Indoor air quality improvement in COVID-19 pandemic: Review

Short-term storability of volatile organic compounds in bag sampling systems under ambient conditions

Although bag sampling is a common quantification tool for volatile organic compounds (VOCs), it can serve as a major source of experimental bias, when storing even over a short duration (<24 h). To learn more about the reliability of the bag sampling method, the temporal stability of 27 VOCs (classified into five groups (i.e., aldehydes, nonpolar aromatic hydrocarbons, aliphatic carboxylic acids, phenol and methylphenols, and miscellaneous odorants) is assessed using poly-ester aluminum (PEA) bags at five intervals over a day (0.17, 1, 2, 6, and 24 h). In terms of reproducibility (e.g., relative standard error [RSEt, %]), nonpolar aromatic hydrocarbons (BTXS) exhibit the highest consistency (e.g., average RSE <1.55%). Considerable loss of VOCs is observed in the preparation of gaseous standards from a liquid phase standard when assessed by gas/liquid (G/L) ratio. Further, VOCs with lower molecular weights (e.g., propionaldehyde: 77%-94.4%) and branched molecular structures (e.g., isovaleraldehyde: 67.2%-78.9%) tend to have high G/L ratio (e.g., relative to valeraldehyde: 55.1%-66%). The overall relative recovery (RR; %) values of VOCs indicate an exponential decrease over 24 h. BTXS maintain fairly good RR values (above 94.3% at all intervals), possibly due to the nonpolar structure with uniform distribution of π electrons. In contrast, indole and skatole show the least preservation after 24 h (e.g., RR4 values of 10.9% and 24.6%, respectively) due to their highly reactive characteristics. The storability of VOCs appears to be affected by a number of variables (e.g., molecular weight, presence of ethyl branch, and time: e.g., R2 > 0.9). The results of this study offer valuable guidelines for the accurate quantification of VOC levels in air.

Distribution of COVID-19 mitigation measures by industry and work arrangement-US blood donors, May 2021-December 2021

OBJECTIVE

To describe coronavirus disease 2019 (COVID-19) mitigation measures in workplaces of employed US blood donors by industry and work arrangement.

METHODS

During May-December 2021, blood donors responded to a survey; we describe the distribution of reported workplace mitigation measures by industry and work arrangement, organized using the hierarchy of controls.

RESULTS

Of 53,433 respondents representing 21 industries, ventilation upgrades were reported by 4%-38% of respondents (overall: 20%); telework access ranged from 14%-80% (53% overall). Requiring masks (overall: 84%; range: 40%-94%), physical distancing (77%; 51%-86%), paid leave for illness (70%; 38%-87%), and encouraging vaccination (61%; 33%-80%) were common. Independent workers reported fewer mitigation measures than those in traditional employment settings.

CONCLUSIONS

Mitigation measures varied by industry and work arrangement. Some mitigation measures may be challenging to implement or irrelevant in certain industries, supporting the idea that mitigation is not a one-size-fits-all strategy.

POLICY IMPLICATIONS

Tailored strategies to mitigate workplace risks of disease transmission are vital. Strategies should rely on effective methods for identifying workplace controls (e.g., through the hierarchy of controls) and account for industry-specific characteristics and workplace environments.

An overview for monitoring and prediction of pathogenic microorganisms in the atmosphere

Corona virus disease 2019 (COVID-19) has exerted a profound adverse impact on human health. Studies have demonstrated that aerosol transmission is one of the major transmission routes of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Pathogenic microorganisms such as SARS-CoV-2 can survive in the air and cause widespread infection among people. Early monitoring of pathogenic microorganism transmission in the atmosphere and accurate epidemic prediction are the frontier guarantee for preventing large-scale epidemic outbreaks. Monitoring of pathogenic microorganisms in the air, especially in densely populated areas, may raise the possibility to detect viruses before people are widely infected and contain the epidemic at an earlier stage. The multi-scale coupled accurate epidemic prediction system can provide support for governments to analyze the epidemic situation, allocate health resources, and formulate epidemic response policies. This review first elaborates on the effects of the atmospheric environment on pathogenic microorganism transmission, which lays a theoretical foundation for the monitoring and prediction of epidemic development. Secondly, the monitoring technique development and the necessity of monitoring pathogenic microorganisms in the atmosphere are summarized and emphasized. Subsequently, this review introduces the major epidemic prediction methods and highlights the significance to realize a multi-scale coupled epidemic prediction system by strengthening the multidisciplinary cooperation of epidemiology, atmospheric sciences, environmental sciences, sociology, demography, etc. By summarizing the achievements and challenges in monitoring and prediction of pathogenic microorganism transmission in the atmosphere, this review proposes suggestions for epidemic response, namely, the establishment of an integrated monitoring and prediction platform for pathogenic microorganism transmission in the atmosphere.

The impact of digital economy on rural revitalization: Evidence from Guangdong, China

Background

Digital technology and economy have profound impact on rural revitalization and become important initiatives to promote rural development. This study analyzes the spatial effect of digital economy on rural revitalization in Guangdong, China.

Method

The entropy weight method is used to evaluate the level of rural revitalization and digital economy in 20 prefecture level cities of Guangdong province during 2011-2021. Spatial panel model is used to analyze the spatial spillover effect of digital economy on rural revitalization. Threshold model is employed to analyze the marginal effects of the digital economy on rural revitalization. Heterogeneous analysis is made by grouping the prefecture-level cities into four regions: the Pearl River Delta (PRD), the East Wing, the West Wing and the Mountainous region.

Results

Both the level of rural revitalization and digital economy development in every prefecture-level city experienced an increase during 2011-2021 and the PRD region take the lead in both the rural revitalization and digital economy. There is significant spatial spillover effect of digital economy on the rural revitalization as a whole (the coefficient is about 0.3537). However, in the regions with a low level of digital economic development, there is a negative impact (-0.1847) of the digital economy on rural revitalization; while in regions with medium or high level of digital economy, it has a significant positive effect (0.3835) on rural revitalization. The impact of digital economy on rural revitalization development is significantly greater in the PRD (0.3141), the East Wing (0.7215), the West Wing (0.5467) than in the mountainous region (0.2238).

Conclusions

There is significant spatial differentiation in the digital economy and rural revitalization. The digital economy has significant spatial spillover effect on the rural revitalization. And this effect is found out to have heterogeneous and non-linear characteristics. In order to promote rural revitalization, it is necessary to make full use of the digital economy and technology in rural areas. Besides, it is important to improve the digital skills and literary of the rural population so that the digital economy could play a greater role in rural revitalization.

Easy-to-Use MOX-Based VOC Sensors for Efficient Indoor Air Quality Monitoring

This research paper presents a case study on the application of Metal Oxide Semiconductor (MOX)-based VOC/TVOC sensors for indoor air quality (IAQ) monitoring. This study focuses on the ease of use and the practical benefits of these sensors, drawing insights from measurements conducted in a university laboratory setting. The investigation showcases the straightforward integration of MOX-based sensors into existing IAQ monitoring systems, highlighting their user-friendly features and the ability to provide precise and real-time information on volatile organic compound concentrations. Emphasizing ease of installation, minimal maintenance, and immediate data accessibility, this paper demonstrates the practicality of incorporating MOX-based sensors for efficient IAQ management. The findings contribute to the broader understanding of MOX sensor capabilities, providing valuable insights for those seeking straightforward and effective solutions for indoor air quality monitoring. This case study outlines the feasibility and benefits of utilizing MOX-based sensors in various environments, offering a promising avenue for the widespread adoption of user-friendly technologies in IAQ management.

New Methodology to Evaluate and Optimize Indoor Ventilation Based on Rapid Response Sensors

The recent pandemic increased attention to the need for appropriated ventilation and good air quality as efficient measures to achieve safe and healthy indoor air. This work provides a novel methodology for continuously evaluating ventilation in public areas using modern rapid response sensors (RRS). This methodology innovatively assesses the ventilation of a space by combining a quantitative estimation of the real air exchange in the space-obtained from CO2 experimental RRS measurements and the characteristics of and activity in the space-and indoor and outdoor RRS measurements of other pollutants, with healthy recommendations from different organisations. The methodology allows space managers to easily evaluate, in a continuous form, the appropriateness of their ventilation strategy, thanks to modern RRS measurements and direct calculations (implemented here in a web app), even in situations of full activity. The methodology improves on the existing standards, which imply the release of tracer gases and expert intervention, and could also be used to set a control system that measures continuously and adapts the ventilation to changes in indoor occupancy and activity, guaranteeing safe and healthy air in an energy-efficient way. Sample public concurrence spaces with different conditions are used to illustrate the methodology.

Direct numerical simulation of contaminant removal in presence of underfloor air distribution system

Indoor contaminant removal over 0.5 ≤ FrT ≤ 5.0, 0.5 ≤ N ≤ 5.0, and 50 ≤ Re ≤ 500 was investigated numerically, wherein FrT refers to the Froude number, N refers to the buoyancy ratio, and Re refers to the Reynolds number. As demonstrated, the ventilation effectiveness increased with increasing contaminant source intensity and air supply intensity at a constant air temperature, indicating that increase the fresh air can effectively eliminate contaminants in this case. At high air supply temperatures, the heat retention time and contaminant transport was extremely short, and the fresh air induced by strong natural convection floating lift was rapidly discharged. Additioanlly, the air supply intensity had significant effects on contaminant removal. Quantification of the ventilation effectiveness under the combined effects of air supply intensity, air supply temperature and contaminant source intensity was determined based on the results of direct numerical simulations.

Mapping COVID-19's potential infection risk based on land use characteristics: A case study of commercial activities in two Egyptian cities

The contagious COVID-19 has recently emerged and evolved into a world-threatening pandemic outbreak. After pursuing rigorous prophylactic measures two years ago, most activities globally reopened despite the emergence of lethal genetic strains. In this context, assessing and mapping activity characteristics-based hot spot regions facilitating infectious transmission is essential. Hence, our research question is: How can the potential hotspots of COVID-19 risk be defined intra-cities based on the spatial planning of commercial activity in particular? In our research, Zayed and October cities, Egypt, characterized by various commercial activities, were selected as testbeds. First, we analyzed each activity's spatial and morphological characteristics and potential infection risk based on the Centre for Disease Control and Prevention (CDCP) criteria and the Kriging Interpolation method. Then, using Google Mobility, previous reports, and semi-structured interviews, points of interest and population flow were defined and combined with the last step as interrelated horizontal layers for determining hotspots. A validation study compared the generated activity risk map, spatial COVID-19 cases, and land use distribution using logistic regression (LR) and Pearson coefficients (rxy). Through visual analytics, our findings indicate the central areas of both cities, including incompatible and concentrated commercial activities, have high-risk peaks (LR = 0.903, rxy = 0.78) despite the medium urban density of districts, indicating that urban density alone is insufficient for public health risk reduction. Health perspective-based spatial configuration of activities is advised as a risk assessment tool along with urban density for appropriate decision-making in shaping pandemic-resilient cities.

The identification environment matters: Students' social identification, perceived physical school environment, and anxiety - A cross-level interaction model

The social identity approach to health argues that well-being depends on the psychosocial circumstances of the groups to which individuals belong. However, little is known about how the average level of identification in the group - 'the identification environment' - buffers the negative health consequences of stressors. We used multilevel modelling to investigate whether identification environment in a school modified the association between the students' perceptions of the quality of their school's physical environment and their reported levels of anxiety. In two representative samples of Finnish school students (N = 678 schools/71,392 students; N = 704 schools/85,989 students), weak identification environment was related to increased anxiety. In addition, in schools where identification environment was weaker, the student level relationship between perceived physical environment and anxiety was stronger, and students were more anxious. Our results provide evidence that identification environment needs to be considered when we analyse how group membership affects well-being.

Physiological alterations and heavy metal accumulation in the transplanted lichen Pyxine cocoes (Sw.) Nyl. in Lucknow city, Uttar Pradesh

Air pollution has become a major concern due to its detrimental effects on living beings. The present study is aimed at assessing the current status of air pollution in Lucknow city using lichen transplantation technique and assesing its effect on physiology of Pyxine cocoes. The samples of P. cocoes were collected from relatively pollution-free area Malihabad and transplanted in 10 designated sites in five regions for 30 days. Various parameters such as heavy metals, chlorophyll pigments, carotenoid, chlorophyll degradation, and electrolyte conductivity were estimated in transplanted lichens. The study revealed that the concentration of all 10 heavy metals was higher in all transplanted samples than in the control sample, which was found in order of Al > Fe > Mn > Zn > Cu > Cr > Pb > Ni > Co > Cd. Among all 10 transplanted sites, the significantly increased accumulation of aluminum (5.11 to 5.47 µg L-1), iron (4.73 to 5.46 µg L-1), manganese (110.99 to 144.58 µg g-1), and zinc (87.96 to 97.40 µg g-1) was found in Charbagh, Qaisarbagh, and Alambagh sites. Further, in all samples, chlorophyll a (3.98 µg L-1), chlorophyll b (1.22 µg L-1), total chlorophyll (5.20 µg L-1), and chlorophyll degradation (0.55 µg g-1) were significantly decreased, whereas elevated levels of carotenoid (0.71 µg g-1), and electrolyte conductivity (64.99 µS cm-1), were observed. The scanning electron microscope (SEM) investigated the morphological changes in transplanted lichen samples, and significant damage to the anatomy of mycelium was found in most of the polluted site's samples, which correlated with the pollution levels. The present study clearly demonstrated that the transplanted lichen P. cocoes is an efficient bioaccumulator and bioindicator of air quality in urban environments.

Mimosa Kinetic Façade: Bio-Inspired Ventilation Leveraging the Mimosa Pudica Mechanism for Enhanced Indoor Air Quality

In light of pressing global health concerns, the significance of indoor air quality in densely populated structures has been emphasized. This research introduces the Mimosa kinetic façade, an innovative design inspired by the adaptive responsiveness of the Mimosa plant to environmental stimuli. Traditional static architectural façades often hinder natural ventilation, leading to diminished air quality with potential health and cognitive repercussions. The Mimosa kinetic façade addresses these challenges by enhancing effective airflow and facilitating the removal of airborne contaminants. This study evaluates the façade's impact on quality of life and its aesthetic contribution to architectural beauty, utilizing the biomimicry design spiral for a nature-inspired approach. Computational simulations and physical tests were conducted to assess the ventilation capacities of various façade systems, with a particular focus on settings in Bangkok, Thailand. The study revealed that kinetic façades, especially certain patterns, provided superior ventilation compared to static ones. Some patterns prioritized ventilation, while others optimized human comfort during extended stays. Notably, the most effective patterns of the kinetic façade inspired by the Mimosa demonstrated a high air velocity reaching up to 12 m/s, in contrast to the peak of 2.50 m/s in single-sided façades (traditional façades). This highlights the kinetic façade's potential to rapidly expel airborne particles from indoor spaces, outperforming traditional façades. The findings underscore the potential of specific kinetic façade patterns in enhancing indoor air quality and human comfort, indicating a promising future for kinetic façades in architectural design. This study aims to achieve an optimal balance between indoor air quality and human comfort, although challenges remain in perfecting this equilibrium.

Building parameters linked with indoor transmission of SARS-CoV-2

The rapid spread of Coronavirus Disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has emphasized the importance of understanding and adapting to the indoor remediation of transmissible diseases to decrease the risk for future pandemic threats. While there were many precautions in place to hinder the spread of COVID-19, there has also been a substantial increase of new research on SARS-CoV-2 that can be utilized to further mitigate the transmission risk of this novel virus. This review paper aims to identify the building parameters of indoor spaces that could have considerable influence on the transmission of SARS-CoV-2. The following building parameters have been identified and analyzed, emphasizing their link with the indoor transmission of SARS-CoV-2: temperature and relative humidity, temperature differences between rooms, ventilation rate and access to natural ventilation, occupant density, surface type and finish, airflow direction and speed, air stability, indoor air pollution, central air conditioning systems, capacity of air handling system and HVAC filter efficiency, edge sealing of air filters, room layout and interior design, and compartmentalization of interior space. This paper also explains the interactions of SARS-CoV-2 with indoor environments and its persistence. Furthermore, the modifications of the key building parameters have been discussed for controlling the transmission of SARS-CoV-2 in indoor spaces. Understanding the information provided in this paper is crucial to develop effective health and safety measures that will aid in infection prevention.

A comprehensive review of microbial contamination in the indoor environment: sources, sampling, health risks, and mitigation strategies

The quality of the indoor environment significantly impacts human health and productivity, especially given the amount of time individuals spend indoors globally. While chemical pollutants have been a focus of indoor air quality research, microbial contaminants also have a significant bearing on indoor air quality. This review provides a comprehensive overview of microbial contamination in built environments, covering sources, sampling strategies, and analysis methods. Microbial contamination has various origins, including human occupants, pets, and the outdoor environment. Sampling strategies for indoor microbial contamination include air, surface, and dust sampling, and various analysis methods are used to assess microbial diversity and complexity in indoor environments. The review also discusses the health risks associated with microbial contaminants, including bacteria, fungi, and viruses, and their products in indoor air, highlighting the need for evidence-based studies that can relate to specific health conditions. The importance of indoor air quality is emphasized from the perspective of the COVID-19 pandemic. A section of the review highlights the knowledge gap related to microbiological burden in indoor environments in developing countries, using India as a representative example. Finally, potential mitigation strategies to improve microbiological indoor air quality are briefly reviewed.

The effect of natural ventilation on airborne transmission of the COVID-19 virus spread by sneezing in the classroom

Since school classrooms are of vital importance due to their impact on public health in COVID-19 and similar epidemics, it is imperative to develop new ventilation strategies to reduce the risk of transmission of the virus in the classroom. To be able to develop new ventilation strategies, the effect of local flow behaviors in the classroom on the airborne transmission of the virus under the most dramatic conditions must first be determined. In this study, the effect of natural ventilation on the airborne transmission of COVID-19-like viruses in the classroom in the case of sneezing by two infected students in a reference secondary school classroom was investigated in five scenarios. Firstly, experimental measurements were carried out in the reference class to validate the computational fluid dynamics (CFD) simulation results and determine the boundary conditions. Next, the effects of local flow behaviors on the airborne transmission of the virus were evaluated for five scenarios using the Eulerian-Lagrange method, a discrete phase model, and a temporary three-dimensional CFD model. In all scenarios, immediately after sneezing, between 57 and 60.2 % of the droplets containing the virus, mostly large and medium-sized (150 μm < d < 1000 μm) settled on the infected student's desk, while small droplets continued to move in the flow field. In addition, it was determined that the effect of natural ventilation in the classroom on the travel of virus droplets in the case of Redh < 8.04 × 104 (Reynolds number, Redh=Udh/νu, dh and are fluid velocity, hydraulic diameters of the door and window sections of the class and kinematic viscosity, respectively) was negligible.

Towards the new generation of courtyard buildings as a healthy living concept for post-pandemic era

COVID-19 has laid a context for holistic research and practical approaches towards health issues in buildings. This study focuses on one particular residential building type, which is a combination of a modern apartment building with private double-oriented terraces, and a traditional courtyard building. This principle improves several aspects of healthy buildings and contributes to address indoor-outdoor interactions, daylighting, and the use of natural ventilation. The purpose of this study is to determine the factors underlying a particular type of semi-outdoor space within building forms and to explain their microclimatic behavior in buildings. One solid model and twelve porous apartment buildings with different numbers of porous sides, and terrace widths are evaluated using computational fluid dynamics. The k-ε turbulence model is adapted to simulate airflow in and around a four-story building. CFD simulations were validated against the wind-tunnel measurements. Investigations indicated that increasing the number of porous sides reduces the internal mean and maximum ages of air by -15.75 and -36.84%, which means improved ventilation performance. However, it leaves a negative trace on ventilation of the semi-outdoor spaces. Meanwhile, increasing the width of the terraces enhances the ventilation performance by reducing the mean age of air in units, courtyards, and terraces by -20%, -20%, and -9%, respectively.

Numerical study of different ventilation schemes in a classroom for efficient aerosol control

The air quality is a parameter to be controlled in order to live in a comfortable place. This paper analyzes the trajectory of aerosols exhaled into the environment in a classroom. Three scenarios are investigated; without ventilation, with natural and with mechanical ventilation. A multi-phase computational fluid study based on Eulerian-Lagrangian techniques is defined. Temperature and ambient relative humidity, as well as air velocity, direction and pressure is taken into account. For droplets evaporation, mass transfer and turbulent dispersion have been added. This work tends to be of great help in various areas, such as the field of medicine and energy engineering, aiming to show the path of aerosols dispersed in the air. The results show that the classroom with a mechanical ventilation scheme offers good results when it comes to an efficient control of aerosols. In all three cases, aerosols exhaled into the environment impregnate the front row student in the first 0.5 s. Reaching the time of 4, 2 and 1 s, in the class without ventilation, mechanical and natural ventilation, respectively, the aerosols have been already deposited on the table of the person in the first row, being exposed for longer in the case of no ventilation. Particles with a diameter of less than 20 μm are distributed throughout the classroom over a long period. The air jet injected into the interior space offers a practically constant relative humidity and a drop in temperature, slowing down the process of evaporation of the particles. In the first second, it can be seen that a mass of 0.0025 mg formed by 9 million droplets accumulates, in cases without ventilation and natural ventilation. The room with a mechanical installation accumulated 5.5 million particles of mass 0.0028 mg in the first second. The energy losses generated by natural ventilation are high compared to the other scenarios, exactly forty and twenty times more in the scenario with mechanical ventilation and without ventilation, respectively.

New ventilation design criteria for energy sustainability and indoor air quality in a post Covid-19 scenario

The Covid-19 outbreak raised great attention to the importance of indoor air quality in buildings. Even if the Covid-19 epidemic is nearing an end, all stakeholders agree that increasing outside air flow rates is beneficial for decreasing the likelihood of contagion, lowering the risk of future pandemics, and enhancing the general safety of the interior environment. Indeed, diverse concerns raised about whether the ventilation standards in place are still adequate. In this context, this research intends to assess the suitability of current ventilation standards in addressing the current pandemic scenario and to offer novel criteria and guidelines for the design and operation of HVAC systems, as well as useful guidance for the creation of future ventilation standards in a post-Covid-19 scenario. To that end, a comprehensive analysis of the ANSI/ASHRAE 62.1 is carried out, with an emphasis on its effectiveness in reducing the risk of infection. Furthermore, the efficacy of various ventilation strategies in reducing the likelihood of contagion has been investigated. Finally, because building ventilation is inextricably linked to energy consumption, the energy and economic implications of the proposed enhancements have been assessed. To carry out the described analysis, a novel method was developed that combines Building Energy Modelling (BEM) and virus contagion risk assessment. The analyses conducted produced interesting insights and criteria for ventilation system design and operation, as well as recommendations for the development of future standards.

Aerosol exchange between pressure-equilibrium rooms induced by door motion and human movement

It is now widely recognised that aerosol transport is major vector for transmission of diseases such as COVID-19, and quantification of aerosol transport in the built environment is critical to risk analysis and management. Understanding the effects of door motion and human movement on the dispersion of virus-laden aerosols under pressure-equilibrium conditions is of great significance to the evaluation of infection risks and development of mitigation strategies. This study uses novel numerical simulation techniques to quantify the impact of these motions upon aerosol transport and provides valuable insights into the wake dynamics of swinging doors and human movement. The results show that the wake flow of an opening swinging door delays aerosol escape, while that of a person walking out entrains aerosol out of the room. Aerosol escape caused by door motion mainly happens during the closing sequence which pushes the aerosols out. Parametric studies show that while an increased door swinging speed or human movement speed can enhance air exchange across the doorway, the cumulative aerosol exchange across the doorway is not clearly affected by the speeds.

Assessment of natural ventilation strategy to decrease the risk of COVID 19 infection at a rural elementary school

Natural ventilation in low-budget elementary schools is the main focus to ensure the health and comfort of its occupants, specifically when looking at the global pandemic related to SARS-COV-2. This paper presents an experimental and novel study of natural ventilation in a public elementary school (Los Zumacales), with a particularly low economic budget. The study was carried out during the winter months of the Covid 19 pandemic. The school is located in the rural area of Castilla y León (North-Western Spain) far from high traffic roads. In this study, a methodology of measuring CO2 concentration was applied in nine classrooms in a school. The experimental study shows the level of natural ventilation in each classroom, expressed in Air Changes per Hour (ACH), using the Decay CO2 concentration method. The method is proven by comparing the experimental values of the obtained ACH with those determined by the most powerful methods to achieve appropriate ventilation levels. Thus, ensuring health protection protocol in rural schools, against the COVID 19 pandemic. Harvard guide and Spanish regulations (RITE), two widely recognized methods have been used together with the experimentally obtained standard by Rey et al. Only one classroom showed a value lower than 3 indicating poor ventilation. In this study, the degree of thermal comfort in the nine classrooms were also analyzed according to the EN15251 standard. An average indoor temperature of approximately 19 °C was obtained, and the relative humidity was stable and correct according to Spanish regulations. In addition, the risk of infection in each classroom was estimated following the international method recommended by the federation of European Heating, Ventilation, and Air Conditioning Associations (REHVA). The probability of infection in all the cases studied was less than 14%. Therefore, this study provides a strong response against infections illnesses, such as Covid 19, in educational buildings where economic budgets of their facilities are low in both, maintenance and investment.

Slack in the infrastructure of intensive care units: resilience management in the post-pandemic era

BACKGROUND

Although slack is an asset to resilient hospitals, it is usually explicitly discussed only in terms of the quantity and quality of beds and staff. This paper expands this view by addressing slack in four infrastructures of intensive care units (ICUs) (physical space, electricity supply, oxygen supply, and air treatment) during the COVID pandemic.

METHODS

The study occurred in a leading private hospital in Brazil, aiming at the identification of slack in four units originally designed as ICUs and two units adapted as ICUs. Data collection was based on 12 interviews with healthcare professionals, documents, and comparison between infrastructures and regulatory requirements.

RESULTS

Twenty-seven instantiations of slack were identified, with several indications that the adapted ICUs did not provide infrastructure conditions as good as the designed ones. Findings gave rise to five propositions addressing: relationships intra and inter infrastructures; the need for adapted ICUs that match as closely as possible the designed ICUs; the consideration of both clinical and engineering perspectives in design; and the need for the revision of some requirements of the Brazilian regulations.

CONCLUSIONS

Results are relevant to both the designers of the infrastructures and to the designers of clinical activities as these must take place in fit-for-purpose workspaces. Top management might also benefit as they are the ultimate responsible for decision-making on whether or not to invest in slack. The pandemic dramatically demonstrated the value of investing in slack resources, creating momentum for this discussion in health services.

Human personal air pollution clouds in a naturally ventilated office during the COVID-19 pandemic

Personal cloud, termed as the difference in air pollutant concentrations between breathing zone and room sites, represents the bias in approximating personal inhalation exposure that is linked to accuracy of health risk assessment. This study performed a two-week field experiment in a naturally ventilated office during the COVID-19 pandemic to assess occupants' exposure to common air pollutants and to determine factors contributing to the personal cloud effect. During occupied periods, indoor average concentrations of endotoxin (0.09 EU/m³), TVOC (231 μg/m³), CO₂ (630 ppm), and PM₁₀ (14 μg/m³) were below the recommended limits, except for formaldehyde (58 μg/m³). Personal exposure concentrations, however, were significantly different from, and mostly higher than, concentrations measured at room stationary sampling sites. Although three participants shared the same office, their personal air pollution clouds were mutually distinct. The mean personal cloud magnitude ranged within 0-0.05 EU/m³, 35-192 μg/m³, 32-120 ppm, and 4-9 μg/m³ for endotoxin, TVOC, CO₂, and PM₁₀, respectively, and was independent from room concentrations. The use of hand sanitizer was strongly associated with an elevated personal cloud of endotoxin and alcohol-based VOCs. Reduced occupancy density in the office resulted in more pronounced personal CO₂ clouds. The representativeness of room stationary sampling for capturing dynamic personal exposures was as low as 28% and 5% for CO₂ and PM₁₀, respectively. The findings of our study highlight the necessity of considering the personal cloud effect when assessing personal exposure in offices.

The Nexus Between COVID-19 Factors and Air Pollution

Background and Objective

There have been significant effects of the current coronavirus-19 (COVID-19) infection outbreak on many facets of everyday life, particularly the environment. Despite the fact that a number of studies have already been published on the topic, an analysis of those studies' findings on COVID-19's effects on environmental pollution is still lacking. The goal of the research is to look into greenhouse gas emissions and air pollution in Bangladesh when COVID-19 is under rigorous lockdown. The specific drivers of the asymmetric relationship between air pollution and COVID-19 are being investigated.

Methods

The nonlinear relationship between carbon dioxide ( C O 2 ) emissions, fine particulate matter ( P M 2 . 5 ) , and COVID-19, as well as its precise components, are also being investigated. To examine the asymmetric link between COVID-19 factors on C O 2 emissions and P M 2 . 5 , we employed the nonlinear autoregressive distributed lag (NARDL) model. Daily positive cases and daily confirmed death by COVID-19 are considered the factors of COVID-19, with lockdown as a dummy variable.

Results

The bound test confirmed the existence of long-run and short-run relationships between variables. Bangladesh's strict lockdown, enforced in reaction to a surge of COVID-19 cases, reduced air pollution and dangerous gas emissions, mainly C O 2 , according to the dynamic multipliers graph.

Artificial intelligence-based prediction of indoor bioaerosol concentrations from indoor air quality sensor data

Exposure to bioaerosols in indoor environments, especially public venues that have a high occupancy and poor ventilation, is a serious public health concern. However, it remains challenging to monitor and determine real-time or predict near-future concentrations of airborne biological matter. In this study, we developed artificial intelligence (AI) models using physical and chemical data from indoor air quality sensors and physical data from ultraviolet light-induced fluorescence observations of bioaerosols. This enabled us to effectively estimate the bioaerosol (bacteria-, fungi- and pollen-like particle) and 2.5-µm and 10-µm particulate matter (PM_2.5 and PM₁₀) on a real-time and near-future (≤60 min) basis. Seven AI models were developed and evaluated using measured data from an occupied commercial office and a shopping mall. A long short-term memory model required a relatively short training time and gave the highest prediction accuracy of ∼ 60 %-80 % for bioaerosols and ∼ 90 % for PM on the testing and time series datasets from the two venues. This work demonstrates how AI-based methods can leverage bioaerosol monitoring into predictive scenarios that building operators can use for improving indoor environmental quality in near real-time.

Multi-camera BEV video-surveillance system for efficient monitoring of social distancing

The current sanitary emergency situation caused by COVID-19 has increased the interest in controlling the flow of people in indoor infrastructures, to ensure compliance with the established security measures. Top view camera-based solutions have proven to be an effective and non-invasive approach to accomplish this task. Nevertheless, current solutions suffer from scalability problems: they cover limited range areas to avoid dealing with occlusions and only work with single camera scenarios. To overcome these problems, we present an efficient and scalable people flow monitoring system that relies on three main pillars: an optimized top view human detection neural network based on YOLO-V4, capable of working with data from cameras at different heights; a multi-camera 3D detection projection and fusion procedure, which uses the camera calibration parameters for an accurate real-world positioning; and a tracking algorithm which jointly processes the 3D detections coming from all the cameras, allowing the traceability of individuals across the entire infrastructure. The conducted experiments show that the proposed system generates robust performance indicators and that it is suitable for real-time applications to control sanitary measures in large infrastructures. Furthermore, the proposed projection approach achieves an average positioning error below 0.2 meters, with an improvement of more than 4 times compared to other methods.

Aero-manufacture of nanobulges for an in-place anticoronaviral on air filters

The interest in removing contagious viruses from indoor air using ventilation and filtration systems is increasing rapidly because people spend most of the day indoors. The development of an effective platform to regenerate the antiviral function of air filters during use and safe abrogation of used filters containing infectious viruses is a challenging task, because an on-demand safe-by-design manufacture system is essential for in-place antiviral coatings, but it has been rarely investigated. With these considerations, an electrically operable dispenser was prepared for decorating continuous ultrafine Fe-Zn, Fe-Ag, or Fe-Cu particles (<5 nm) onto SiO₂ nanobeads (ca. 130 nm) to form nanobulges (i.e., nanoroughness for engaging coronavirus spikes) in the aerosol state for 3 min direct deposition on the air filter surfaces. The resulting nanobulges were exposed to human coronaviruses (HCoV; surrogates of SARS-CoV-2) to assess antiviral function. The results were compared with similar-sized individual Zn, Ag, and Cu particles. The nanobulges exhibited comparable antiviral activity to Zn, Ag, and Cu particles while retaining biosafety in both in vitro and in vivo models because of the significantly smaller metallic fractions. This suggests that the bimetallic bulge structures generate reactive oxygen species and Fenton-mediated hydroxyl radicals for inactivating HCoV.

Monitoring indoor air quality using smart integrated gas sensor module (IGSM) for improving health in COPD patients

Technology advancement, industrialisation, and globalisation have been significant reasons for air pollution outdoors and indoors. It may surprise us that we spend about 80% of our time indoors breathing toxic, stale, polluted air, making us sluggish and fretful. In contrast to outdoor air, indoor air does not recycle consistently. It traps and builds pollutants from wood and coal stoves, furniture and building materials, paints and solvents, cigarette smoke, and cleaning supplies. The prolonged exposure to these hidden pollutants can prompt respiratory disorders such as lung disease, pneumonitis, asthma, pulmonary hypertension, and chronic obstructive pulmonary disease (COPD). It is enduring and is not curable, which has been a threat to humanity for ages. COPD's major cause is airborne particulate matter and other toxic compounds emitted from indoor and outdoor sources. Outdoor air pollution can be controlled only by acquiring changes in the vast population, wherein for indoor, every individual may create a major impact on improving air purity, thereby promoting health. The proposed design model for monitoring indoor air quality was tested in a normal and stimulating environment where we live. Parameters tested included temperature, humidity, amount of PM2.5, and the concentration of CO, CO₂, and NH₃. These parameters were monitored for five to 6 h per day for 8 days. Results indicate that the total air quality lies in the moderate range. Further study will be helpful to utilise this module as an effective Indoor air quality (IAQ) monitoring system. HIGHLIGHTS: • A simple, effective, inexpensive integrated gas sensor module (IGSM) has been proposed in this study to monitor the indoor air quality index (IAQI). • Indoor air quality was tested in a normal and stimulating environment for 8 days. • The integrated gas sensor module (IGSM) was composed of sensors in series, and the outputs for the respective parameter were measured easily. • Among the parameters tested, CO and PM2.5 lie in the moderate range, while other pollutants within the normal range reveal that the tested air quality is moderate.

Indoor air quality in day-care centres: a global review

A healthy indoor environment is critical for children due to the severe effect of poor indoor air quality (IAQ) on their overall well-being. Day-care centres (DCCs) are important indoor microenvironments for children apart from their homes. Therefore, monitoring IAQ in this microenvironment is vital because of the vulnerability of the occupants. This review gives a global overview of the predominant indoor chemical pollutant levels monitored in DCCs, compares their concentration with available regulations for IAQ, evaluates the sources and health risk effects of chemical pollutants and proposes strategies for enhancing IAQ in DCCs. Thirty-seven (37) articles were used based on specific stated inclusion and exclusion criteria. Continents like Europe and Asia have the most published studies in indoor DCCs. The decreasing trend of pollutants examined in most studies include particulate matter > carbon dioxide > formaldehyde > carbon monoxide > total volatile organic compounds > volatile organic compounds > nitrogen dioxide > ozone > benzene > sulphur dioxide = radon. Particulate matter in the size and mass concentration range of PM₁₀ (0.116-1920.71 μg/m³) > PM_2.5 (0.279.2-260.74 μg/m³) was the most investigated pollutant. While nitrogen dioxide, radon and carbon monoxide were consistent with the existing national and international reference values for IAQ across the continents, exceedances occurred in other pollutants. The limited number of indoor chemical pollutant studies suggests the need for more comprehensive studies on IAQ in DCC globally. Further studies should highlight the availability of low-cost sensors and mobile analytical equipment that will promote affordable ground-level data accessibility.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11869-023-01320-5.

Thermodynamic Analysis of an Experimental Model of a Solar-Heat Supply System

In this study, the problem of the operability of the solar-heat supply system in the cold region of Kazakhstan receiving minimal solar radiation was studied. The importance of this study lies in the question of how a dual-circuit solar installation can work for productivity in the northern regions of Kazakhstan. In the course of the study, an efficiency reduced from the energy efficiency increased by using a transparent glazed window reduced the supply of coolant into the pipe. Cold liquid heat enters the resulting stream, heat transfer increases, and the intermediate walls heat up. In this study, a method was used to determine the thermal characteristics of a glazed flat collector, which contains a brief and accurate description. From the results obtained, it can be concluded that the effectiveness of 2.40 and 2.53 was recognized in this study. It was also investigated that the thermal capacity of the solar collector depends on the thickness of the absorbing layer. Having conducted this experimental study, we were convinced that it is reliable for the northern regions of Kazakhstan.

A new filterless indoor air purifier for particulate matter and bioaerosol based on heterogeneous condensation

Using an indoor air purifier is an important solution for improving indoor air quality and protecting people from the harmful effects of air pollution on their health. The filter air purifiers can remove particulate matter including bioaerosols, but their filter media can cause secondary pollution. To fulfill this need, a new filterless indoor air purifier, the Cloud-Air-Purifying (CAP) air purifier, is presented in this study. Using heterogeneous condensation and supergravity technology, the CAP air purifier grows and collects fine particles, while rapidly disinfecting bioaerosols with chemical disinfection and ultraviolet (UV) disinfection. Furthermore, the purifying performance of the CAP air purifier was tested in a simulated cabin. The results showed the clean air delivery rate (CADR) of the CAP air purifier was approximately 150 m³/h, and the effective coefficient was 0.93. The CAP air purifier was highly efficient in purifying fine particulate matter, 93% for PM₁₀ and 91% for particle size of 0.5-1 μm in 60 min, which was 13-58 times more than natural decay. The reason for the efficient removal of fine particles is that they can condense and grow in water vapor supersaturated environment and be collected in a supergravity field. Moreover, the CAP air purifier has significant bactericidal effects on bioaerosols. It achieved a disinfection efficiency of 99.99997% by decreasing bioaerosols from 10⁸ CFU/m³ to less than 30 CFU/m³ in only 20 min when particle purification in combination with UV disinfection and disinfectant (ClO₂). Furthermore, ClO₂ release concentrations, noise, and power consumption were investigated for application purposes, with results showing that they were within acceptable limits. The study presents an innovative idea and design for preventing airborne microorganisms and particulate matter through heterogeneous condensation technology.

Antimicrobial and mechanical properties of functionalized textile by nanoarchitectured photoinduced Ag@polymer coating

The control of microbial proliferation is a constant battle, especially in the medical field where surfaces, equipment, and textiles need to be cleaned on a daily basis. Silver nanoparticles (AgNPs) possess well-documented antimicrobial properties and by combining them with a physical matrix, they can be applied to various surfaces to limit microbial contamination. With this in mind, a rapid and easy way to implement a photoinduced approach was investigated for textile functionalization with a silver@polymer self-assembled nanocomposite. By exposing the photosensitive formulation containing a silver precursor, a photoinitiator, and acrylic monomers to a UV source, highly reflective metallic coatings were obtained directly on the textile support. After assessing their optical and mechanical properties, the antimicrobial properties of the functionalized textiles were tested against Escherichia coli (E. coli) and Candida albicans (C. albicans) strains. In addition to being flexible and adherent to the textile substrates, the nanocomposites exhibited remarkable microbial growth inhibitory effects.

Review of an intelligent indoor environment monitoring and management system for COVID-19 risk mitigation

The coronavirus disease (COVID-19) outbreak has turned the world upside down bringing about a massive impact on society due to enforced measures such as the curtailment of personal travel and limitations on economic activities. The global pandemic resulted in numerous people spending their time at home, working, and learning from home hence exposing them to air contaminants of outdoor and indoor origins. COVID-19 is caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which spreads by airborne transmission. The viruses found indoors are linked to the building's ventilation system quality. The ventilation flow in an indoor environment controls the movement and advection of any aerosols, pollutants, and Carbon Dioxide (CO2) created by indoor sources/occupants; the quantity of CO2 can be measured by sensors. Indoor CO2 monitoring is a technique used to track a person's COVID-19 risk, but high or low CO2 levels do not necessarily mean that the COVID-19 virus is present in the air. CO2 monitors, in short, can help inform an individual whether they are breathing in clean air. In terms of COVID-19 risk mitigation strategies, intelligent indoor monitoring systems use various sensors that are available in the marketplace. This work presents a review of scientific articles that influence intelligent monitoring development and indoor environmental quality management system. The paper underlines that the non-dispersive infrared (NDIR) sensor and ESP8266 microcontroller support the development of low-cost indoor air monitoring at learning facilities.

Field investigation of the heat stress in outdoor of healthcare workers wearing personal protective equipment in South China

Since the advent of coronavirus disease 2019 (COVID-19), healthcare workers (HCWs) wearing personal protective equipment (PPE) has become a common phenomenon. COVID-19 outbreaks overlap with heat waves, and healthcare workers must unfortunately wear PPE during hot weather and experience excessive heat stress. Healthcare workers are at risk of developing heat-related health problems during hot periods in South China. The investigation of thermal response to heat stress among HCWs when they do not wear PPE and when they finish work wearing PPE, and the impact of PPE use on HCWs' physical health were conducted. The field survey were conducted in Guangzhou, including 11 districts. In this survey, HCWs were invited to answer a questionnaire about their heat perception in the thermal environment around them. Most HCWs experienced discomfort in their back, head, face, etc., and nearly 80% of HCWs experienced "profuse sweating." Up to 96.81% of HCWs felt "hot" or "very hot." The air temperature had a significant impact on thermal comfort. Healthcare workers' whole thermal sensation and local thermal sensation were increased significantly by wearing PPE and their thermal sensation vote (TSV) tended towards "very hot." The adaptive ability of the healthcare workers would decreased while wearing PPE. In addition, the accept range of the air temperature (T _a) were determined in this investigation. Graphical Abstract.

Event-Specific Transmission Forecasting of SARS-CoV-2 in a Mixed-Mode Ventilated Office Room Using an ANN

The emerging novel variants and re-merging old variants of SARS-CoV-2 make it critical to study the transmission probability in mixed-mode ventilated office environments. Artificial neural network (ANN) and curve fitting (CF) models were created to forecast the R-Event. The R-Event is defined as the anticipated number of new infections that develop in particular events occurring over the course of time in any defined space. In the spring and summer of 2022, real-time data for an office environment were collected in India in a mixed-mode ventilated office space in a composite climate. The performances of the proposed CF and ANN models were compared with respect to traditional statistical indicators, such as the correlation coefficient, RMSE, MAE, MAPE, NS index, and a20-index, in order to determine the merit of the two approaches. Thirteen input features, namely the indoor temperature (TIn), indoor relative humidity (RHIn), area of opening (AO), number of occupants (O), area per person (AP), volume per person (VP), CO2 concentration (CO2), air quality index (AQI), outer wind speed (WS), outdoor temperature (TOut), outdoor humidity (RHOut), fan air speed (FS), and air conditioning (AC), were selected to forecast the R-Event as the target. The main objective was to determine the relationship between the CO2 level and R-Event, ultimately producing a model for forecasting infections in office building environments. The correlation coefficients for the CF and ANN models in this case study were 0.7439 and 0.9999, respectively. This demonstrates that the ANN model is more accurate in R-Event prediction than the curve fitting model. The results show that the proposed ANN model is reliable and significantly accurate in forecasting the R-Event values for mixed-mode ventilated offices.

Application of Electrospun Water-Soluble Synthetic Polymers for Multifunctional Air Filters and Face Masks

The worsening of air quality is an urgent human health issue of modern society. The outbreak of COVID-19 has made the improvement of air quality even more imperative, both for the general achievement of major health gains and to reduce the critical factors in the transmission of airborne diseases. Thus, the development of solutions for the filtration of airborne pollutants is pivotal. Electrospinning has gained wide attention as an effective fabrication technique for preparing ultrafine fibers which are specifically tailored for air filtration. Nevertheless, the utilization of harmful organic solvents is the major barrier for the large-scale applicability of electrospinning. The use of water-soluble synthetic polymers has attracted increasing attention as a 'green' solution in electrospinning. We reported an overview of the last five years of the scientific literature on the use of water-soluble synthetic polymers for the fabrication of multifunctional air filters layers. Most of recent studies have focused on polyvinyl alcohol (PVA). Various modifications of electrospun polymers have been also described. The use of water-soluble synthetic polymers can contribute to the scalability of electrospinning and pave the way to innovative applications. Further studies will be required to fully harness the potentiality of these 'greener' electrospinning processes.

Occupancy-aided ventilation for airborne infection risk control: Continuously or intermittently reduced occupancies?

Ventilation is an important engineering measure to control the airborne infection risk of acute respiratory diseases, e.g., Corona Virus Disease 2019 (COVID-19). Occupancy-aided ventilation methods can effectively improve the airborne infection risk control performance with a sacrifice of decreasing working productivity because of the reduced occupancy. This study evaluates the effectiveness of two occupancy-aided ventilation methods, i.e., the continuously reduced occupancy method and the intermittently reduced occupancy method. The continuously reduced occupancy method is determined by the steady equation of the mass conservation law of the indoor contaminant, and the intermittently reduced occupancy method is determined by a genetic algorithm-based optimization. A two-scenarios-based evaluation framework is developed, i.e., one with targeted airborne infection risk control performance (indicated by the mean rebreathed fraction) and the other with targeted working productivity (indicated by the accumulated occupancy). The results show that the improvement in the airborne infection risk control performance linearly and quadratically increases with the reduction in the working productivity for the continuously reduced occupancy method and the intermittently reduced occupancy method respectively. At a given targeted airborne infection risk control performance, the intermittently reduced occupancy method outperforms the continuously reduced occupancy method by improving the working productivity by up to 92%. At a given targeted working productivity, the intermittently reduced occupancy method outperforms the continuously reduced occupancy method by improving the airborne infection risk control performance by up to 38%.

Analyzing the spatio-temporal directions of air pollutants for the initial wave of Covid-19 epidemic over Bangladesh: Application of satellite imageries and Google Earth Engine

One of the most critical issues for city viability and global health is air quality. The shutdown interval for the COVID-19 outbreaks has turned into an ecological experiment, allowing researchers to explore the influence of human/industrial operations on air quality. In this study, we have observed and examined the spatial pattern of air pollutants, specifically CO, NO₂, SO₂, O3 as well as AOD Over Bangladesh. For that reason, the timeline was chosen from March 2019 to October 2020 (before and during the first surge of COVID-19). The full analysis has been performed in Google Earth Engine (GEE). The findings showed that, CO, SO₂, and AOD levels dropped significantly, but SO₂ dropped slowly and O₃ levels were similar, with marginally greater quantities in some areas during the lockdown than in 2019. During the shutdown, the association involving airborne pollutants and weather parameters (temperature and rainfall) revealed that rainfall and temperature were directly associated with air pollutants. COVID-19 mortality had a high positive connection with NO₂ (R² = 0.145; r = 0.38) and AOD (R² = 0.17; r = 0.412). It is also found that various air impurities concentration has a strong relationship with Covid death. It would help the policymakers and officials to gain a better understanding of the sources of atmospheric emissions to develop a substantial proof of short- and long-term mitigation ways to enhance air quality and reduce the associated disease and disability burden.

COVID-19 Contagion Risk Estimation Model for Indoor Environments

COVID-19 is an infectious disease mainly transmitted through aerosol particles. Physical distancing can significantly reduce airborne transmission at a short range, but it is not a sufficient measure to avoid contagion. In recent months, health authorities have identified indoor spaces as possible sources of infection, mainly due to poor ventilation, making it necessary to take measures to improve indoor air quality. In this work, an accurate model for COVID-19 contagion risk estimation based on the Wells-Riley probabilistic approach for indoor environments is proposed and implemented as an Android mobile App. The implemented algorithm takes into account all relevant parameters, such as environmental conditions, age, kind of activities, and ventilation conditions, influencing the risk of contagion to provide the real-time probability of contagion with respect to the permanence time, the maximum allowed number of people for the specified area, the expected number of COVID-19 cases, and the required number of Air Changes per Hour. Alerts are provided to the user in the case of a high probability of contagion and CO2 concentration. Additionally, the app exploits a Bluetooth signal to estimate the distance to other devices, allowing the regulation of social distance between people. The results from the application of the model are provided and discussed for different scenarios, such as offices, restaurants, classrooms, and libraries, thus proving the effectiveness of the proposed tool, helping to reduce the spread of the virus still affecting the world population.

Water-based air purifier with ventilation fan system: a novel approach for cleaning indoor/outdoor transitional air during the pandemic

Abstract

This article presents the design and fabrication of an air purifier that uses a water-based technique to clean indoor/outdoor transitional air to provide a low-tech air purifier against the annual smog crisis and the ongoing COVID-19 pandemic. The air purifier was designed and built. All tests were conducted in a closed room as well as a semi-outdoor area. Particle sizes of PM0.3, 0.5, 1.0, 3.0, 5.0, and 10 μm (particle/m³) were measured at an air inlet, air outlet, 2 m from an air inlet, and 4 m from an air outlet after 0, 5, 10, 15, and 20 min of air treatment, respectively, as well as CO₂ levels and relative humidity (RH). The average airflow rate was also measured. When compare to 0 min, all parameters, except semi-outdoor PM0.3 and CO₂ levels, tend to decrease in both indoor and semi-outdoor conditions. When measure by total airflow specification of a dual ventilation fan, the average airflow rate at an air outlet is reduced by 20 times.

Article Highlights

Design and fabrication of a water-based air purifier.

A low-tech air purifier helping to protect against the annual smog crisis and the ongoing COVID-19 pandemic.

The novel water-based air purifier effectively traps air particles ranging in size from 0.5 to 10 µm.

A review of strategies and their effectiveness in reducing indoor airborne transmission and improving indoor air quality

Airborne transmission arises through the inhalation of aerosol droplets exhaled by an infected person and is now thought to be the primary transmission route of COVID-19. Thus, maintaining adequate indoor air quality levels is vital in mitigating the spread of the airborne virus. The cause-and-effect flow of various agents involved in airborne transmission of viruses has been investigated through a systematic literature review. It has been identified that the airborne virus can stay infectious in the air for hours, and pollutants such as particulate matter (PM10, PM2.5), Nitrogen dioxide (NO2), Sulphur dioxide (SO2), Carbon monoxide (CO), Ozone (O3), Carbon dioxide (CO2), and Total Volatile Organic Compounds (TVOCs) and other air pollutants can enhance the incidence, spread and mortality rates of viral disease. Also, environmental quality parameters such as humidity and temperature have shown considerable influence in virus transmission in indoor spaces. The measures adopted in different research studies that can curb airborne transmission of viruses for an improved Indoor Air Quality (IAQ) have been collated for their effectiveness and limitations. A diverse set of building strategies, components, and operation techniques from the recent literature pertaining to the ongoing spread of COVID-19 disease has been systematically presented to understand the current state of techniques and building systems that can minimize the viral spread in built spaces This comprehensive review will help architects, builders, realtors, and other organizations improve or design a resilient building system to deal with COVID-19 or any such pandemic in the future.

Investigation of pre and post environmental impact of the lockdown (COVID-19) on the water quality of the Capibaribe and Tejipió rivers, Recife metropolitan region, Brazil

The coronavirus pandemic has seriously affected human health, although some improvements on environmental indexes have temporarily occurred, due to changes on socio-cultural and economic standards. The objective of this study was to evaluate the impacts of the coronavirus and the influence of the lockdown associated with rainfall on the water quality of the Capibaribe and Tejipió rivers, Recife, Northeast Brazil, using cloud remote sensing on the Google Earth Engine (GEE) platform. The study was carried out based on eight representative images from Sentinel-2. Among the selected images, two refer to the year 2019 (before the pandemic), three refer to 2020 (during a pandemic), two from the lockdown period (2020), and one for the year 2021. The land use and land cover (LULC) and slope of the study region were determined and classified. Water turbidity data were subjected to descriptive and multivariate statistics. When analyzing the data on LULC for the riparian margin of the Capibaribe and Tejipió rivers, a low permanent preservation area was found, with a predominance of almost 100% of the urban area to which the deposition of soil particles in rivers are minimal. The results indicated that turbidity values in the water bodies varied from 6 mg. L-1 up to 40 mg. L-1. Overall, the reduction in human-based activities generated by the lockdown enabled improvements in water quality of these urban rivers.

Deep visual social distancing monitoring to combat COVID-19: A comprehensive survey

Since the start of the COVID-19 pandemic, social distancing (SD) has played an essential role in controlling and slowing down the spread of the virus in smart cities. To ensure the respect of SD in public areas, visual SD monitoring (VSDM) provides promising opportunities by (i) controlling and analyzing the physical distance between pedestrians in real-time, (ii) detecting SD violations among the crowds, and (iii) tracking and reporting individuals violating SD norms. To the authors' best knowledge, this paper proposes the first comprehensive survey of VSDM frameworks and identifies their challenges and future perspectives. Typically, we review existing contributions by presenting the background of VSDM, describing evaluation metrics, and discussing SD datasets. Then, VSDM techniques are carefully reviewed after dividing them into two main categories: hand-crafted feature-based and deep-learning-based methods. A significant focus is paid to convolutional neural networks (CNN)-based methodologies as most of the frameworks have used either one-stage, two-stage, or multi-stage CNN models. A comparative study is also conducted to identify their pros and cons. Thereafter, a critical analysis is performed to highlight the issues and impediments that hold back the expansion of VSDM systems. Finally, future directions attracting significant research and development are derived.

Energy, economic, and environmental impacts of enhanced ventilation strategies on railway coaches to reduce Covid-19 contagion risks

In the last years, the Covid-19 outbreak raised great awareness about ventilation system performance in confined spaces. Specifically, the heating, ventilation, and air conditioning system design and operating parameters, such as air change per hour, air recirculation ratio, filtration device performance, and vents location, play a crucial role in reducing the spread of viruses, moulds, bacteria, and general pollutants. Concerning the transport sector, due to the impracticability of social distancing, and the relatively loose requirements of ventilation standards, the SARS-COV-19 outbreak brought a reduction of payload (up to 50%) for different carriers. Specifically, this has been particularly severe for the railway sector, where train coaches are typically characterized by relatively elevated occupancy and high recirculation ratios. In this framework, to improve the Indoor Air Quality and reduce the Covid-19 contagion risk in railway carriages, the present paper investigates the energy, economic and environmental feasibility of diverse ventilation strategies. To do so, a novel dynamic simulation tool for the complete dynamic performance investigation of trains was developed in an OpenStudio environment. To assess the Covid-19 contagion risk connected to the investigated scenarios, the Wells-Riley model has been adopted. To prove the proposed approach's capabilities and show the Covid-19 infection risk reduction potentially achievable by varying the adopted ventilation strategies, a suitable case study related to an existing medium-distance train operating in South/Central Italy is presented. The conducted numerical simulations return interesting results providing also useful design criteria.

Identifying behavior of long-distance virus transmission and mitigation performance from a COVID-19 outbreak of a daycare center

During the last two years, hundreds of millions of people in the world have been infected with SARS-CoV-2 due to recurrent waves and closed spaces. Daycare centers are critical infrastructures that cannot be replaced, even during the COVID-19 period. However, the existing settings in daycare centers may pose risks of inevitable close contact between teachers and children, as well as fomite and airborne transmission during care hours. Therefore, reinforced mitigation strategies have been applied in daycare centers to reduce potential indoor virus transfer in many countries. However, numerous outbreaks of COVID-19 have been reported in daycare centers. Therefore, in this study, researchers focused on the risk and behavior of long-distance virus transmission based on the detected viruses on air purifier filter sampling in a daycare center outbreak in Korea. Various experiments of possible situations were conducted in nursing rooms based on field interviews. The experiments monitored the long-distance transmission behavior of aerosol-sized particles and visualized particle behavior at the daycare center. The results of this study revealed that long-distance virus transmission is possible under the current settings in the daycare center, and flush-out can be an important countermeasure with reinforced ventilation methods to prevent potential airborne spread in the daycare center. The results of air purifiers represented that air purifiers should be properly installed and operated in the daycare center to prevent airborne virus spread by airflow during occupied hours. The findings of this study will contribute to the understanding of airborne virus risk and the development of customized virus measures for daycare centers.

Sustainable solutions for indoor pollution abatement during COVID phase: A critical study on current technologies & challenges

The appearance of the contagious virus COVID-19, several revelations and environmental health experts punctually predicted the possibly disastrous public health complications of coexisting catching and airborne contamination-arbitrated disease. But much attention has been given on the outdoor-mediated interactions. Almost 3.8 million premature deaths occur every year globally due to the illness from indoor air pollution. Considering the human staying longer span indoors due to restricted human activities or work from home, the indoor air quality (IAQ) might show prominent role for individual health life. Currently, the Environmental Protection Agency (EPA) ensures no regulation of indoor airborne pollution. Herein, the paper underlines the common bases of indoor air pollution, poor IAQ, and impacts of the aerosolized airborne particles on the human health. In order to address these challenges and collective contagion events in indoor environment, several emerging control techniques and preventive sustainable solutions are suggested. By this, more innovations need to be investigated in future to measure the impact of indoor air pollution on individual health.

Effectiveness of air-purifying devices and measures to reduce the exposure to bioaerosols in school classrooms

The SARS-CoV-2 pandemic, which suddenly appeared at the beginning of 2020, revealed our knowledge deficits in terms of ventilation and air pollution control. It took many weeks to realize that aerosols are the main route of transmission. The initial attempt to hold back these aerosols through textile masks seemed almost helpless, although there is sufficient knowledge about the retention capacity of fabric filters for aerosols. In the absence of a sufficient number of permanently installed heating, ventilation, and air conditioning systems, three main approaches are pursued: (a) increasing the air exchange rate by supplying fresh air, (b) using mobile air purifiers, and (c) disinfection by introducing active substances into the room air. This article discusses the feasibility of these different approaches critically. It also provides experimental results of air exchange measurements in a school classroom that is equipped with a built-in fan for supplying fresh air. With such a fan and a window tilted at the appropriate distance, an air exchange rate of 5/h can be set at a low power level and without any significant noise pollution. Heat balance calculations show that no additional heat exchanger is necessary in a normal classroom with outside temperatures above 10°C. Furthermore, a commercial mobile air purifier is studied in a chamber and a test room setup in order to examine and evaluate the efficiency of such devices against viable viruses under controlled and realistic conditions. For this purpose, bacteriophages of the type MS2 are used. Both window ventilation and air purifiers were found to be suitable to reduce the concentration of phages in the room.

Analysis of the impact of a fresh air system on the indoor environment in office buildings

This study conducted objective physical tests and subjective questionnaire surveys related to the operation of a fresh air system in an office building in Beijing before the outbreak of the coronavirus disease 2019 (COVID-19). The long-term tests on indoor environmental parameters included air temperature, relative air humidity, air velocity, CO₂ concentration, PM_2.5 concentration, and fresh air volume, and the questionnaire surveyed the satisfaction of office workers in the indoor environment. The results showed that the indoor environmental parameters conformed to the values specified in relevant design standards; however, the satisfaction with the indoor environmental parameters was generally low. The probability of infection of indoor personnel with the virus causing COVID-19 under two existing fresh air system operation modes was calculated and compared, and it was less than 5%. A gray correlation analysis of the measured data with the questionnaire results identified indoor air temperature and quality as the main factors affecting the subjective satisfaction, which was consistent with the results of the questionnaire analysis. A new operation and maintenance method for fresh air systems was proposed for regular epidemic prevention and control to ensure the normal operation of the office building and the health of indoor personnel.

Field measurements of indoor and community air quality in rural Beijing before, during, and after the COVID-19 lockdown

The coronavirus (COVID-19) lockdown in China is thought to have reduced air pollution emissions due to reduced human mobility and economic activities. Few studies have assessed the impacts of COVID-19 on community and indoor air quality in environments with diverse socioeconomic and household energy use patterns. The main goal of this study was to evaluate whether indoor and community air pollution differed before, during, and after the COVID-19 lockdown in homes with different energy use patterns. Using calibrated real-time PM2.5 sensors, we measured indoor and community air quality in 147 homes from 30 villages in Beijing over 4 months including periods before, during, and after the COVID-19 lockdown. Community pollution was higher during the lockdown (61 ± 47 μg/m3 ) compared with before (45 ± 35 μg/m3 , p < 0.001) and after (47 ± 37 μg/m3 , p < 0.001) the lockdown. However, we did not observe significantly increased indoor PM2.5 during the COVID-19 lockdown. Indoor-generated PM2.5 in homes using clean energy for heating without smokers was the lowest compared with those using solid fuel with/without smokers, implying air pollutant emissions are reduced in homes using clean energy. Indoor air quality may not have been impacted by the COVID-19 lockdown in rural settings in China and appeared to be more impacted by the household energy choice and indoor smoking than the COVID-19 lockdown. As clean energy transitions occurred in rural households in northern China, our work highlights the importance of understanding multiple possible indoor sources to interpret the impacts of interventions, intended or otherwise.

The breathing human infrastructure: Integrating air quality, traffic, and social media indicators

Outdoor air pollution is a complex system that is responsible for the deaths of millions of people annually, yet the integration of interdisciplinary data necessary to assess air quality's multiple metrics is still lacking. This case study integrates atmospheric indicators (concentrations of criteria pollutants including particulate matter and gaseous pollutants), traffic indicators (permanent traffic monitoring station data), and social indicators (community responses in Twitter archives) representing the interplay of the three critical pillars of the United Nations' Triple Bottom Line: environment, economy, and society. During the watershed moment of the COVID-19 pandemic lockdowns in Florida, urban centers demonstrated the gaps and opportunities for understanding the relationships, through correlations rather than causations, between urban air quality, traffic emissions, and public perceptions. The relationship between the perception and the traffic variables were strongly correlated, however no correlation was observed between the perception and actual air quality indicators, except for NO₂. These observations might consequently infer that traffic serves as people's proxy for air quality, regardless of actual air quality, suggesting that social media messaging around asthma may be a way to monitor traffic patterns in areas where no infrastructure currently exists or is prohibited to build. It also indicates that people are less likely to be reliable sensors to accurately measure air quality due to bias in their observations of traffic volume and/or confirmation biases in broader social discourse. Results presented herein are of significance in demonstrating the capacity for interdisciplinary studies to consider the predictive capacities of social media and air pollution, its use as both lever and indicator of public support for air quality legislation and clean-air transitions, and its ability to overcome limitations of surface monitoring stations.

Energy consumption, thermal comfort, and indoor air quality in mosques: Impact of Covid-19 measures

Restrictions have been imposed on the number of people, the duration of their stay and air conditioning operation in temples to limit the spread of the SARS-CoV-2 pandemic. This work studied how restrictions affected energy consumption, thermal comfort, and indoor air quality (IAQ) in mosques. Energy consumption data on lighting, heating and cooling before and during the pandemic were analyzed in six mosques of various sizes located in Yalova city, Turkey. The annual energy consumption for lighting was reduced during the pandemic in all mosques due to less usage, while the annual heating and cooling costs were raised in one mosque despite their restricted use. Besides, experiments were conducted to assess the effect of pandemic measures on thermal comfort and IAQ by measuring indoor temperature, relative humidity, air velocity, CO2 and PM concentrations in a typical mosque. Keeping the windows open and limiting occupancy improved the IAQ. This was evidenced by the lower average CO2 concentration during the pandemic (428 ± 40 ppm) than before the pandemic (661 ± 201 ppm). An acceptable thermal environment was achieved under pandemic measures at night during the summer period. Creating excellent conditions can be difficult without air conditioning even with open windows and prayers performed at night.

Effect of Color Temperature and Illuminance on Psychology, Physiology, and Productivity: An Experimental Study

In this study, we investigated the impact of the lighting environment on psychological perception, physiology, and productivity and then designed lighting control strategies based on the experimental results. The research was conducted in a smart lighting laboratory, and 67 subjects were tested in different illuminances and correlated color temperatures (CCTs). During the experiment, the physiological data of subjects were continuously recorded, while the psychology and productivity results were evaluated by questionnaires and working tests, respectively. The experimental results found that both illuminance and CCT could significantly influence the feeling of comfort and relaxation of the subjects. Warm CCT and higher illuminance (3000 K–590 lux) made subjects feel more comfortable. Productivity reached its maximum value with illuminance above 500 lux and equivalent melanopic lux (EML) higher than 150. The brain-wave and heart-rate changes did not have a close relationship with either illuminance or CCT, but the heart rate slightly increased in the adjustable lighting mode. Regardless of the initial value setting, the subjects preferred intermediate CCT (4200 K) and bright illumination (500 lux) after self-adjustment. Finally, we proposed three comprehensive lighting control strategies based on psychology, productivity, circadian rhythm, and energy-saving.