COVID-19 airborne transmission risk calculation using CO2 concentrations in a 3D office environment

The ongoing COVID-19 pandemic has caused millions of deaths worldwide along with detrimental socioeconomic consequences. Existing evidence suggests that the rate of indoor transmission is directly linked with the Indoor Air Quality (IAQ) conditions. Most of the existing methodologies for virus transmissibility risk estimation are based on the well-known Wells-Riley equation and assume well-mixed, uniform conditions;so spatiotemporal variations within the indoor space are not captured. In this work, a novel fine-grained methodology for real-time virus transmission risk estimation is developed using a 3D model of a real office room with 31 occupants. CONTAM-CFD0 software is used to compute the airflow vectors and the resulting 3D CO2 concentration map (attributed to the exhalations from the occupants). Simulation results are also provided that demonstrate the efficacy of using CO2 sensors for estimating the infection risk in real-time in the 3D office environment. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Under Pandemic: Assessment of Ventilation in Secondary Schools in The Netherlands

To investigate the sufficiency of ventilation during the COVID-19 pandemic for school children, a field study was conducted in 37 classrooms of 11 Dutch secondary schools between October 2020 and June 2021. All the classrooms were visited twice, before and after a three-month national lockdown, when different measures against COVID-19 were taken by the schools. For each visit, both CO2 concentrations and air temperature were measured during school hours, and detailed information on building/classroom characteristics, occupancy, and COVID-19 measures was collected. Results show that before the lockdown, CO2 concentrations in most classrooms exceeded the threshold levels of the Dutch Fresh Schools guidelines. The significantly lower CO2 concentrations measured after the lockdown, however, were mainly due to the decreased occupancy. Moreover, with windows and doors always being opened on purpose, the performance of different ventilation regimes could not be compared, while such behaviour may also lead to thermal discomfort for school children. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Predicting the infection probability distribution due to airborne and droplet transmission

In this study, a method was proposed to predict the infection probability distribution rather than the room-averaged value. The infection probability by airborne transmission was predicted based on the CO2 concentration. The infection probability by droplet transmission was predicted based on occupant position information. Applying the proposed method to an actual office confirmed that it could be used for quantitatively predicting the infection probability by integrating the ventilation efficiency and distance between occupants. The infection probability by airborne transmission was relatively high in a zone where the amount of outdoor air supply was relatively small. The infection probability by droplet transmission varied with the position of the occupants. The ability of the proposed method to analyze the relative effectiveness of countermeasures for airborne transmission and droplet transmission was verified in this study. © 2022 17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022. All rights reserved.

Smart Device for CO2 Measuring and Supplementing with O2 Using IOT

Globally, atmospheric carbon dioxide (CO2) concentration is rising due to rising carbon-based fuel consumption and ongoing deforestation. As carbon dioxide levels grow due to the warming trend, the atmosphere's temperature is predicted to climb. Increased fatigue, headaches, and tinnitus are just a few health issues that high CO2 concentrations in the atmosphere can cause. The electrical activities of the brain, the heart, and the lungs have all been demonstrated to change significantly after a brief exposure to 0.1 percent CO2. Continuous measurements of the atmospheric CO2 content have recently been shown to help evaluate the ventilation conditions in buildings or rooms. Additionally, it prevents the development of the severe acute respiratory syndrome coronavirus 2 (Severe acute respiratory). The coronavirus, known as a powerful acute respiratory, can make people ill. This has grown to be a significant concern in emergency medicine. © 2022 IEEE.

VENTILATION EFFECT AND THERMAL ENVIRONMENT INDUCED BY ENVIRONMENTAL CONTROL AS A MEASURE FOR COVID-19 IN ELEMENTARY SCHOOL CLASSROOMS WITH MECHANICAL VENTILATION EQUIPMENT IN TOKYO

Air temperature and CO2 concentration were measured in classrooms with ventilation system from April 2018 through March 2022. It is assumed that, under the COVID-19 circumstances, windows of the classrooms, where ventilation system was working, were basically kept open throughout a year. The average air temperature at foot level was 11℃ during winter period because of cold outdoor air infiltration. The estimated ventilation rate tended to decrease during winter period. However, the estimated ventilation rate per person more than 30 m3/h was obtained in case of half number of pupils in the classroom with Hybrid-Flexible lesson for the whole day. © 2023 Architectural Institute of Japan. All rights reserved.

CO2 concentration as an indicator of indoor ventilation performance to control airborne transmission of SARS-CoV-2.

BACKGROUND: The Wells-Riley equation has been extensively used to quantify the infection risk of airborne transmission indoors. This equation is difficult to apply to actual conditions because it requires measurement of the outdoor air supply rate, which vary with time and are difficult to quantify. The method of determining the fraction of inhaled air that has been exhaled previously by someone in a building using a CO2 concentration measurement can solve the limitations of the existing method. Using this method, the indoor CO2 concentration threshold can be determined to keep the risk of infection below certain conditions. METHODS: Based on the calculation of the rebreathed fraction, an appropriate mean indoor CO2 concentration and required air exchange rate to control SARS-CoV-2 airborne transmission was calculated. The number of indoor occupants, ventilation rate, and the deposition and inactivation rates of the virus-laden aerosols were considered. The application of the proposed indoor CO2 concentration-based infection rate control was investigated through case studies in school classrooms and restaurants. RESULTS: In a typical school classroom environment with 20-25 occupants and an exposure time of 6-8 h, the average indoor CO2 concentration should be kept below 700 ppm to control the risk of airborne infection indoors. The ASHRAE recommended ventilation rate is sufficient when wearing a mask in classrooms. For a typical restaurant with 50-100 occupants and an exposure time of 2-3 h, the average indoor CO2 concentration should be kept below about 900 ppm. Residence time in the restaurant had a significant effect on the acceptable CO2 concentration. CONCLUSION: Given the conditions of the occupancy environment, it is possible to determine an indoor CO2 concentration threshold, and keeping the CO2 concentration lower than a certain threshold could help reduce the risk of COVID-19 infection.

Carbon Dioxide Concentration Levels and Thermal Comfort in Primary School Classrooms: What Pupils and Teachers Do

The current climate emergency concerns and the COVID-19 pandemic demand urgent action to maintain healthy indoor environments in energy efficient ways. Promoting good indoor environments, in particular, increasing ventilation levels, has been a prominent strategy to mitigate the risk of COVID-19 transmission indoors. However, this strategy could be detrimental to thermal comfort, particularly during the heating season in buildings located in temperate climate zones. This paper presents research conducted in two primary schools in South Wales (UK) where the temperature, relative humidity and the carbon dioxide (CO2) concentration levels were monitored. The study monitored six classrooms and two communal spaces in the two schools during the academic year 2021/2022, the first academic year back to teaching and learning in school buildings after home-schooling and educational disruptions due to COVID-19 lockdowns. The study investigated the actions taken by teachers and pupils to balance the thermal comfort needs while minimising CO2 concentration levels. We conducted user studies to explore the comfort perceptions by pupils and teachers in relation to the thermal conditions and the freshness of air in the monitored classrooms. The paper identifies opportunities where end-users, teachers and pupils engaged with the management of the indoor environmental conditions and adopted actions to balance the requirement of reducing CO2 concentration levels while promoting thermal comfort. This research offers lessons and insights related to end-users' agency and their understanding of indoor environments and thermal experience in schools.

Evaluation of ventilation in Australian school classrooms using long-term indoor CO2 concentration measurements

School classrooms are often reported as having insufficient ventilation with elevated indoor CO2 concentrations. This paper reports on pre-pandemic field measurements of CO2 concentration levels conducted for an academic year in 10 classrooms from four primary and a secondary school in Victoria, Australia. Measured CO2 concentrations across the 10 classrooms which were operated with a mix of intermittent natural ventilation and air-conditioning for cooling or heating, on average ranged between 657 ppm and 2235 ppm during school hours with median over 1000 ppm in 70% of classrooms. All 10 classrooms in the study exceeded the Australian recommended limit of 850 ppm. Using average peak CO2 concentrations from year-long measurements, estimated ventilation rate (VR) of 4.08 Ls-1 per person show under-performing classrooms where 60% had VRs 35–40% lower than the 10-12 Ls−1 per person Australian recommendation. Estimated VR range of 1.24–2.07 Ls-1 per person using peak maximum CO2 levels were 19–30% lower than ASHRAE recommendation of 6.7 Ls-1 per person. These VRs translate to a range of air change rates on average between 0.52 and 0.88 h−1 ± 0.26–0.59, well below the 6.0 h−1 recommendation for good indoor ventilation by the World Health Organisation in the context of COVID-19 pandemic. Characterisation of ventilation and indoor air quality in current Australian classroom stock is critical for the improvement of classroom design, induction on room operating practices, understanding of the school community on the relevance of building ventilation on school performance and health, and development of appropriate ventilation and indoor air quality guidelines for schools. © 2023 The Authors

A Smart CO2-Based Ventilation Control Framework to Minimize the Infection Risk of COVID-19 In Public Buildings

This study aims to present a smart ventilation control framework to reduce the infection risk of COVID-19 in indoor spaces of public buildings. To achieve this goal, an artificial neural network (ANN) was trained based on the results from a parametric computational fluid dynamics (CFD) simulation to predict the COVID-19 infection risk according to the zone carbon dioxide (CO2) concentration and other information (e.g., zone dimension). Four sample cases were analyzed to reveal how the CO2 concentration setpoint was varied for a given risk level under different scenarios. A framework of smart ventilation control was briefly discussed based on the ANN model. This framework could automatically adjust the system outdoor airflow rate and variable air volume (VAV) terminal box supply airflow rate to meet the needs of reducing infection risk and achieving a good energy performance. © International Building Performance Simulation Association, 2022

Airborne infection risk in classrooms based on environment and occupant behavior measurement under COVID-19 epidemic

The changes of indoor environment and occupant behavior (OB) are two main causes for the gap between predicted and actual airborne infection risk. To improve the accuracy of COVID-19 airborne infection risk assessment, the environment (CO2 concentration) and OBs (occupant area per person (OA) and activity level (AL)) in three typical classrooms of a primary school in Tianjin, China was selected to conduct the on-site measurement. Based on the measured data, a modified Wells-Riley model was proposed to predict the infection risk, and a risk-controlled ventilation strategy was developed to calculate the ventilation demand. Results indicated that classrooms in the breaking time (B-T) showed a lower indoor CO2 concentration (C in), larger OA, and higher AL than in the teaching time (T-T). The variation tendency of the calculated infection risk increment in T-T was consistent with C in while in B-T was significantly affected by OA and AL, and the maximum fluctuation extent in B-T was two times of that in T-T. Moreover, to avoid the risk spreading in classrooms, a feasible solution of dynamic ventilation control based on the real-time infection risk was proposed, thus facilitating to provide a healthy and sustainable environment for students in classrooms. © 2023 Informa UK Limited, trading as Taylor & Francis Group.

The Influence of Ventilation Measures on the Airborne Risk of Infection in Schools: A Scoping Review.

OBJECTIVES: To review the risk of airborne infections in schools and evaluate the effect of intervention measures reported in field studies. BACKGROUND: Schools are part of a country's critical infrastructure. Good infection prevention measures are essential for reducing the risk of infection in schools as much as possible, since these are places where many individuals spend a great deal of time together every weekday in a small area where airborne pathogens can spread quickly. Appropriate ventilation can reduce the indoor concentration of airborne pathogens and reduce the risk of infection. METHODS: A systematic search of the literature was conducted in the databases Embase, MEDLINE, and ScienceDirect using keywords such as school, classroom, ventilation, carbon dioxide (CO2) concentration, SARS-CoV-2, and airborne transmission. The primary endpoint of the studies selected was the risk of airborne infection or CO2 concentration as a surrogate parameter. Studies were grouped according to the study type. RESULTS: We identified 30 studies that met the inclusion criteria, six of them intervention studies. When specific ventilation strategies were lacking in schools being investigated, CO2 concentrations were often above the recommended maximum values. Improving ventilation lowered the CO2 concentration, resulting in a lower risk of airborne infections. CONCLUSIONS: The ventilation in many schools is not adequate to guarantee good indoor air quality. Ventilation is an important measure for reducing the risk of airborne infections in schools. The most important effect is to reduce the time of residence of pathogens in the classrooms.

IoT platform for level detection of CO2 in closed environments

In this research seeks to implement a prevention system that measures CO2 levels in closed environments, in order to reduce the probability of contagion of SARS-COV-2. This system interacts with a microcontroller (ESP32) which will obtain the CO2 concentrations in ppm from a gas sensor (MQ-135) which in the first instance will proceed to calibrate the sensor using established formulas so that it gives exact data and can convert them to ppm. Finally, the system based on IoT technology will sfhow the concentration levels obtained in real time and thus, with already established ranges, it will indicate to the user the level of probability of contagion to which they will be exposed, making the stay in a closed environment safer. © 2022 IEEE.

Indoor air CO2 concentrations and ventilation rates in two residences in Ízmir, Turkey

Houses are the places where people spend most of their time. That is why indoor air quality at home is essential for public health. Sufficient ventilation is the factor to avoid accumulation of pollutants in indoor air, which include microorganisms, such as SARS-CoV-2. Therefore, adequate ventilation is needed to provide good indoor air quality for human health and reduce infection risk at home. There are no reports of residential ventilation rates in Turkey. In this study, CO2 concentrations were measured in two residences in Izmir, Turkey. Three experiments were conducted to determine background concentrations and the rate of natural ventilation with infiltration and opening windows. Results show that air exchange provided by infiltration is low for both case rooms, while adequate ventilation could be achieved with natural ventilation under the studied conditions. Infiltration provided air exchange and ventilation rates of 0.18 h-1 and 5.9 m3/h for Case 1 and 0.29 h-1 and 8.23 m3/h for Case 2, respectively. Air exchange and ventilation rates were increased to 2.36 h-1 and 76.9 m3/h for Case 1 and 1.2 h-1 and 34 m3/h for Case 2, respectively, by opening the windows. Although ventilation can be provided by opening the windows, the other factors that determine its rate, e.g., meteorological variables, cannot be controlled by the occupants. Consequently, people cannot ensure the good indoor air quality in bedrooms and sufficient reduction in transmission of pathogenic microorganisms;therefore, risk of spreading diseases such as COVID-19 at home. © 2022 by the Author(s).

EVALUATION ON INDOOR ENVIRONMENT AND ALTERNATIVE VENTILATION METHODS IN A SCHOOL CLASSROOM IN A COLD REGION UNDER COVID-19 PANDEMIC

COVID-19 caused a global pandemic. The possibility of aerosol transmission has been pointed out as a possible route of infection, and there are reports that conventional infection control measures are insufficient to counteract aerosol transmission. Therefore, this report presents the results of an actual survey at a high school, including measurement of CO2 concentration and a questionnaire survey, and the results of an experiment to evaluate the attenuation of particle concentration by an air cleaner based on this survey. © 2023 Architectural Institute of Japan. All rights reserved.

CO2 Levels in the Naso-Buccal Area Due to the Use of Different Face Masks in Different Ventilation Conditions

In this work, CO2 levels were estimated in the naso-buccal area due to the use of face masks. Tests were performed on a healthy volunteer subject sitting at rest and breathing regularly, who used five types of face masks in well-ventilated and poorly ventilated rooms. The ventilation conditions were determined by the natural ventilation of the room. Each of the tests lasted one hour. To estimate the CO2 level, a sensor based on the Non-dispersive Infrared (NDIR) principle was used. The results revealed that while wearing a face mask, the ventilation conditions affected the CO2 concentration levels in the naso-buccal area of the user, especially in those that offered a higher level of protection, and in those that best fit the face of the subject. A multiple comparison method (Tukey) revealed significant differences in the levels of CO2 between all the facemask tested (p < 0.0001). The CO2 levels were also compared with the exposure limits recommended by NIOSH, showing that the use of N95 for 1 h exceeded the recommended 5,000 ppm for an 8-h workday. None of the masks tested exceeded the NIOSH-recommended short-term limit in the first 15 min of use. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

Long-Term Assessment of a Set of CO2 Concentration Sensors in an In-Use Office Building.

The measurement of the CO2 concentration has a wide range of applications. Traditionally, it has been used to assess air quality, with other applications linked to the experimental assessment of occupancy patterns and air renewal rates. More recently, the worldwide dissemination of COVID-19 establishing a relationship between infection risk and the mean CO2 level has abruptly led to the measurement of the CO2 concentration in order to limit the spread of this respiratory disease in the indoor environment. Therefore, the extensive application of this measurement outside of traditional air quality assessment requires an in-depth analysis of the suitability of these sensors for such modern applications. This paper discusses the performance of an array of commercial wall-mounted CO2 sensors, focusing on their application to obtain occupancy patterns and air renovation rates. This study is supported by several long-term test campaigns conducted in an in-use office building located in south-eastern Spain. The results show a spread of 19-101 ppm, with a drift of 28 ppm over 5 years, an offset of 2-301 ppm and fluctuations up to 80 ppm in instantaneous measurements not related to concentration changes. It is proposed that values averaged over 30 min, using a suitable reference value, be used to avoid erroneous results when calibration is not feasible.

Comprehensive assessment of vertical variations in urban atmospheric CO2 concentrations by using tall tower measurement and an atmospheric transport model

In this study, we performed a comprehensive assessment of the vertical CO2 concentration in the urban atmosphere using measurements at two different heights (113 m and 420 m) in Seoul, South Korea. The difference in CO2 concentration between the two altitudes (△CO2 = CO2 at 113 m minus CO2 at 420 m) showed a significant diurnal variation, with the highest at 07:00 (19.9 ppm) and the lowest at 16:00 (3.9 ppm). When the planetary boundary layer (PBL) rose above the two sites (daytime), the CO2 concentrations at the two altitudes were highly correlated (r = 0.87) with low △CO2. In contrast, when the PBL was located between the two sites (night time), the correlation coefficient of the CO2 concentration between the two altitudes decreased by 0.55 with a high △CO2. To explain the cause of this variation in △CO2 according to PBL, we performed Weather Research and Forecasting-stochastic time-inverted Lagrangian transport (WRF-STILT) simulations. Simulations showed that CO2 measurements at two different heights were influenced by the same nearby urban areas during the daytime. However, the site above the PBL only measured the CO2 of air transported from the outside downtown area during the night time. Consequently, the observed night time △CO2 is explained by the difference in air mass between the two measurements owing to PBL variations. The night time △CO2 further implicates the local attribution of observed CO2 below the PBL by removing the effect from the remote area. Because of this unique night time characteristic of △CO2, we evaluated the changes in CO2 concentration in Seoul during the COVID-19 period. Compared to the pre-COVID-19 period, △CO2 clearly decreased from 26.5 ppm to 6.2 ppm with the implementation of social distancing, thus confirming the decreasing local influence of CO2 concentrations. Our findings highlight the potential of atmospheric CO2 monitoring at high altitudes as an observation-based method to assess the effectiveness of local carbon management. © 2022 Elsevier B.V.

Air quality in an air ventilated fitness center reopening for pilot study during COVID-19 pandemic lockdown.

During COVID-19 lockdowns less people were able to fulfill the WHO recommendations on physical activity. Also, fitness centers were associated to SARS-CoV-2 superspreader events. However, the risk of infection can be strongly reduced by outdoor air ventilation. To investigate whether a reopening of fitness centers can be justified, CO 2 concentration was measured during four days in a fitness center. Except for one room, the observed CO 2 concentrations were mainly under 800 ppm, which stands for high air quality. The strong decrease of CO 2 concentration during the 15 min evacuations following each hour of workout, speaks for the functionality of the ventilation system. In particular, the number of people present in the studio has a strong impact on the estimated CO 2 value. In a linear mixed model, an additional CO 2 concentration of 2.24 ppm (95 % confidence interval [2.04, 2.43]) was estimated for this setting with a total volume of 4065 m 3 in the fitness center and a possible air change rate per hour up to 10. This means, that for 45 visitors, 100 ppm can be added to the predicted concentration. To summarize, a combination of ventilation, restriction of the number of visitors and surveying the CO 2 concentration allowing for further restrictions in case of need, seems to be an adequate means to reduce the risk of SARS-CoV-2 infection in fitness centers.

Role of Nano-Sensors towards CO2Concentrations in an Indoor Classroom Environment to improve Occupational Health

Indoor ventilation is trivial in the current scenario of the COVID-19 pandemic in the workplace and public places. To support humans by preventing various airborne infectious diseases in the indoor environment, this work elaborates on measuring the CO2 concentrations in indoor classroom use through the sensors. It can differentiate between various changes in the environment. Due to advancements in nanotechnology and microcontroller systems, the traditional usage of sensors has moved way beyond its reach in a diverse set of fields. Electrochemical gas sensors like MQ series sensors consist of nano-materials fabricated to define characteristics like sensitivity, selectivity, etc. Using these nano-science and nano-electronics technologies, a low-cost prototype with Arduino UNO, and a few other micro-sensors (DHT11, MQ2, MQ135) to measure environmental parameters like temperature, humidity, carbon dioxide, and smoke and thus ensure a healthy workspace by continuously monitoring the readings in real-time. Classroom Environments may face various challenges in the pandemic situation where there is a massive density of occupancy as well as poor ventilation rates. The outdoor ventilation of the classroom is far more challenging than the indoor environment. The results reveal that this system can provide effective indoor monitoring and assessment for prohibiting harmful exposures and risk factors. Data analysis shows the correlation between humidity and quality of air based on CO2 concentrations. Poor ventilation can be lessened by reducing Air Conditioning systems and figuring out the pollutants present in the classroom environment benefiting the users with respiratory illness. © 2022 IEEE.

Monitoring CO2 concentration to control the infection probability due to airborne transmission in naturally ventilated university classrooms

Due to the increasing amount of time that people are spending indoors, the need to ensure adequate ventilation has become a priority. The confirmed airborne transmission of COVID-19 highlights the necessity to consider the effect of ventilation on the reduction of the infection risk. In naturally ventilated buildings, the ventilation rate is not easy to determine, and it is difficult to estimate the risk to implement preventive measures. This paper presents a method to estimate the infection probability from CO2 concentration monitoring, which was applied to university classrooms. The effects of people's activity, classroom characteristics, occupancy and protective masks were also investigated. From the method, it is possible to calculate the infection probability using CO2 dataloggers that can be adopted as 'alarm' systems to keep the infection probability below a critical value. The method will enhance healthy conditions indoors and reduce the risk of infectious diseases in the future.