiments and numerical computations to examine underlying fluid mechanical processes associated with bioaerosol generation during violent respiratory maneuvers, such as coughing or sneezing. Analogous experiments performed in a cough machine—consisting of a strong shearing airflow over a thin liquid film—allow us to illustrate the changes in film topology as it disintegrates into small droplets. We identify that aerosol generation during the shearing of the liquid film is mediated by the formation of inflated baglike structures. The breakup of these bags is triggered by the appearance of retracting holes that puncture the bag surface. Consequently, the cascade from inflated bags to droplets is primarily controlled by the dynamics and stability of liquid rims bounding these retracting holes. We also reveal the key role of fluid viscosity in the overall fragmentation process. It is shown that more viscous films when sheared produce smaller droplets.
... Furthermore, some individuals are "super speech emitters," having the ability to emit more aerosol particles than others. For example, a 10 minutes conversation with an infected, asymptomatic super emitter talking in an average volume, could generate an invisible "cloud" of approximately 6,000 aerosol particles that could potentially be inhaled by the other party [4][5][6]. Therefore, vital to study and understand the dynamics of the spread of cough and breathing particles of different sizes. ...
The 2019 novel coronavirus (SARS-CoV-2 / COVID-19), with a point of origin in Wuhan, China, has spread rapidly all over the world. It turned into a raging pandemic wrecking havoc on health care facilities, world economy and affecting everyone's life to date. With every new variant, rate of transmission, spread of infections and the number of cases continues to rise at an international level and scale. There are limited reliable researches that study microdroplets spread and transmissions from human sneeze or cough in the airborne space. In this paper, we propose an intelligent technique to visualize, detect, measure the distance of spread in a real-world settings of microdroplet transmissions in airborne space, called "COVNET45". In this paper, we investigate the microdroplet transmission and validate the measurements accuracy compared to published researches, by examining several microscopic and visual images taken to investigate the novel coronavirus (SARS-CoV-2 / COVID-19). The ultimate contribution is to calculate the spread of the microdroplets, measure it precisely and provide a graphical presentation. Additionally, the work employs machine learning and five algorithms for image optimization, detection and measurement.
... Additionally, the particle population will change in space and time due to the rapid evaporation of the droplet water content, further exacerbating the task. These complications greatly limit the effectiveness of historical diagnostic tools, such as the Aerodynamic Particle Sizer (APS), [18][19][20] which sizes particles from 0.5 to 20 μm in diameter and returns time-averaged sizing information from a singular area in space. This tool collects a sample using a mechanical probe, whereby aerosols are guided into the analyser. ...
SARS‐CoV‐2 and its ever‐emerging variants are spread from host‐to‐host via expelled respiratory aerosols and saliva droplets. Knowing the number of virions which are exhaled by a person requires precise measurements of the size, count, velocity and trajectory of the virus‐laden particles that are ejected directly from the mouth. These measurements are achieved in 3D, at 15,000 images/s, and are applied when speaking, yelling and coughing. In this study, 33 events have been analysed by post‐processing ∼500,000 images. Using these data, the flow rates of SARS‐CoV‐2 virions have been evaluated. At high concentrations, 10 ⁷ virions/mL, it is found that 136–231 virions are ejected during a single cough, where the virion flow rate peak is capable of reaching 32 virions within a millisecond. This peak can reach tens of virions/ms when yelling but reduced to only a few virions/ms when speaking. At medium concentrations, ∼10 ⁵ virions/mL, those results are hundreds of times lower. The total number of virions that are ejected when yelling at 110 dB, instead of speaking at 85 dB, increases by two‐ to threefold. From the measured data analysed in this article, the flow rate of other diseases, such as influenza, tuberculosis or measles, can also be estimated. As these data are openly accessible, they can be used by modellers for the simulation of saliva droplet transport and evaporation, allowing to further advance our understanding of airborne pathogen transmission.
Key points
Advanced, optimized and combined laser‐based imaging techniques for temporally sizing and tracking respiratory droplets and aerosols.
Understanding how pathogens are being ejected from the mouth when speaking, yelling and coughing.
Quantifying and analysing the variation of SARS‐CoV‐2 flow rates emission during exhalation.
... Background COVID-19 disease, caused by the novel SARS-CoV-2 virus, can be transmitted from human to human by multiple means, including respiratory droplets, aerosols, and fomites [1,2]. According to numerous studies, the principal mode of transmission of SARS-CoV-2 is exposure to airborne respiratory particles (respiratory droplets and aerosols) carrying the virus [3][4][5][6]. Here, we define droplets as liquid airborne particles with diameters >100 µm, while aerosols are made up of particles 100 µm and smaller, consistent with Wang et al. [6]. ...
Background
The COVID-19 pandemic was caused by the SARS-CoV-2 coronaviruses transmitted mainly through exposure to airborne respiratory droplets and aerosols carrying the virus.
Objective
To assess the transport and dispersion of respiratory aerosols containing the SARS-CoV-2 virus and other viruses in a small office space using a diffusion-based computational modeling approach.
Methods
A 3-D computational model was used to simulate the airflow inside the 70.2 m³ ventilated office. A novel diffusion model accounting for turbulence dispersion and gravitational sedimentation was utilized to predict droplet concentration transport and deposition. The numerical model was validated and used to investigate the influences of partition height and different ventilation rates on the concentration of respiratory aerosols of various sizes (1, 10, 20, and 50 µm) emitted by continuous speaking.
Results
An increase in the hourly air change rate (ACH) from 2.0 to 5.6 decreased the 1 μm droplet concentration inside the office by a factor of 2.8 and in the breathing zone of the receptor occupant by a factor of 3.2. The concentration at the receptor breathing zone is estimated by the area-weighted average of a 1 m diameter circular disk, with its centroid at the center of the receptor mannequin mouth. While all aerosols were dispersed by airflow turbulence, the gravitational sedimentation significantly influenced the transport of larger aerosols in the room. The 1 and 10 μm aerosols remained suspended in the air and dispersed throughout the room. In contrast, the larger 20 and 50 μm aerosols deposited on the floor quickly due to the gravitational sedimentation. Increasing the partition between cubicles by 0.254 m (10”) has little effect on the smaller aerosols and overall exposure.
Impact
This paper provides an efficient computational model for analyzing the concentration of different respiratory droplets and aerosols in an indoor environment. Thus, the approach could be used for assessing the influence of the spatial concentration variations on exposure for which the fully mixed model cannot be used.
... To achieve this objective, a low background environment was required; therefore, we conducted our experiments in an ISO standard class 5 clean room. The measurement of droplets due to expiratory activities was performed by Morawska [2] using a small wind tunnel in which the subject could put their head and in which a built-in HEPA filter provided a clean environment. In this study, a zinc-based duct with a ventilation fan was installed in a clean room to enable simple measurements. ...
Due to the COVID-19 pandemic, research on the quantitative evaluation of the risk of infection has become necessary. Because airborne transmission occurs by the inhalation of droplets from infected people, understanding the mechanism of droplet generation is important. In this study, the size distribution of droplets produced by various expiratory activities was investigated, the results were compared with those of previous studies, and the applicability of the simple measurement method was confirmed. The experiment was performed using an optical particle counter and a device that could continuously ventilate the generated droplets in a clean room with a low background concentration. Among the variables in the equation for calculating the quanta emission rate to evaluate the risk of infection, the droplet concentration and inhalation rates that could be measured were determined, and the relative risk of infection for each of the various expiratory activities was quantitatively evaluated. In addition to the cases identical to those in previous studies, conversations and vocalizations were conducted while wearing a mask. Particles smaller than 1 μm were analyzed based on the theory that viruses have a high proliferation rate and a high risk of infection. The concentration of droplets produced by the expiratory activity was dominated by particles with a number concentration of <1 μm; however, the mass concentration was only observed at a low rate. The risk of infection increased in proportion to the volume of voice, and was markedly higher in the case of loud voices. In addition, the risk of infection decreased when wearing a mask, and the extent of reduction varied depending on the method of wearing the mask.
... Given these circumstances, there is a pressing need to explore methods for examining the sedimentation of droplets or aerosols, particularly in the context of the ongoing pandemic. Since the outbreak of SARS in 2003, numerous studies have examined the physicochemical properties of droplets in both outdoor and indoor environments [10,11,12,13]. Large size droplets (with a diameter of 50 μm or more) tend to settle rapidly on the ground due to the dominant gravity. ...
Contaminated surfaces play a significant role in the transmission of respiratory infectious diseases. To address this issue, we presented a novel quantitative detection method for droplets on physical surfaces, based on Laser-Induced Fluorescence (LIF) technique. The proposed detection method was demonstrated in a realistic high-speed train compartment scenario by simulating the process of droplet release during passengers' breathing and coughing. The experimental results showed that this method could offer high precision (10−1 mg/m2) for detecting minute substance concentrations, and its ease of operation makes it suitable for complex engineering environments. The results also revealed that under the combined effects of the indoor airflow and breathing airflow, the range of droplets released by breathing activity exceeded two rows in front and behind the release position. Simultaneously, we observed that a large number of droplets settled on the seat surfaces on both sides of the same row as the releaser, with over 36% of these droplets concentrated on the backrest area of the seats. As the respiratory jet velocity increased, the location with the most sediment droplets (accounting for 8% of the total sedimentation) occurred on the seat directly in front of the releaser, and approximately 48% of the droplets were found on the back of this seat. Our proposed method overcomes the shortcomings of existing experimental methods in quantitatively capturing the motion characteristics of droplets in complex flow fields.
... Large droplets would deposit on the inanimate surfaces due to gravity, causing indirect person-to-person transmission through fomites. Some droplets would evaporate to form droplet nuclei of smaller size of 0.8-3 µm [22], which can suspend and remain in the air for a long period of time and move along the airflow over a long distance [23,24]. Notably, some may concern about the physical dissimilarities of expiratory droplets and tracer gas molecules and question the appropriateness of using tracer gas to mimic the movement of infectious aerosols. ...
... Since the range of changes in the diameter of droplets during breathing is small, in some studies, a mean diameter was considered for the all outlet droplets (Zhang et al., 2019). Issa (Issa, 2021) reviewed previous studies on the size distribution of respiratory droplets during breathing (Morawska et al., 2009;Fabian et al., 2008;Johnson et al., 2011), and as shown in Fig. 4, a mean diameter of the outlet droplets is around 1 μm (average diameter = 0.64 μm). ...
... People can release droplets and aerosols by coughing, sneezing, and some normal exhalation behaviors such as breathing, speaking, and singing (Alsved et al., 2020;Morawska and Milton, 2020;Stadnytskyi et al., 2020). After quickly evaporating into droplet nuclei, SARS-CoV-2 aerosols can float and be transported over long distances (Morawska et al., 2009), remain viable and infectious for several hours (van Doremalen et al., 2020), accumulate in enclosed spaces, and be inhaled deep into the lungs leading to more severe infection (Chu et al., 2020;Milton, 2020). The emergence of new SARS-CoV-2 variants, Delta (Planas et al., 2021) and Omicron (Karim and Karim, 2021), which have higher airborne transmissibility, have prompted the urgent need for monitoring of SARS-CoV-2 aerosols. ...
Airborne transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has highlighted the urgent need for aerosol monitoring of SARS-CoV-2 to prevent sporadic outbreaks of COVID-19. The inadequate sensitivity of conventional methods and the lack of an on-site detection system limited the practical SARS-CoV-2 monitoring of aerosols in public spaces. We have developed a novel SARS-CoV-2-in-aerosol monitoring system (SIAMs) which consists of multiple portable cyclone samplers for collecting aerosols from several venues and a sensitive "sample-to-answer" microsystem employing an integrated cartridge for the analysis of SARS-CoV-2 in aerosols (iCASA) near the sampling site. By seamlessly combining viral RNA extraction based on a chitosan-modified quartz filter and "in situ" tetra-primer recombinase polymerase amplification (tpRPA) into an integrated microfluidic cartridge, iCASA can provide an ultra-high sensitivity of 20 copies/mL, which is nearly one order of magnitude greater than that of the commercial kit, and a short turnaround time of 25 min. By testing various clinical samples of nasopharyngeal swabs, saliva, and exhaled breath condensates obtained from 23 COVID-19 patients, we demonstrate that the positive rate of our system was 3.3 times higher than those of the conventional method. Combining with multiple portable cyclone samplers, we detected 52.2% (12/23) of the aerosol samples, six times higher than that of the commercial kit, collected from the isolation wards of COVID-19 patients, demonstrating the excellent performance of our system for SARS-CoV-2-in-aerosol monitoring. We envision the broad application of our microsystem in aerosol monitoring for fighting the COVID-19 pandemic.
The reopening of an occluded airway can lead to the formation of droplets and aerosols, which can be released during exhalation, providing a possible mechanism of disease transmission. In this study, the flow behavior of airway occlusions (“plugs”) close to their point of rupture is examined using a free-surface model (volume of fluid), such that factors influencing the formation of droplets during their reopening can be identified. The propagation of airway occlusions is highly influenced by recirculating flow at the edge of the front interface, where significant fluctuations of wall shear stresses occur. The resulting drag force causes the rear interface to advance at a greater rate, destabilizing the plug. As the plug thickness decreases, a thin film with uniform thickness forms, resulting in a disk-like structure around the centerline. Rupture occurs around the disk formation largely due to surface tension instability. At lower pressures, smaller disks form causing the rupture to occur through a puncture point (forming no droplets); at higher pressures, a larger disk forms, with rupture occurring along the disk edge and at the center (forming multiple droplets). Upon reopening, a jet of air is produced, causing a temporary increase in shear stress along the wall. However, the magnitude and duration of this increase do not scale directly to the applied pressure, as the formation of droplets and irregularities in airway lining were found to disrupt the flow field and the shear stresses at the wall.
The global COVID-19 outbreak in 2020 has made understanding pathogen-laden aerosol transport and the associated transmission routes more relevant than ever. To determine how aerosol particles generated by continuous breathing accumulate in confined spaces, the particle concentrations in a small room resembling a train entrance are investigated. The room is ventilated and equipped with two heated manikins, one of which is continuously exhaling aerosol through the mouth for 30 min. For this setup we conducted local particle measurements in the center plane and a RANS simulation including the prediction of the transient particle transport. It is shown that the particle concentration increases logarithmically and attains a nearly steady state. The resulting local particle concentrations normalized to the source concentrations are subsequently compared. We find good agreement with the experiment in the exhalation zone of the breathing manikin and larger differences for the sensor positions beneath the ventilation inlet.
The COVID-19 pandemic has spotlit the scientific field of fluid dynamics governing airborne transmission through virus-laden mucosal-salivary droplets. In this work, a mathematical model for airborne droplet dispersion and viral transmission centered on evaporating droplets containing solid residue was proposed. Droplet dynamics are influenced by factors such as initial velocity, relative humidity (RH), and solid residue, in agreement with analytical and experimental results. Interestingly, the maximum droplet dispersion distance depends strongly on initial droplet size and RH, such as 0.8-mm-diameter droplet at 0.3 RH, 1.0 mm at 0.6 RH, and 1.75 mm at 0.9 RH, but only weakly on initial projected velocity. Under realistic conditions, an evaporating sputum droplet can cover a dispersion distance at least three times than that of a pure water droplet. Based on Wells falling curves, the critical droplet size, the largest droplet that can remain suspended in air without settling due to gravity, ranges from 120 μm at 0.3 RH to 75 μm at 0.9 RH. Together, our results highlight the role of evaporation on droplet lifetime, dispersion distance, and transmission risks.
The evidence of airborne transmission of Covid-19 through respiratory aerosols, and the experienced restrictions on commercial activity reinforce the necessity of a paradigm shift in the design of building ventilation systems for this new post-pandemic context. Therefore, this study has used a coupled multizone-CFD code developed by the National Institute of Standards and Technology (NIST) and an infection risk model on ventilation analysis for a small office application. The influence of different ventilation modes and air filtration efficiencies on infection risk was assessed. The code was validated by a high-quality benchmark, and the results demonstrate that the simulations reproduce the basic performance of the ventilation strategies that were selected. The purposes of this study are to assess the reduction of airborne infection risk of Covid-19 due to ventilation strategies and to present a framework that may contribute to the selection of rational solutions for the future challenges in this new post-pandemic era.KeywordsCovid-19Infection controlCFDVentilationAirborne
Upper-room ultraviolet germicidal irradiation (UVGI) technology can potentially inhibit the transmission of airborne disease pathogens. There is a lack of quantitative evaluation of the performance of the upper-room UVGI for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) airborne transmission under the combined effects of ventilation and UV irradiation. Therefore, this study aimed to explore the performance of the upper-room UVGI system for reducing SARS-CoV-2 virus transmission in a hospital isolation environment. Computational fluid dynamics and virological data on SARS-CoV-2 were integrated to obtain virus aerosol exposure in the hospital isolation environment containing buffer rooms, wards and bathrooms. The UV inactivation model was applied to investigate the effects of ventilation rate, irradiation flux and irradiation height on the upper-room UVGI performance. The results showed that increasing ventilation rate from 8 to 16 air changes per hour (ACH) without UVGI obtained 54.32% and 45.63% virus reduction in the wards and bathrooms, respectively. However, the upper-room UVGI could achieve 90.43% and 99.09% virus disinfection, respectively, with the ventilation rate of 8 ACH and the irradiation flux of 10 μW cm-2. Higher percentage of virus could be inactivated by the upper-room UVGI at a lower ventilation rate; the rate of improvement of UVGI elimination effect slowed down with the increase of irradiation flux. Increase irradiation height at lower ventilation rate was more effective in improving the UVGI performance than the increase in irradiation flux at smaller irradiation height. These results could provide theoretical support for the practical application of UVGI in hospital isolation environments.
The importance of building ventilation in avoiding long-distance airborne transmission has been highlighted with the advent of the COVID-19 pandemics. Among others, school environments, in particular classrooms, present criticalities in the implementation of ventilation strategies and their impact on indoor air quality and risk of contagion. In this work, three naturally ventilated school buildings located in northern Italy have undergone monitoring at the end of the heating season. Environmental parameters, such as CO2 concentration and indoor/outdoor air temperature, have been recorded together with the window opening configurations to develop a two-fold analysis: i) the estimation of real air change rates through the transient mass balance equation method, and ii) the individual infection risk via the Wells-Riley equation. A strong statistical correlation has been found between the air change rates and the windows opening configuration by means of a window-to-volume ratio between the total opening area and the volume of the classroom, which has been used to estimate the individual infection risk. Results show that the European Standard recommendation for air renewal could be achieved by a window opening area of at least 1.5 m2, in the most prevailing Italian classrooms. Furthermore, scenarios in which the infector agent is a teacher show higher individual infection risk than those in which the infector is a student. In addition, the outcomes serve school staff as a reference to ensure adequate ventilation in classrooms and keep the risk of infection under control based on the number of the students and the volume of the classroom.
Water contains enormous amounts of energy yet to be fully utilized. Although humans have been able to extract energy from liquid water, gaseous moisture is often regarded as an underutilized...
In the fifth wave of the COVID-19 epidemic in Hong Kong in early 2022, the large number of infected persons caused a shortage of ambulances and transportation vehicles operated by the government. To solve the problem, taxi drivers were recruited to transport infected persons to hospitals in their taxis. However, many of the drivers were infected after they began to participate in the plan. To tackle this issue, the present study numerically evaluated the effectiveness of several intervention measures in reducing the infection risk for taxi drivers. First, experiments were conducted inside a car to validate the large-eddy simulation (LES)-Lagrangian model for simulation of particle transport in a car. The validated model was then applied to calculate the particle dispersion and deposition in a Hong Kong taxi with intervention measures that included opening windows, installing partitions, and using a far-UVC lamp. The results show that opening the windows can significantly reduce the driver's total exposure by 97.4 %. Installing partitions and using a far-UVC lamp can further reduce the infection risk of driver by 55.9 % and 32.1 %, respectively. The results of this study can be used to support the implementation of effective intervention measures to protect taxi drivers from infection.
To understand the generation process of airborne droplets during exhalation, this study investigates the mechanism of bimodal characteristics of the size distribution of droplets generated in a condensed spray flow. The phase change process in the condensed spray flow was estimated based on the droplet size distribution measured by a phase Doppler particle analyzer and the temperature distribution measured by a thermistor. On the central axis, the size distribution was unimodal in the spray interior. In contrast, bimodality of the size distribution at the outer edge of the spray flow was observed. At the edge of the spray flow, a large temperature gradient was formed. This indicates that condensation actively occurred at the outer edge. For the same reason as outlined above, condensation did not progress at the spray center because of the consumption of water vapor at the outer edge by the condensation, and the droplet diameter did not change significantly. Hence, owing to the difference in the local phase change process between the center and outer edge of the spray, large and small droplets can exist simultaneously in the middle region. As a result, the size distribution of the condensation spray is bimodal.
Disposable surgical masks emerged as a solution to the increasing protection demands against fine/ultrafine particulate matter. It was prompted by the SARS-CoV-2 pandemic and the escalating levels of air pollution...
Respiratory viruses are a major public health burden across all age groups around the globe, and are associated with high morbidity and mortality rates. They can be transmitted by multiple routes, including physical contact or droplets and aerosols, resulting in efficient spreading within the human population. Investigations of the cell biology of virus replication are thus of utmost importance to gain a better understanding of virus-induced pathogenicity and the development of antiviral countermeasures. Light and fluorescence microscopy techniques have revolutionized investigations of the cell biology of virus infection by allowing the study of the localization and dynamics of viral or cellular components directly in infected cells. Advanced microscopy including high- and super-resolution microscopy techniques available today can visualize biological processes at the single-virus and even single-molecule level, thus opening a unique view on virus infection. We will highlight how fluorescence microscopy has supported investigations on virus cell biology by focusing on three major respiratory viruses: respiratory syncytial virus (RSV), Influenza A virus (IAV) and SARS-CoV-2. We will review our current knowledge of virus replication and highlight how fluorescence microscopy has helped to improve our state of understanding. We will start by introducing major imaging and labeling modalities and conclude the chapter with a perspective discussion on remaining challenges and potential opportunities.
The potential for masks to act as fomites in the transmission of SARS-CoV-2 has been suggested but not demonstrated experimentally or observationally. In this study, we aerosolized a suspension of SARS-CoV-2 in saliva and used a vacuum pump to pull the aerosol through six different types of masks. After 1 h at 28 °C and 80% RH, SARS-CoV-2 infectivity was not detectable on an N95 and surgical mask, was reduced by 0.7 log10 on a nylon/spandex mask, and was unchanged on a polyester mask and two different cotton masks when recovered by elution in a buffer. SARS-CoV-2 RNA remained stable for 1 h on all masks. We pressed artificial skin against the contaminated masks and detected the transfer of viral RNA but no infectious virus to the skin. The potential for masks contaminated with SARS-CoV-2 in aerosols to act as fomites appears to be less than indicated by studies involving SARS-CoV-2 in very large droplets.
Introduction:
In health care, measures against cross-transmission of microorganisms are codified by standard precautions, and if necessary, they are supplemented by additional precautions.
State of the art:
Several factors impact transmission of microorganisms via the respiratory route: size and quantity of the emitted particles, environmental conditions, nature and pathogenicity of the microorganisms, and degree of host receptivity. While some microorganisms necessitate additional airborne or droplet precautions, others do not.
Prospects:
For most microorganisms, transmission patterns are well-understood and transmission-based precautions are well-established. For others, measures to prevent cross-transmission in healthcare facilities remain under discussion.
Conclusions:
Standard precautions are essential to the prevention of microorganism transmission. Understanding of the modalities of microorganism transmission is essential to implementation of additional transmission-based precautions, particularly in view of opting for appropriate respiratory protection.
In this study, the effects of sneeze velocity profiles, including peak velocity (PV), peak velocity time (PVT), and sneeze duration time (SDT), on the dispersion of respiratory droplets were studied experimentally and numerically. Spatial–temporal datasets of droplet velocity exhaled from several subjects' mouths with different physiological characteristics were obtained by particle image velocimetry. A direct relationship was found between the forced vital capacity and PV, while the subject's body mass index significantly affected the SDT. A transient computational fluid dynamics (CFD) approach using the renormalization group k–ε turbulence model in conjunction with the Lagrangian particle tracking was developed and used to simulate sneeze droplet motion characteristics. Both one-way and two-way (humidity) coupling models were used in these simulations. The CFD results showed that the two-way (humidity) coupling model provided better agreement with the data in the turbulent and expanded puff zones than the one-way coupling model. The one-way model led to reasonably accurate results in the fully dispersed and dilute-dispersed droplet phases. The effect of injection duration time and injection angle on PVT was larger than that on PV values, while the effect of initial injection velocity on PV was higher than that on PVT values. In addition, the initial injection velocity and angle significantly affected the maximum spreading distance of droplets dmax,sp. The numerical results obtained from the dilute-dispersed droplet phase were in good agreement with the trajectories of isolated droplets in the experimental data. The findings of this study provide novel insights into the effect of sneeze velocity profiles on dmax,sp, and the sneezer subject physiological effect on the threshold distance for the transmission of respiratory pathogens in a confined space.
The aim of this study is to evaluate the infection risk of aircraft passengers seated within and beyond two rows of the index case(s) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A(H1N1)pdm09 virus, and SARS-CoV-1. PubMed databases were searched for articles containing information on air travel–related transmission of SARS-CoV-2, influenza A(H1N1)pdm09 virus, and SARS-CoV-1 infections. We performed a meta-analysis of inflight infection data. In the eight flights where the attack rate could be calculated, the inflight SARS-CoV-2 attack rates ranged from 2.6% to 16.1%. The risk ratios of infection for passengers seated within and outside the two rows of the index cases were 5.64 (95% confidence interval (CI):1.94–16.40) in SARS-CoV-2 outbreaks, 4.26 (95% CI:1.08–16.81) in the influenza A(H1N1)pdm09 virus outbreaks, and 1.91 (95% CI:0.80–4.55) in SARS-CoV-1 outbreaks. Furthermore, we found no significant difference between the attack rates of SARS-CoV-2 in flights where the passengers were wearing masks and those where they were not ( p = 0.22). The spatial distribution of inflight SARS-CoV-2 outbreaks was more similar to that of the influenza A(H1N1)pdm09 virus outbreaks than to that of SARS-CoV-1. Given the high proportion of asymptomatic or pre-symptomatic infection in SARS-CoV-2 transmission, we hypothesised that the proximity transmission, especially short-range airborne route, might play an important role in the inflight SARS-CoV-2 transmission.
The outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused an unparalleled disruption to daily life. Given that COVID-19 primarily spreads in densely populated indoor areas, urban public transport (UPT) systems pose significant risks. This study presents an analysis of the air change rate in buses, subways, and high speed trains based on measured CO2 concentrations and passenger behaviors. The resulting values were used as inputs for an infection risk assessment model, which was used to quantitatively evaluate the effects of various factors, including ventilation rates, respiratory activities, and viral variants, on the infection risk. The findings demonstrate that ventilation has a negligible impact on reducing average risks (less than 10.0%) for short-range scales, but can result in a reduction of average risks by 32.1%-57.4% for room scales. When all passengers wear masks, the average risk reduction ranges from 4.5-folds to 7.5-folds. Based on our analysis, the average total reproduction numbers (R) of subways are 1.4-folds higher than buses, and 2-folds higher than high speed trains. Additionally, it is important to note that the Omicron variant may result in a much higher R value, estimated to be approximately 4.9-folds higher than the Delta variant. To reduce disease transmission, it is important to keep the R value below 1. Thus, two indices have been proposed: time-scale based exposure thresholds and spatial-scale based upper limit warnings. Mask wearing provides the greatest protection against infection in the face of long exposure duration to the omicron epidemic.
Characterizing the size distribution of airborne particles carrying SARS-CoV-2 virus is essential for understanding and predicting airborne transmission and spreading of COVID-19 disease in hospitals as well as public and home indoor settings. Nonetheless, few data are currently available on virus-laden particle size distribution. Thus, the aim of this study is reporting the total concentrations and size distributions of SARS-CoV-2- genetic material in airborne particles sampled in hospital and home environments. A nanoMOUDI R122 cascade impactor (TSI, USA) was used to collect size-segregated aerosol down to the sub-micron range in home and in three different hospital environments in presence of infected patients in order to provide the concentration of airborne SARS-CoV-2 genetic material for each particle size range at different sampling locations. Providing one of the largest datasets of detailed size-fractionated airborne SARS-CoV-2 RNA to date, we found that 45.2 % of the total sub- and super-micrometric fractions were positive for SARS-CoV-2 with its genetic material being present in 17.7 % of sub-micrometric (0.18-1 μm) and 81.9 % of super-micrometric (>1 μm) fractions. The highest concentration of SARS-CoV-2 genetic material in total suspended particles (5.6 ± 3.4 RNA copies m-3) was detected in the room occupied with patients with more severe COVID-19 symptoms collected during the patients' high flow nasal oxygen therapy. The highest concentration at certain particle size fraction strongly depends on the sampling environment. However, the contribution of SARS-CoV-2 genetic material was in favour of super-micrometric compared to sub-micrometric particle size range. The evaluation of the individual risk of infection was carried out on the basis of the obtained data considering a hypothetical exposure scenario. The obtained results indicate the necessity of the protective masks in presence of infected subjects, especially while staying for longer period of time in the hospital environments.
Humans commonly exhale aerosols comprised of small droplets of airway-lining fluid during normal breathing. These “exhaled bioaerosols” may carry airborne pathogens and thereby magnify the spread of certain infectious diseases, such as influenza, tuberculosis, and severe acute respiratory syndrome. We hypothesize that, by altering lung airway surface properties through an inhaled nontoxic aerosol, we might substantially diminish the number of exhaled bioaerosol droplets and thereby provide a simple means to potentially mitigate the spread of airborne infectious disease independently of the identity of the airborne pathogen or the nature of any specific therapy. We find that some normal human subjects expire many more bioaerosol particles than other individuals during quiet breathing and therefore bear the burden of production of exhaled bioaerosols. Administering nebulized isotonic saline to these “high-producer” individuals diminishes the number of exhaled bioaerosol particles expired by 72.10 ± 8.19% for up to 6 h. In vitro and in vivo experiments with saline and surfactants suggest that the mechanism of action of the nebulized saline relates to modification of the physical properties of the airway-lining fluid, notably surface tension.
• drug delivery
• lung
• infectious disease
• influenza
This work investigated the size distribution of the droplet nuclei and coughed droplets by test subjects. The size distributions of droplet nuclei coughed by test subjects were determined with an aerodynamic particle sizer (APS) and scanning mobility particle sizer (SMPS) system (system 1). Coughed droplets were only sampled with the APS system (system 2). Two different schemes were employed in system 2. Furthermore, the size distribution of coughed droplets of different ages and gender was investigated to identify the effects of age and gender on droplet size distribution. Results indicated the total average size distribution of the droplet nuclei was 0.58-5.42 microm, and 82% of droplet nuclei centered in 0.74-2.12 microm. The entire average size distribution of the coughed droplets was 0.62-15.9 microm, and the average mode size was 8.35 microm. The size distribution of the coughed droplets was multimodal. The size distribution of coughed droplets showed three peaks at approximately 1 microm, 2 microm, and 8 microm. These analytical findings indicate that variation for average droplet size among the three age groups was insignificant (p > 0.1). Moreover, the variation in average droplet size between males and females was also insignificant (p > 0.1). Also, the variation in droplet concentration between males and females was significant (p > 0.1). Droplet nuclei concentrations from male subjects were considerably higher than that from females. Comparison of the droplet concentrations for subjects in different age groups demonstrated that subjects in the 30-50-year age group have the largest droplet concentrations.
The study of aerosols in indoor air and the assessment of human exposure to aerosols are relatively recent activities. The terms indoor air and exposure assessment refer primarily to nonindustrial settings, such as homes, offices, and public-access buildings (e.g., museums, airport terminals, retail stores). Although many occupational settings are 'indoors', the aerosol concentrations and constituents, airflow regimes, and turbulence levels pose related, but different, aerosol measurement constraints. Until recently, it was commonly believed that the quality of indoor air was superior to that of the outdoor (ambient) air nearby. Several factors have influenced the apparent deterioration of indoor air quality: life-styles have changed; building construction techniques have changed; and people have become more concerned about environmental tobacco smoke (ETS).
The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and 20 m in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8–10 m), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8-m drops to 25% for 10-m drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument's inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations.
In order to estimate the growth and deposition of hygroscopic aerosol particles during respiration the relative humidity (RH) of the air in the airways must be known. The RH has been calculated with a transport theory for the heat and water vapour in a tube using a numerical method, Cartesian coordinates, and nasal respiration [Ferron et al., J. Aerosol Sci. (1983) 14, 196; Ferron et al., Bull. math. Biol. (1985) 47, 565]. A similar theory is described here to calculate the transport for cylindrical coordinates, both for nasal and oral respiration. The method has the advantage of a reduced computational time compared with the method used before.Calculations are carried out both for nasal and oral inhalation and exhalation. The values of several parameters of the theory, the thickness of the boundary layer, the additional diffusivity by airflow instabilities, the profiles for the temperature and RH at the airway wall, are chosen to fit experimental data on the mean air temperature and RH in the human airways. Since the experimental data are scattered, maximum and minimum curves for the experimental data are derived. It was found mathematically that the RH of the air is more strongly dependent on the RH at the airway wall and less on its temperature. However due to the large uncertainties of the experimental data on the RH no firm conclusion can be drawn.
The aerodynamic particle sizer (APS, Model 3320, TSI Inc., St. Paul, MN) is an instrument that counts and sizes particles by time-of-flight, an aerodynamic property, and/or by light-scattering intensity, an optical property. If the counting efficiency of the APS 3320, defined as the number of particles counted divided by the number sampled is not 1.0 for particles of all sizes, then the reported size distributions and particle concentrations will be biased.A laboratory aerosol was sampled with two APS 3320s alternating between collecting only time-of-flight data in summing mode and collecting simultaneous time-of-flight and light-scattering intensity data in correlated mode. Collecting data in correlated mode resulted in errors in the reported aerodynamic size distributions and concentrations. The magnitude of the concentration error was an inverse function of concentration, ranging from approximately 10% at to 45% at .Experiments were also conducted to determine the counting efficiency of the APS 3320 in summing mode by comparing size distributions obtained with the analyzer to those obtained with a cascade impactor. Counting efficiency increased from 30% for particles to 100% for particles, then decreased to 60% for particles. For particles larger than about , the size distribution reported by the APS 3320 was distorted by artificial particle counts. To determine accurate particle size distributions and concentrations, the values reported by this instrument must be adjusted for counting efficiency.
Measurements were made of the number concentrations of particles in exhaled breath under various conditions of exercise. A laser light scattering particle spectrometer was used to count particles exhaled by test subjects wearing respirators in a challenge environment of clean, dry air. Precautions were taken to ensure that particles were not generated by the the respirators and that no extraneous water or other particles were produced in the humid exhaled air. The number of particles detected in exhaled air varied over a range from less than 0.1 to about 4 particles per cm3 depending upon the test subject and his activity. Subjects at rest exhaled the lowest concentration of particles, whereas exercises producing a faster respiration rate caused increased exhalation of particles. Exhaled particle concentrations can limit the usefulness of nondiscriminating, ambient challenge aerosols for the fit testing of highly protective respirators.
Droplets carried in exhaled breath may carry microorganisms capable of transmitting disease over both short and long distances. The size distribution of such droplets will influence the type of organisms that may be carried as well as strategies for controlling airborne infection. The aim of this study was to characterize the size distribution of droplets exhaled by healthy individuals. Exhaled droplets from human subjects performing four respiratory actions (mouth breathing, nose breathing, coughing, talking) were measured by both an optical particle counter (OPC) and an analytical transmission electron microscope (AEM). The OPC indicated a preponderance of particles less than 1 mu, although larger particles were also found. Measurements with the AEM confirmed the existence of larger sized droplets in the exhaled breath. In general, coughing produced the largest droplet concentrations and nose breathing the least, although considerable intersubject variability was observed.
Adequate air conditioning in the nasal airways is mandatory for respiration and gas exchange in the lower respiratory tract. The aim of the present study was to measure relative humidity and temperature in the airstream at different sites within the nasal cavity for mapping of relative humidity and temperature in the upper airways.
Intranasal relative humidity and temperature of 23 volunteers was measured during respiration at different locations in the nasal cavity.
The end-inspiratory temperature and humidity data, obtained with a miniaturized thermocouple and a capacitive humidity sensor, were determined.
A high increase of humidity and temperature at the end of inspiration, in relation to the environmental conditions, was found in the anterior nasal segment. The further increase of both parameters between turbinate area and nasopharynx was less pronounced in spite of the longer distance.
The anterior part of the nasal cavity contributes within a short nasal passage to air conditioning of inspired air.
Certain respiratory tract infections are transmitted through air. Coughing and sneezing by an infected person can emit pathogen-containing particles with diameters less than 10 microm that can reach the alveolar region. Based on our analysis of the sparse literature on respiratory aerosols, we estimated that emitted particles quickly decrease in diameter due to water loss to one-half the initial values, and that in one cough the volume in particles with initial diameters less than 20 microm is 60 x 10(-8) mL. The pathogen emission rate from a source case depends on the frequency of expiratory events, the respirable particle volume, and the pathogen concentration in respiratory fluid. Viable airborne pathogens are removed by exhaust ventilation, particle settling, die-off, and air disinfection methods; each removal mechanism can be assigned a first-order rate constant. The pathogen concentration in well-mixed room air depends on the emission rate, the size distribution of respirable particles carrying pathogens, and the removal rate constants. The particle settling rate and the alveolar deposition fraction depend on particle size. Given these inputs plus a susceptible person's breathing rate and exposure duration to room air, an expected alveolar dosemicrois estimated. If the infectious dose is one organism, as appears to be true for tuberculosis, infection risk is estimated by the expression: R = 1-exp(-micro). Using published tuberculosis data concerning cough frequency, bacilli concentration in respiratory fluid, and die-off rate, we illustrate the model via a plausible scenario for a person visiting the room of a pulmonary tuberculosis case. We suggest that patients termed "superspreaders" or "dangerous disseminators" are those infrequently encountered persons with high values of cough and/or sneeze frequency, elevated pathogen concentration in respiratory fluid, and/or increased respirable aerosol volume per expiratory event such that their pathogen emission rate is much higher than average.
Adequate nasal air-conditioning is of greatest importance. Because detailed processes of nasal air-conditioning still are not completely understood, numerical simulations of intranasal temperature distribution and airflow patterns during inspiration and expiration were performed.
A three-dimensional model of the human nose based on computed tomography scans was reconstructed. A computational fluid dynamics application was used displaying temperature and airflow during respiration based on time-dependent boundary conditions.
Absolute air temperature and velocity values vary depending on detection site and time of detection. Areas of low velocities and turbulence show distinct changes in air temperature. The turbinate areas prove to be the main regions for heat exchange. The numerical results showed excellent comparability to our in vivo measurements.
Numerical simulation of temperature and airflow based on computational fluid dynamics is feasible providing entirely novel information and an insight into air-conditioning of the human nose.
Physiological basis of ventilatory support. Informa Health Care
- J J Marini
- A S Slutsky
Marini, J. J., & Slutsky, A. S. (1998). Physiological basis of ventilatory support. Informa Health Care.
Inhalation aerosols: Physical and biological basis for therapy Lung biology in health and disease Inhalation aerosols: Physical and biological basis for therapy Lung biology in health and disease
- A J Hickey
Hickey, A. J., (Ed.). (1996). Inhalation aerosols: Physical and biological basis for therapy. Lung biology in health and disease. New York: Marcel Dekker Inc. 6 Hickey, A. J., (Ed.). (1996). Inhalation aerosols: Physical and biological basis for therapy. Lung biology in health and disease. New York: Marcel Dekker Inc.
Inhalation aerosols: Physical and biological basis for therapy. Lung biology in health and disease
- A Hickey