Indoor Environments最新文献

Due to increasing concerns related to airborne virus spread indoors, more reactive species air cleaners are being utilized in classrooms. Reactive species generated by air cleaners decompose airborne pathogens chemically, decreasing the risk of infection. Due to the high reactivity of these oxidants, reactive species may be distributed nonuniformly in indoor environments, as are viral aerosols emitted by infectors. Heterogeneous distributions of reactive species may cause spatially non-uniform removal rates of viral aerosols. However, there is little information regarding spatial distributions of either reactive species or viral aerosols in ventilated classrooms. Thus, the objective of this study was to investigate spatial distributions of reactive species and infectious aerosols and to examine how operating conditions of air cleaners affect viral aerosol removal rates. A CFD model simulated the operation of a reactive species air cleaner generating hydrogen peroxide (H₂O₂) in a mechanically ventilated 237 m³ classroom with nine occupants. The reactive species air cleaner showed a 3–20 times higher equivalent air change rate to a HEPA filter air cleaner with the same inlet and outlet flows. During the operation of reactive species air cleaners, elevated viral aerosol concentration was confined to regions near infectors. This was due to the high reactivity of reactive species, decreasing the infection probability of receptors from 3.2 % to 0.1 % with a 1-hour exposure time. As the room average concentration of reactive species increased from 15.6 to 50.4 ppb, both below the US Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) of 1000 ppb, the room average infection probability decreased from 0.3 % to 0.1 %. Due to the residence times of reactive species, the location of reactive species air cleaners affected the inactivation rate of viral aerosol, resulting in a 24 % variation of concentration difference of infectious aerosol with air cleaner locations.

As people are the ultimate arbiters of air quality in built environments, perceived air quality (PAQ) is receiving increasing attention. Odor is often designated as the main target of PAQ regulation, but due to the complex mechanism of cross-modal human perception under multi-pollutant coupling, the accuracy of odor perception evaluation and prediction in the real environment is limited. This study obtained passengers’ evaluation of their perception of cabin air quality (CAQ) and odor intensity (OI) in commercial aircraft cabins through on-board measurement of 36 flights and 878 supporting questionnaires. Although the CAQ was generally acceptable, 25 % of passengers were not satisfied, and odor complaints (OI ≥ 3) were captured on 6 flights. The odor concentration (OC) and OI in the aircraft cabin were calculated based on the olfactory threshold and the Weber-Fechner psychophysical model, and the total OC distribution in different flight phases ranged from 28.4 to 66.1. Aldehydes (especially long-chain) were most likely to be smelled directly. Limited by the two basic assumptions that VOC interaction was non-existent and that the odor intensity was only related to VOC, the accuracy of OI calculated by the existing model was about 0.4. In order to improve the accuracy of evaluation, a new data-driven model for human perception (CAQ and OI) prediction based on a knowledge-based BP neural network was proposed, and its prediction accuracy (R²: 0.81–0.87) and generalization (R²: 0.76–0.93) were verified. The new model is able to consider the interactions among individual differences, environmental factors and VOC concentrations, thus providing a method innovation for realizing people-oriented VOC control.

The size range of respiratory droplets contributing to long-range airborne transmission of infections determines the targeted intervention methods. However, the exact size range remains unknown, and the influencing parameters are also undetermined. Here, we investigated the size-resolved transport and fate of respiratory droplets in four reported venues of COVID-19 outbreaks. We utilised a transient number balance model, a set of expired droplet size distributions, existing formulas for size-resolved settling rates and filtration efficiencies, and a deposition model from the International Commission on Radiological Protection. This enabled us to obtain the size-resolved concentrations of exhaled droplets in indoor air, the size-resolved number of droplet nuclei in the inhaled air, and the number of droplets deposited throughout the respiratory tract. The newly defined airborne transmission size range of expired droplets depends on the effective dilution flow rate of the infection venue under consideration. Three criteria were proposed for determining the sizes of droplets involved in long-range airborne transmission. The airborne transmission droplets typically featured an initial diameter of 0.1–4–6 µm, with an hourly volume generation rate of 0.38–0.42 nL/h per index case in the four venues. This newly estimated volume of airborne transmission droplets provides an essential input into the viral load method for estimating the infectious quanta generation rate.

Practical significance

Our size-resolved estimation reveals that only a tiny fraction of expired infectious droplets within an airborne transmission size range survives after the removal effects of ventilation, settling, deactivation, and filtration, as well as the transient dilution effect. These droplets remain in indoor air, potentially contributing to long-range airborne transmission. The airborne transmission size range depends on the size-dependent dilution capacity of a room.

Low-cost monitors have made possible for the first time measurements of long-term (months to years) potential indoor exposures to fine particles. Indoor and outdoor measurements made over nearly 5 years (2017–2021) by the largest network of low-cost monitors in the United States (PurpleAir) are compared to the prevalence of adult smokers in 1650 Zip codes within the three West Coast states of California, Oregon, and Washington. The results show that mean potential indoor exposures above the 75th percentile of adult smoking prevalence are more than 50 % higher than those below the 25th percentile. Mean outdoor concentrations are also elevated, but by a smaller amount (∼ 20 %). Both comparisons are significant at the p < 0.001 level. The elevation of PM_2.5 concentrations with increasing smoking prevalence is evidence of environmental disparities in income, education, and other socioeconomic indices. The relatively stronger effect on indoor rather than outdoor PM_2.5 exposures highlights the importance of including indoor measurements when possible in environmental justice studies.

Research on triethylene glycol (TEG) use to disinfect airborne microorganisms have been conducted in non-realistic chamber settings. This study assesses how air temperature, humidity, HVAC settings, and filtration impact TEG's effectiveness in deactivating a common SARS-CoV-2 substitute, MS2 bacteriophage, in a simulated non-occupied office-sized chamber. The chamber was served by a dedicated HVAC system operating at 22.0, 23.5 and 25.0 °C, at 40, 55 and 70 % relative humidity, at 0, 3 and 6 air change per hour (ACH) recirculation, at 0.8, 2.5 and 5.0 ACH outdoor ventilation and at no, MERV8 and MERV14 filtration status. Airborne MS2 log₁₀ reductions in the presence of TEG increased linearly over time and we noted a higher MS2 inactivation rate with higher TEG concentration. The estimated TEG concentration needed for a one-log inactivation of the MS2 within an hour was 0.44 mg/m³. The efficacy of TEG declined with the increase in temperature from 22.0 to 25.0 °C, peaked at 55 % RH, increased with higher recirculation rates but decreased with increasing ventilation rates and higher efficiency filters. The results of our study suggest that the optimum environmental and building conditions for TEG performance is at 22.0 or 23.5 °C air temperature, 55 % relative humidity, 0.8 ACH ventilation rate and 6 ACH recirculation rate. By conducting experiments in simulated office conditions, this study closes significant knowledge gaps in TEG performance application.

Overhead gaspers with adjustable open ratios and flow directions can alter the airflow pattern in aircraft cabins and consequently influence airborne infectious diseases transmission. To achieve the optimal operations of gaspers for minimizing the passengers’ exposure risks, this study developed a Bayesian optimization method based on computational fluid dynamics (CFD). A seven-row, single-aisle, fully occupied, economy-class aircraft cabin was used for the numerical investigation. Two air distribution systems, i.e., a mixing ventilation system and a personalized displacement ventilation system, were considered. First, the open ratios of all the gaspers were optimized by the CFD-based Bayesian optimization method. The optimal operations of gaspers were determined with only 20 trials calculated by CFD using the Bayesian optimization. With the optimal open ratios of all the gaspers, the number of relatively high-risk passengers (exposure index over 0.95) was effectively reduced by at least 55% and 86% under the mixing ventilation and the personalized displacement ventilation, respectively, when compared with the results with all the gaspers turned off. Next, the optimal open ratios and flow directions of the gaspers near the index passenger were also determined by the proposed method. With the optimized operations of gaspers, the number of relatively high-risk passengers was effectively reduced by at least 50% and 67% under the mixing ventilation and the personalized displacement ventilation, respectively.

The air quality in underground railway stations (URS) poses a significant public health concern due to extremely high concentrations of particulate matter: PM₁₀ and PM_2.5. Indeed, PM sources are strong and numerous, such as train braking and tunnel effect and URS are often confined spaces with low air change rates. Despite multiple PM measurements within URS, the variability of those concentrations from stations to stations is still poorly understood. We present here a methodology for establishing a daily profile of particle mass concentrations, based on a 5-year long measurement series in a Parisian URS. This approach incorporates an extensive data cleaning process based on the identification of URS operation periods and physically inconsistent or mathematically aberrant data, together with a linear regression model. This methodology delivers three usable outcomes: a typical profile for weekdays, a typical profile for weekends, and a PM concentration Daily Amplitude Coefficient (DAC) for the considered period. The DAC is a daily metric of the pollution levels, that enables the analysis of temporal trends and facilitates the comparison with other data with other acquisition frequency. The methodology developed here in a specific URS for PM₁₀ measurements can be easily applied to different particle size fractions or to other measured parameters exhibiting a daily profile. Weekdays PM₁₀ concentrations exhibit two distinct peaks corresponding to morning and evening rush hours, with an average daytime concentration of 193 µg/m³. These peaks are delayed by ∼1 hour compared to the train traffic. Weekends show consistently lower PM levels with no observable peaks, averaging 157 µg/m³ during the day. Our analysis reveals the long-term temporal evolution of PM concentration within the URS, highlighting seasonal patterns with higher PM₁₀ concentrations observed in summer (up to 400 µg/m³) and lower values in winter (down to 250 µg/m³). This indoor seasonal evolution is not correlated with the outdoor temporal evolution, showing higher concentrations during the winter. Furthermore, our results show that the optimal period (DAC∼1) for conducting experiments to obtain reliable profiles is during the spring months (April, May, June).

In a hot-humid climate, natural ventilation is the most recommended strategy for obtaining thermal comfort indoors. The residents' behavior in opening windows and doors to promote natural ventilation is crucial for predicting thermal comfort, especially for low-income housing where energy costs can exceed household budgets. This study identifies residents’ behavior in social housing in northeast Brazil (a hot-humid climate), focusing on actions to regulate thermal comfort with natural ventilation. The methodology comprehends field research, surveys, data processing, and analysis. Interviews with 375 individuals across two social housing complexes reveal the significant role of security and cultural factors in window control behavior. The results highlight the considerable role of security and cultural factors in shaping occupant behavior concerning window control. The residents indicated that they are stimulated to open the windows and doors right after they wake up and close them at bedtime or when leaving the house. Occupancy is a significant driving factor, but the sleep period (unconscious state) plays a crucial role in determining the closure of openings, even to housing units with a 2.0 m high wall on the plot land limits and security bars on windows. This study contributes to the understanding of the complex interplay between security, cultural factors, and thermal comfort regulation, proposing valuable insights for design and policy interventions aimed at improving living conditions in similar contexts.

The effects of ceiling fans on the transmission of infectious aerosols remain poorly understood, leading to conflicting recommendations. We conducted repeated experiments in a well-controlled chamber with a typical mixing ventilation system at three different ventilation rates with and without ceiling fans. We evaluated airborne infection risks for short- and long-range transmission routes based on size-resolved tracer particles measured at various locations. We found that the mixing ventilation without fans only effectively diluted the airborne particle concentration for the long-range route but not for the short-range. By using ceiling fans to enhance air mixing, tracer particles were distributed more homogeneously throughout the room, leading to up to 77 % reduction in short-range particle exposure while a slight increase of less than 14 % in long-range exposure. Based on the dilution-based Wells-Riley model, the changes in particle concentration translated to a maximum 47 % reduction in short-range infection risk and a marginal 4 % increase for long-range transmission. Based on the dilution factors obtained from the experiments, we developed a decision-making tool that uses the ventilation rate, the number of individuals at short- and long-range, and the disease's transmissibility to decide whether the use of ceiling fans is beneficial. Deploying ceiling fans always reduces the concentration of particles in the short range and, assuming a relationship between particles and pathogens, this directly translates to a diminished short-range risk. Based on the modeling of the overall risk, the benefits of fans are highest when the room is ventilated according to code, when masking measures are in place, and when the pathogen is not highly contagious.

Exposure to indoor air pollution, particularly volatile organic compounds (VOCs), has been recognized as a risk factor in the development of respiratory and allergic diseases. VOCs are mainly emitted continuously at low concentrations from construction furniture and decoration products. Measurement campaigns carried out in new dwellings in France have shown that aldehydes predominate with a tendency to decrease formaldehyde concentrations and to increase those in hexanal. As the main route of VOCs exposure is inhalation, this project assessed the impact of a mixture of 17 VOCs representative of indoor air (in quality and quantity) on respiratory health using an in vitro approach. This original work was based on the set-up of an experimental device, combining a gas generation and dilution bench and exposure to the air-liquid interface (ALI) adapted to the reconstructed human airway epithelium model. The VOC mixture was enriched with formaldehyde or hexanal in different proportions (from 20 to 240 µg.m⁻³) to study the biological impact of these aldehydes after repeated exposures of airway epithelium. After examination of the stability of the VOC concentrations in generated mixtures and the found of the optimal operating conditions for the dynamic gas generating system, the gaseous mixtures were distributed to the epithelium using the ALI exposure system providing direct contact between the epithelium and the tested mixtures. Our device lead to reproduce real conditions of human exposure. The results showed that the inflammatory response, assessed by the production of four cytokines, varied according to the nature of the aldehyde present in the VOC mixture (formaldehyde or hexanal), its concentration, and the duration and number of exposures applied. The most original and innovative results concern those obtained with hexanal, pollutant under-researched. Our results showed that this aldehyde could pose risks to respiratory health.