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The World Health Organization has pointed out that airborne transmission via aerosol particles can be a strong vector for the spread of SARS-CoV-2. Protecting occupants from infectious diseases or harmful particulate matter (PM) in general can be challenging. While experimentally outlining the detailed flow of PM in rooms may require complex setups, computational fluid dynamics (CFD) simulations can provide insights into improving the safety of the built environment and the most effective positioning of air-purifying devices. While previous studies have typically leveraged Reynolds-averaged Navier–Stokes (RANS) approaches for predicting particle propagation, the turbulence length scales accurately captured in these simulations may not be sufficient to provide a realistic spread and the mixing of particles under the effects of forced convection. In this paper, we experimentally validate a Lattice Boltzmann very large eddy simulation (VLES) approach including particle modeling. We also demonstrate how this simulation approach can be used to improve the effectiveness of air filtration devices in realistic office environments. [ABSTRACT FROM AUTHOR]

As more and more proofs show that fine particles (diameter of 2.5~\mu \textm and below) pose more risk on human health than coarse particles, an increasing need for monitoring fine particles has emerged. A miniaturized sensor designed for measuring fine particle concentration is presented in this paper. The proposed sensor possesses a compact size of only 15 mm $\times10$ mm \times1$ mm. A virtual impactor has been integrated as a particle size selector and the design is optimized by simulation-assisted analysis. The sensor is realized by silicon microfabrication and wafer-level packaging. Testing results show that a high measurement accuracy of 2.55~\mu \text{g}/\text{m}^{3} has been achieved. [ABSTRACT FROM PUBLISHER]

PM2.5 is an important global air pollution issue. PM2.5 causes various problems on the environment and human health. Even though PM2.5 of the outdoor air is eliminated by particulate air filters, the chemicals adsorbed on the filtered PM2.5 can be outgassed and introduced into the semiconductor manufacturing facilities and processes, thus causing defects on the semiconductor chips by producing particles and haze as airborne molecular contamination. Therefore, estimating the amount of the outgassing from PM2.5 is a very important factor to control gaseous contaminants in the semiconductor industry. In this paper, the PM2.5 samples at different PM2.5 mass loadings were collected in Xi’an, China and evaluated using the soft X-ray radiolysis method for determining the relation between the outgassing and the PM2.5 mass loading. The PM2.5 samples were also analyzed by several methods for quantifying organic and elemental carbons, water soluble ions, and organic compounds in the PM2.5 samples. The outgassing measured by the soft X-ray method increased linearly with the PM2.5 mass loading, and the chemical analyses explained that the organic carbon (OC) was dominantly detected by the soft X-ray method in the current study. Moreover, the sampling location of the PM2.5 affected on the organic compounds of the PM2.5. [ABSTRACT FROM AUTHOR]

The negative impact of the presence of volatile organic compounds (VOCs) on indoor air quality has motivated researchers to develop different air treatment technologies. Although, building mechanical ventilation systems can provide a comfortable thermal indoor environment, they are not capable of removing the VOCs effectively. Thus, other components must be integrated with them to be able to carry out this function. Plasma-based air treatment techniques are a series of processes in which a high voltage discharge is used for elimination of VOCs. Development of plasma-based methods, and their capabilities for chemical gas decomposition, has motivated designers to employ these methods for indoor air purification. This paper addresses the outcomes of a critical literature review on plasma-based air cleaner technologies, thermal to non-thermal plasma and plasma catalyst, and their application for indoor environment VOCs removal. The reaction mechanism, effect of different parameters on the performance of the method, and abilities and limitations of these methods are discussed. Different types of reactors and the most common used catalysts are classified. The role of the presence of the catalyst in improving the non-thermal plasma efficiency is reviewed. Finally, the scope of the future work to enhance the performance of this method for application in sustainable buildings is discussed. [ABSTRACT FROM AUTHOR]

This study focuses on the effect of portable and large filter-based air cleaners (HEPA filters), which became popular indoors during the COVID-19 pandemic, and their suitability for classrooms (here 186 m3). The decay rates of the particle number concentration (PNC) were measured simultaneously at up to four positions in the room. It was found that the different air outlet configurations of the units have an effect on the actual PNC removal in the room when operated at the same volume flow rates. This effect of the airflow efficiency of the air cleaners (AP) in a classroom is quantified with an introduced Air Cleaning Efficiency Factor in this study to identify beneficial airflows. In this context, the effect of filter loading in long-term operation on the cleaning effect is also investigated. The emitted sound pressure levels of the APs are given special attention as this is a critical factor for use in schools, as well as power consumption. A total of six different devices were tested—two portable APs and four large APs. In order to achieve the necessary volume flow rates, three or four of the portable units were used simultaneously in one room, while only one of the large units was used per room. When used at the same air circulation rates in the room, the portable APs exhibit higher sound pressure levels compared to the large APs. At air circulation rates of 4–5 h−1, the portable APs exceeded a value of 45 dB(A). Two of the four large units reach sound pressure levels below 40 dB(A) at air circulation rates of 4–5 h−1, whereby both large units, which are positioned on the rear wall, realize a homogeneous dilution of the room air. This is achieved by an air outlet directed horizontally at a height above 2 m or diagonally towards the ceiling, which points into the room and partly to the sides. On the other hand, an air outlet directed exclusively to the sides or horizontally into the room at floor level to all sides achieves lower particle decay rates. To investigate the influence of the filter loading, three large APs were operated in a school for a period of one year (190 days with 8 h each). For the three APs, long-term operation leads to different changes in PNC reduction efficiency, ranging from −3% to −34%. It is found that not only the size of the prefilter and main filter has a significant influence, but also whether there is a prefilter bypass that negatively affects the loading level of the main filter. At the same time, it was shown that one type of AP, measuring the pressure drop across the filters and readjusting the fan, kept the circulation rate almost constant (up to −3%) over a year. [ABSTRACT FROM AUTHOR]

Summary: Insufficient quantity and quality of sleep is a public health concern that can be addressed by interventions for improving sleep outcomes. Environmental factors such as poor air quality are a potential target for intervention, particularly in light of associations between air pollution and worse sleep. The aim of this pilot study was to investigate the effects of using an air purifier on sleep outcomes and mood in 30 healthy adults. There were two conditions: (i) air purifier with a high‐efficiency particulate air filter; (ii) air purifier with a placebo filter. Participants undertook both conditions, each over 2 weeks with a 2‐week washout, following a counterbalanced, double‐blind design. Daily sleep outcomes were measured with actigraphy watches and sleep diaries, whilst daily mood was assessed with the Positive and Negative Affect Schedule. The Insomnia Severity Index, the Pittsburgh Sleep Quality Index, and symptoms of anxiety and depression were measured pre‐ and post‐. The purifier filter was associated with increased total sleep time for an average of 12 min per night, and increased total time in bed for an average of 19 min per night relative to the placebo. There were several sleep and mood outcomes for which no changes were observed, and time awake after sleep onset was higher for the purifier filter. Air quality was better during the high‐efficiency particulate air filter condition. These findings offer positive indications that environmental interventions that improve air quality can have benefits for sleep outcomes in healthy populations who are not exhibiting clinical sleep disturbances. [ABSTRACT FROM AUTHOR]

Aims: With the ongoing pandemic and increased interest in measures to improve indoor air quality, various indoor air purifiers have become very popular and are widely used. This review presents the advantages and disadvantages of various types of technologies used in air purifiers in terms of reducing microbial contamination. Methods: A literature search was performed using Web of Science, Scopus, and PubMed, as well as technical organizations dealing with indoor air-quality to identify research articles and documents within our defined scope of interest. Relevant sections: The available literature data focus mainly on the efficiency of devices based on tests conducted in laboratory conditions with test chambers, which does not reflect the real dimensions and conditions observed in residential areas. According to a wide range of articles on the topic, the actual effectiveness of air purifiers is significantly lower in real conditions than the values declared by the manufacturers in their marketing materials as well as technical specifications. Conclusions: According to current findings, using indoor air purifiers should not be the only measure to improve indoor air-quality; however, these can play a supporting role if their application is preceded by an appropriate technical and environmental analysis considering the real conditions of its use. [ABSTRACT FROM AUTHOR]

Abstract: Ultraviolet photocatalytic oxidation (UV-PCO) has been acclaimed to be a unique technology for decomposition of indoor environment VOCs while minimizing the building energy consumption. This paper addresses application of photocatalytic oxidation for indoor air treatment. Laboratory experiments were conducted in a pilot scale open test rig with an in-duct UV-PCO system. The UV-PCO reactors contain two types of flat commercially available catalyst substrates irradiated by two types of UV-lamps. UV-PCO system was challenged with aromatic: toluene, p-xylene; alcohol: 1-butanol; alkane: n-hexane, octane, and ketone: MEK, acetone. The main objectives of this study were to identify and quantify produced by-products in a large pilot scale reactor in the presence and absence of ozone. Moreover, a detailed investigation was made in order to reveal the effect of type of photocatalyst, UV-lamps as well as initial concentration on the distribution and production of by-products and removal efficiency. It was noticed that there were two common by-products including formaldehyde and acetaldehyde for all challenge compounds; moreover, some other by-products including propionaldehdye and crotonaldehyde were formed. More by-products were formed in the tested aromatic compared to the other compounds. Performance of UV-PCO system and generated by-products of challenge compounds were investigated and compared in the presence of UVC and VUV lamps, and two types of catalysts. Generally higher removal efficiency was achieved in the presence of ozone and VUV lamps compared to the UVC lamps. [Copyright &y& Elsevier]

Electrostatic precipitators (ESPs) are widely used to control air pollution. However, their applications in portable air cleaners are limited owing to ozone generation during the discharging process. In this article, we developed a compact two-stage ESP that combines corona discharging and particle collection modules. The former generates an extremely small amount of ozone using dielectric film coating, whereas the latter has a large specific surface area. A polypropylene (PP) film is coated as a dielectric material on the ground electrode of the discharging module. The corona current is reduced by the PP film, which in turn reduces the ozone generation. The efficiency of atmospheric particle collection and ozone generation were evaluated by varying the flow rates and applied voltages of the four-channel discharging and roll-type collection modules. Additionally, the specific surface area of 707 m2/m3 of the roll-type collection module minimized the size of the device by increasing its integrity. The proposed ESP with PP coating exhibited the tendency of a conventional ESP that follows the Deutsch equation. All particles of size over 1 μm were removed from the atmosphere by the proposed device at a flow rate of 194.4 L/min, which is more than three times that of human breathing. Furthermore, our experimental device removed more than 50% of the ultrafine particles of size 0.3 μm without ozone generation. Therefore, the proposed device can be potentially used in portable or wearable air-cleaning devices to aid individual healthcare. [ABSTRACT FROM AUTHOR]

The World Health Organization has pointed out that airborne transmission via aerosol particles can be a strong vector for the spread of SARS-CoV-2. Protecting occupants from infectious diseases or harmful particulate matter (PM) in general can be challenging. While experimentally outlining the detailed flow of PM in rooms may require complex setups, computational fluid dynamics (CFD) simulations can provide insights into improving the safety of the built environment and the most effective positioning of air-purifying devices. While previous studies have typically leveraged Reynolds-averaged Navier–Stokes (RANS) approaches for predicting particle propagation, the turbulence length scales accurately captured in these simulations may not be sufficient to provide a realistic spread and the mixing of particles under the effects of forced convection. In this paper, we experimentally validate a Lattice Boltzmann very large eddy simulation (VLES) approach including particle modeling. We also demonstrate how this simulation approach can be used to improve the effectiveness of air filtration devices in realistic office environments.

Purpose of Review: The goal of this review is to compress all important information and results of the research in reducing cat allergen exposure using air filtration. Fel d 1 is the major allergen responsible for IgE responses in 90 to 95% of patients with cat allergy. Recent Findings: Reduction of cat allergen in indoor air with different air filtration systems and portable devices has been demonstrated in the majority of the studies. Recently, early and late asthmatic responses were significantly reduced using portable HEPA air cleaners in an environmental exposure chamber. Summary: This review provides a comprehensive overview of the current state of airborne Fel d 1 air filtration targeting the most efficient devices in cat allergen reduction. Novel emerging HEPA filters are targeting reduction of cat indoor asthma trigger so patient can might benefit from efficient solution. [ABSTRACT FROM AUTHOR]

Background: Air cleaners have been promoted for respiratory allergic disease prevention, but there is no clear clinical proof of their efficacy in allergic asthma. Objective: To examine the efficacy of a new air cleaner on early and late asthmatic responses in cat‐allergic patients. Methods: This randomized, cross‐over, double‐blind placebo‐controlled study enrolled 24 cat‐asthmatic patients with GINA 1 asthma. At baseline, participants were exposed to 40 ng/m3 of airborne cat allergen for a maximum of 2 hours in ALYATEC® environmental exposure chamber (EEC). All participants were subsequently randomized into two groups that were exposed to cat allergen, either with active then placebo air cleaners or with placebo then active air cleaners with a 3‐week interval in the EEC. This study was registered under number (NCT03928561). Results: Fewer patients experienced an EAR with active air cleaners (seven patients; 29.17%) than placebo (21 patients; 87.50%). The response incidence was lower with active than with placebo air cleaners. A Cox model demonstrated a significant treatment effect (hazard ratio, 0.10; P =.002). Active air cleaners also prevented late asthmatic response: four patients (16.67%) had a late asthmatic response with active air cleaners compared to 11 patients (45.83%) with placebo (Prescott test P =.002). Active air cleaners also decreased the maximal severity of bronchial response (FEV1 decrease of 17.24% with active vs 25.62% with placebo air cleaners; P =.001). Conclusions: Our present results demonstrated that Intense Pure Air XL® air cleaners significantly prevented early and late asthmatic responses among cat‐allergic asthmatics during cat allergen exposure in the ALYATEC® EEC. [ABSTRACT FROM AUTHOR]

In recent years, the deterioration of indoor air quality (IAQ) became a big concern. Because indoors is the place where we spend most of our life, an IAQ is an important factor to be considered for comfortable and healthy living. In this study, we evaluated the products and decomposition process of hexadecane in small and large capacity spaces by using microplasma electrode. In the case of hexadecane removal, both small and large capacity microplasma process could reduce hexadecane by 83% and 89%, respectively. In the process, we found various hydrocarbons such as 1-hexene (C6H12), 1-heptene (C7H14), and 1-octene (C8H 16) as intermediate products. CO2 and N2O were also confirmed as final products of the microplasma treatment process. [ABSTRACT FROM PUBLISHER]

Atmospheric microplasma has the potential to be one of the technologies used to purify indoor air. For example, plasma is used for pollutant decomposition or sterilization. In this study, we examined the removal of hexadecane by using microplasma. Hexadecane is contained in diesel oil and it is discharged to the air as exhaust gas. A decrease in the concentration of hexadecane from 3000 to 105 ppm was observed after 120 min of plasma processing. The removal energy efficiency of hexadecane was evaluated to 19.8 μg/W·h. Several by-products were obtained with the plasma process and were analyzed by detector tubes, Fourier transform infrared spectroscopy, and gas chromatograph–mass spectrometer. According to the analysis of the products, hexadecane was decomposed to alkane or alkene, which contains less carbon number 16, and finally, it was decomposed to CO. It became apparent that plasma can cut carbon bonds. [ABSTRACT FROM PUBLISHER]

We developed a novel electrostatic air purifier using a carbon fiber brush charger combined with a metallic collection rod and an activated carbon fiber (ACF) sheet to improve the indoor air quality of passenger vehicles. The ACF sheet was used to apply electrostatic forces to move charged particles toward a collection rod and simultaneously adsorb gas. The cylindrical air purifier (diameter: 100 mm, length: 190 mm) was composed of a conductive brush charger and an electrostatic collection rod for particle removal, as well as an ACF filter for gas removal. The flow rate of the device was approximately 209–360 L/min. The novel purifier was tested in a 1-m3 chamber with particles 0.3 μm in diameter and three gases: ammonia, acetic acid, and acetaldehyde. The gas cleaning performance of the purifier was compared with that of a commercial purifier with a high-efficiency particulate air (HEPA) filter, activated carbon pellets, and alumina balls. The clean air delivery rate (CADR) of the novel electrostatic air cleaner was 0.219 m3/min, 35% higher than that of the HEPA filter. The CADRs of the ESP air cleaner for the test gases were 0.25, 0.19, and 0.19 m3/min, respectively, indicating that the novel ESP air cleaner reduced the gases 308%, 204%, and 327%, respectively, faster than the commercial purifier. [ABSTRACT FROM PUBLISHER]

Portable photocatalytic air cleaners were investigated in 24 and 48 m emission test chambers with regard to efficiency and by-product generation. For this purpose, formaldehyde, decane, 1,2-dichlorobenzene, toluene, α-pinene and heptanal were doped at sub-ppm concentration levels into the chambers individually and in mixtures. By way of specified test protocols, efficiencies could be distinguished but were strongly dependant on the choice of test compounds, especially on whether single or multi compound dosing was used, and on long-term effects. Initial clean air delivery rates (CADRs) up to 137 m/h were measured. Typical by-products were found in significant concentrations. The main ones were formaldehyde up to 50 ppb (62 μg/m) and acetone up to 80 ppb (190 μg/m). Other aldehydes were also found, but at smaller levels. The detection of chloroacetone, a strong irritating compound, at concentrations up to 15 ppb (57 μg/m) strengthens the importance of such investigations especially in cases were chloro-organic compounds are involved. [ABSTRACT FROM AUTHOR]

In the branches of engineering that deal with relatively large volumes of gases, it is often desirable to monitor small variations in pressure that may develop within such volumes. For example, it is important to balance the airflow in a HVAC system, detect the degree of clogging of an air filter, and monitor human movement in an enclosed space for security and "smart home" applications. [ABSTRACT FROM PUBLISHER]

Health risks of fine particle air pollution (PM2.5) are an important public health concern that has the potential to be mitigated in part by interventions such as air cleaning devices that reduce personal exposure to ambient PM2.5. To characterize exposure to ambient PM2.5 indoors as a function of residential air cleaners, a multi-zone indoor air quality model was used to integrate spatially resolved data on housing, meteorology, and ambient PM2.5, with performance testing of residential air cleaners to estimate short-term and annual average PM2.5 of outdoor origin inside residences of three metropolitan areas. The associated public health impacts of reduced ambient PM2.5 exposure were estimated using a standard health impact assessment methodology. Estimated indoor levels of ambient PM2.5 varied substantially among ventilation and air cleaning configurations. The median 24-h average indoor–outdoor ratio of ambient PM2.5 was 0.57 for homes with natural ventilation, 0.35 for homes with central air conditioning (AC) with conventional filtration, and 0.1 for homes with central AC with high efficiency in-duct air cleaner. Median modeled 24-h average indoor concentrations of PM2.5 of outdoor origin for those three configurations were 8.4, 5.3, and 1.5 μg/m3, respectively. The potential public health benefits of reduced exposure to ambient PM2.5 afforded by air cleaning systems were substantial. If the entire population of single-family homes with central AC in the modeling domain converted from conventional filtration to high-efficiency in-duct air cleaning, the change in ambient PM2.5 exposure is estimated to result in an annual reduction of 700 premature deaths, 940 hospital and emergency room visits, and 130,000 asthma attacks in these metropolitan areas. In addition to controlling emissions from sources, high-efficiency whole-house air cleaner are expected to reduce exposure to particles of outdoor origin and are projected to be an effective means of managing public health impacts of ambient particle pollution. [ABSTRACT FROM AUTHOR]

Background: Exposure and sensitization to pet allergens are associated with allergic asthma in children. Conflicting data have emerged regarding the potential benefit of air cleaners with respect to a reduction of indoor pet allergens and bronchial hyperresponsiveness (BHR). Methods: In a randomized controlled trial 36 asthmatic children with sensitization to cat and/or dog and significant exposure to cat and/or dog allergen (Fel d 1 and/or Can f 1 >500 ng/g of carpet dust) were included in order to study the effect of high-efficiency particulate arresting (HEPA) air cleaners placed in the living room and bedroom compared with the effect of sham air cleaners. Patients were allocated to two groups: group 1 exposed to active filters and group 2 exposed to sham filters. At month 0, after 6 months and after 12 months, pulmonary function testing and cold air challenge were performed, serum eosinophil cationic protein (ECP) and specific IgE to seven aeroallergens were determined, and carpet dust samples and filters were collected. Major pet allergen concentrations (Fel d 1, Can f 1) were determined in filters and bulk dust samples. Results: Thirty patients completed the study. After 6 and 12 months, there was no significant change in delta FEV1 after cold air challenge, or in the use of medication and serum ECP levels. However, there was a trend in the active group towards an improvement of bronchial hyperresponsiveness, whereas the sham filter group showed a deterioration of BHR. Conclusion: Although HEPA air cleaners retained airborne pet allergens, no effect on disease activity or allergen concentrations in bulk dust samples was observed in this study. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]