Air Purifier Intervention to Remove Indoor PM2.5 in Urban China: A Cost-Effectiveness and Health Inequality Impact Study.

Using air purifiers is an intervention to reduce exposure to fine particulate matter (PM2.5) for health benefits. We performed a comprehensive simulation in urban China to estimate the cost-effectiveness of long-term use of air purifiers to remove indoor PM2.5 from indoor and ambient air pollution in five intervention scenarios (S1-S5), where the indoor PM2.5 targets were 35, 25, 15, 10, and 5 µg/m3, respectively. In scenarios S1 to S5, 5221 (95% uncertainty interval: 3886-6091), 6178 (4554-7242), 8599 (6255-10,109), 11,006 (7962-13,013), and 14,990 (10,888-17,610) thousand disability-adjusted-life-years (DALYs) can be avoided at the cost of 201 (199-204), 240 (238-243), 364 (360-369), 522 (515-530), and 921 (905-939) billion Chinese Yuan (CNY), respectively. A high disparity in per capita health benefits and costs was observed by city, which expanded with the decrease of the indoor PM2.5 target. The net benefits of using purifiers in cities varied across scenarios. Cities with a lower ratio of annual average outdoor PM2.5 concentration to gross domestic product (GDP) per capita tended to achieve higher net benefits in the scenario with a lower indoor PM2.5 target. Controlling ambient PM2.5 pollution and developing the economy can reduce the inequality in air purifier use across China.

Non-pharmaceutical interventions for COVID-19: a systematic review on environmental control measures.

The purpose of this review was to identify the effectiveness of environmental control (EC) non-pharmaceutical interventions (NPIs) in reducing transmission of SARS-CoV-2 through conducting a systematic review. EC NPIs considered in this review are room ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way-systems. Systematic searches of databases from Web of Science, Medline, EMBASE, preprint servers MedRxiv and BioRxiv were conducted in order to identify studies reported between 1 January 2020 and 1 December 2022. All articles reporting on the effectiveness of ventilation, air filtration/cleaning, room occupancy, surface disinfection, barrier devices, [Formula: see text] monitoring and one-way systems in reducing transmission of SARS-CoV-2 were retrieved and screened. In total, 13 971 articles were identified for screening. The initial title and abstract screening identified 1328 articles for full text review. Overall, 19 references provided evidence for the effectiveness of NPIs: 12 reported on ventilation, 4 on air cleaning devices, 5 on surface disinfection, 6 on room occupancy and 1 on screens/barriers. No studies were found that considered the effectiveness of [Formula: see text] monitoring or the implementation of one-way systems. Many of these studies were assessed to have critical risk of bias in at least one domain, largely due to confounding factors that could have affected the measured outcomes. As a result, there is low confidence in the findings. Evidence suggests that EC NPIs of ventilation, air cleaning devices and reduction in room-occupancy may have a role in reducing transmission in certain settings. However, the evidence was usually of low or very low quality and certainty, and hence the level of confidence ascribed to this conclusion is low. Based on the evidence found, it was not possible to draw any specific conclusions regarding the effectiveness of surface disinfection and the use of barrier devices. From these results, we further conclude that community agreed standards for well-designed epidemiological studies with low risk of bias are needed. Implementation of such standards would enable more confident assessment in the future of the effectiveness of EC NPIs in reducing transmission of SARS-CoV-2 and other pathogens in real-world settings. This article is part of the theme issue 'The effectiveness of non-pharmaceutical interventions on the COVID-19 pandemic: the evidence'.

Experimental study of the purification performance of a MopFan-based photocatalytic air cleaning system.

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2, the virus that causes the coronavirus disease (COVID)-19, is primarily transmitted through respiratory droplets which linger in enclosed spaces, often exacerbated by HVAC systems. Although research to improve HVAC handling of SARS-CoV-2 is progressing, currently installed HVAC systems cause problems because they recirculate air and use ineffective filters against virus. This paper details the process of developing a novel method of eliminating air pollutants and suspended pathogens in enclosed spaces using Photocatalytic Oxidation (PCO) technology. It has been previously employed to remove organic contaminants and compounds from air streams using the irradiation of titanium dioxide (TiO2) surfaces with ultraviolet (UV) lights causing the disintegration of organic compounds by reactions with oxygen (O) and hydroxyl radicals (OH). The outcome was two functional prototypes that demonstrate the operation of PCO-based air purification principle. These prototypes comprise a novel TiO2 coated fibre mop system, which provide very large surface area for UV irradiation. Four commercially accessible materials were used for the construction of the mop: Tampico, Brass, Coco, and Natural synthetic. Two types of UV lights were used: 365 nm (UVA) and 270 nm (UVC). A series of tests were conducted that proved the prototype's functionality and its efficiency in lowering volatile organic compounds (VOCs) and formaldehyde (HCHO). The results shown that a MopFan with rotary mop constructed with Coco fibres and utilising UVC light achieves the best VOC and HCHO purification performance. Within 2 h, this combination lowered HCHO by 50% and VOCs by 23% approximately.

Large-scale evaluation of microorganism inactivation by bipolar ionization and photocatalytic devices.

The COVID-19 pandemic has raised awareness in the spread of disease via airborne transmission. As a result, there has been increasing interest in technologies that claim to reduce concentrations of airborne pathogens in indoor environments. The efficacy of many of these emerging technologies is not fully understood, and the testing that has been done is often conducted at a small scale and not representative of applied settings. There is currently no standard test method for evaluating air treatment technologies, making it difficult to compare results across studies or technology types. Here, a consistent testing approach in an operational-scale test chamber with a mock recirculating heating, ventilation, and air conditioning (HVAC) system was used to evaluate the efficacy of bipolar ionization and photocatalytic devices against the non-enveloped bacteriophage MS2 in the air and on surfaces. Statistically significant differences between replicate sets of technology tests and control tests (without technologies active) are apparent after 1 h, ranging to a maximum of 0.88 log10 reduction for the bipolar ionization tests and 1.8 log10 reduction for the photocatalytic device tests. It should be noted that ozone concentrations were elevated above background concentrations in the test chamber during the photocatalytic device testing. No significant differences were observed between control and technology tests in terms of the amount of MS2 deposited or inactivated on surfaces during testing. A standardized, large-scale testing approach, with replicate testing and time-matched control conditions, is necessary for contextualizing laboratory efficacy results, translating them to real-world conditions, and for facilitating technology comparisons.

Health benefit/burden, PM2 .5 removal effectiveness, and power consumption based comparison of common residential air-cleaning technologies in the United States.

This modeling study compared the common air cleaners in U.S. residences based on averted disability-adjusted life years (DALYs) related to indoor PM2.5 concentration reduction and the DALYs resulted from carbon-di-oxide (CO2 ) emissions from power consumption. The technologies compared include mechanical fibrous filters, electret fibrous filters, and electronic air cleaners. For DALYs estimation, the indoor PM2.5 concentration and power consumption were first calculated and compared. These were then multiplied by the respective health damage factors. Air cleaners were compared under several indoor particle size distributions scenarios. A methodology was developed to evaluate the influence of the aging of air cleaners on the selected comparison criteria. The results suggest that the averted DALYs from indoor PM2.5 concentration reduction far supersedes the indirect DALYs associated with the operational power consumption of the air cleaners. Hence, the DALY-based ranking of the air cleaners considered was the same as that of their effectiveness to reduce indoor PM2.5 concentrations. However, the result should be taken with care as only the use-phase of air cleaners was considered. For future study, a complete life-cycle assessment is recommended. Considering aging can change the ranking of the air cleaners and is thus advised to be incorporated in further studies.

Validation of chemotherapy drug vapor containment of an air cleaning closed-system drug transfer device.

PURPOSE: The purpose of this study was to test the efficacy of ChemfortTM, an air filtration closed-system drug transfer device to prevent release of chemotherapy drug vapors and aerosols under extreme conditions. The air cleaning system is based on the adsorption of drug vapors by an activated carbon filter in the Vial Adaptor before the air is released out of the drug vial. The functionality of the carbon filter was also tested at the end of device's shelf life, and after a contact period with drug vapors for 7 days. Cyclophosphamide and 5-fluorouracil were the chemotherapy drugs tested. METHODS: The Vial Adaptor was attached to a drug vial and both were placed in a glass vessel. A needle was punctured through the vessel stopper and the Vial Adaptor septum to allow nitrogen gas to flow into the vial and to exit the vial via the air filter into the glass vessel which was connected to a cold trap. Potential contaminated surfaces in the trap system were wiped or rinsed to collect the escaped drug. Samples were analyzed using liquid chromatography tandem mass spectrometry. RESULTS: Cyclophosphamide and 5-fluorouracil were detected on most surfaces inside the trap system for all Vial Adaptors without an activated carbon filter. Contamination did not differ between the Vial Adaptors with and without membrane filter indicating no effect of the membrane filter. The results show no release of either drug for the Vial Adaptors with an activated carbon filter even after 3 years of simulated aging and 7 days of exposure to drug vapors. CONCLUSIONS: Validation of air cleaning CSTDs is important to secure vapor and aerosol containment of chemotherapy and other hazardous drugs. The presented test method has proven to be appropriate for the validation of ChemfortTM Vial Adaptors. No release of cyclophosphamide and 5- fluorouracil was found even for Vial Adaptors after 3 years of simulated aging and 7 days of exposure to drug vapors.

Unintended Consequences of Air Cleaning Chemistry.

Amplified interest in maintaining clean indoor air associated with the airborne transmission risks of SARS-CoV-2 have led to an expansion in the market for commercially available air cleaning systems. While the optimal way to mitigate indoor air pollutants or contaminants is to control (remove) the source, air cleaners are a tool for use when absolute source control is not possible. Interventions for indoor air quality management include physical removal of pollutants through ventilation or collection on filters and sorbent materials, along with chemically reactive processes that transform pollutants or seek to deactivate biological entities. This perspective intends to highlight the perhaps unintended consequences of various air cleaning approaches via indoor air chemistry. Introduction of new chemical agents or reactive processes can initiate complex chemistry that results in the release of reactive intermediates and/or byproducts into the indoor environment. Since air cleaning systems are often continuously running to maximize their effectiveness and most people spend a vast majority of their time indoors, human exposure to both primary and secondary products from air cleaners may represent significant exposure risk. This Perspective highlights the need for further study of chemically reactive air cleaning and disinfection methods before broader adoption.

Vertical macro-channel modification of a flexible adsorption board with in-situ thermal regeneration for indoor gas purification to increase effective adsorption capacity.

Adsorption has been used widely to remove indoor volatile organic compounds (VOCs). However, the large diffusion resistance inside traditional granular adsorbents renders a low VOC adsorption rate. This study proposes a modified method to achieve the rapid diffusion into the adsorbent during the initial adsorption period. A thin and flexible adsorption board with a layer of adsorbent coated on a heating film was prepared for in-situ adsorption and regeneration. Then, regular, vertical macro-channels through the adsorption board were fabricated by laser drilling to enhance mass transfer inside the board. Experimental results demonstrated that after modification, the penetration times for formaldehyde and xylene extended from 3.8 to 6.2 h, and from 62 to 99 h, respectively. The effective adsorption capacity of the modified board had increased by a multiple of two for formaldehyde and 1.8 for xylene. A mathematical model was developed and experimentally validated to evaluate the modification effect for more adsorbent-pollutant pairs. The results showed that the amplification of effective adsorption capacity was positively correlated with the Da/(K·De) parameter; this is the diffusion resistance ratio prior to and following the modification. A spectrogram of adsorbent-pollutant pairs was plotted to guide the modification. This simple macro-channel modification of the adsorption board may be used as an alternative design for adsorption applications in indoor air purification.

Engineering Solutions for Preventing Airborne Transmission in Hospitals with Resource Limitation and Demand Surge.

Among the various strategies for the prevention of airborne transmission, engineering measures are placed high in the hierarchy of control. Modern hospitals in high-income countries have mechanical systems of building ventilation also called HVAC (heating, ventilation, and air-conditioning) but installation and maintenance of such systems is a challenging and resource-intensive task. Even when the state-of-the-art technology was used to build airborne infection isolation rooms (AIIRs), recommended standards were often not met in field studies. The current coronavirus disease-2019 pandemic has highlighted the need to find cost-effective and less resource-intensive engineering solutions. Moreover, there is a need for the involvement of interdisciplinary teams to find innovative infection control solutions and doctors are frequently lacking in their understanding of building ventilation-related problems as well as their possible solutions. The current article describes building ventilation strategies (natural ventilation and hybrid ventilation) for hospitals where HVAC systems are either lacking or do not meet the recommended standards. Other measures like the use of portable air cleaning technologies and temporary negative-pressure rooms can be used as supplementary strategies in situations of demand surge. It can be easily understood that thermal comfort is compromised in buildings that are not mechanically fitted with HVAC systems, therefore the given building ventilation strategies are more helpful when climatic conditions are moderate or other measures are combined to maintain thermal comfort. HOW TO CITE THIS ARTICLE: Zia H, Singh R, Seth M, Ahmed A, Azim A. Engineering Solutions for Preventing Airborne Transmission in Hospitals with Resource Limitation and Demand Surge. Indian J Crit Care Med 2021;25(4):453-460.

Effective disinfection of airborne microbial contamination in hospital wards using a zero-valent nano-silver/TiO2 -chitosan composite.

A novel antimicrobial composite of zero-valent silver nanoparticles (AgNPs), titania (TiO2 ), and chitosan (CS) was prepared via photochemical deposition of AgNPs on a CS-TiO2 matrix (AgNPs@CS-TiO2 ). Electron microscopy showed that the AgNPs were well dispersed on the CS-TiO2 , with diameters of 6.69-8.84 nm. X-ray photoelectron spectra indicated that most of the AgNPs were reduced to metallic Ag. Fourier-transform infrared spectroscopy indicated that some AgNPs formed a chelate with CS through coordination of Ag+ with the CS amide II groups. The zones of inhibition of AgNPs@CS-TiO2 for bacteria (Escherichia coli and Staphylococcus epidermidis) and fungi (Aspergillus niger and Penicillium spinulosum) were 6.72-11.08 and 5.45-5.77 mm, respectively, and the minimum (critical) concentrations of AgNPs required to inhibit the growth of bacteria and fungi were 7.57 and 16.51 µg-Ag/mm2 , respectively. The removal efficiency of a AgNPs@TiO2 -CS bed filter for bioaerosols (η) increased with the packing depth, and the optimal filter quality (qF) occurred for packing depths of 2-4 cm (qF = 0.0285-0.103 Pa-1 ; η = 57.6%-98.2%). When AgNPs@TiO2 -CS bed filters were installed in the ventilation systems of hospital wards, up to 88% of bacteria and 97% of fungi were removed within 30 minutes. Consequently, AgNPs@TiO2 -CS has promising potentials in bioaerosol purification.

An in-situ thermally regenerated air purifier for indoor formaldehyde removal.

Formaldehyde is a common indoor pollutant that is an irritant and has been classified as carcinogen to humans. Adsorption technology is safe and stable and removes formaldehyde efficiently, but its short life span and low adsorption capacity limit its indoor application. To overcome these limitations, we propose an in-situ thermally regenerated air purifier (TRAP) which self-regenerates as needed. This purifier has four working modes: cleaning mode, regeneration mode, exhaust mode, and outdoor air in-take mode, all of which are operated by valve switching. We developed a real-scale TRAP prototype with activated carbon as adsorbent. The experimental testing showed that the regeneration ratios for formaldehyde of TRAP were greater than 90% during 5 cycles of adsorption-regeneration and that through the 5 cycles, there was no damage to the adsorption material as confirmed by scanning electron microscope (SEM) and Brunauer-Emmett-Teller (BET) tests. The total energy consumption by the prototype for purifying 1000 m3 indoor air was 0.26 kWh. This in-situ thermal-regeneration method can recover the purifier's adsorption ability through at least five cycles.

Characterization of wood dust emission from hand-held woodworking machines.

This article focuses on the prevention of exposure to wood dust when operating electrical hand-held sawing and sanding machines. A laboratory methodology was developed to measure the dust concentration around machines during operating processes. The main objective was to characterize circular saws and sanders, with the aim of classifying the different power tools tested in terms of dust emission (high dust emitter vs. low dust emitter). A test set-up was developed and is described and a measurement methodology was determined for each of the two operations studied. The robustness of the experimental results is discussed and shows good tendencies. The impact of air-flow extraction rate was assessed and the pressure loss of the system for each machine established. For the circular saws, three machines over the nine tested could be classified in the low dust emitter group. Their mean concentration values measured are between 0.64 and 0.98 mg/m3 for the low dust emitter group and from 2.55 and 4.37 mg/m3 for the high dust emitter group. From concentration measurements, a machine classification is possible-one for sanding machines and one for sawing machines-and a ratio from 1-7 is obtained when comparing the results. This classification will be helpful when a choice of high performance power tools, in terms of dust emission, must be made by professionals.

Plasma Cluster Ions Reduce the IgE-Binding Capacity of House Dust Mite Allergens under a Simulated Indoor Environmental Condition.

BACKGROUND: A high level of house dust mite (HDM) allergens in a living environment is a risk factor for both sensitization to these allergens and asthmatic attacks. We previously showed that plasma cluster ions (PCIs) impaired the IgE-binding capacity of atomized crude allergens prepared from Japanese cedar pollen and fungus under experimental conditions. OBJECTIVE: We evaluated the capacity of PCIs to impair the IgE-binding capacity of airborne HDM allergens under a simulated indoor environmental condition. METHODS: For the determination of the effects of PCIs on HDM allergens under an experimental condition, HDM extract was atomized as aqueous mist into a cylindrical experimental apparatus filled with PCIs. For the evaluation of the effects of PCIs under a simulated natural indoor environmental condition, dried HDM allergens were floated as airborne particles in an acryl cubic apparatus in the presence of PCIs. The IgE-binding capacities of the PCI- and sham-treated HDM allergens were analyzed by an ELISA. RESULTS: The IgE-binding capacity of the HDM allergens was significantly impaired after PCI treatment compared to that after sham treatment under both experimental and simulated environmental conditions. The ELISA results demonstrated that the IgE-binding capacities of HDM allergens after PCI treatment showed 68 and 74% reductions compared to those after sham treatment under the experimental and simulated environmental conditions, respectively. CONCLUSIONS: PCIs have the capacity to impair the IgE-binding capacity of airborne HDM allergens in a simulated environmental condition.

Significant OH production under surface cleaning and air cleaning conditions: Impact on indoor air quality.

We report measurements of hydroxyl (OH) and hydroperoxy (HO2 ) radicals made by laser-induced fluorescence spectroscopy in a computer classroom (i) in the absence of indoor activities (ii) during desk cleaning with a limonene-containing cleaner (iii) during operation of a commercially available "air cleaning" device. In the unmanipulated environment, the one-minute averaged OH concentration remained close to or below the limit of detection (6.5×105  molecule cm-3 ), whilst that of HO2 was 1.3×107  molecule cm-3 . These concentrations increased to ~4×106 and 4×108  molecule cm-3 , respectively during desk cleaning. During operation of the air cleaning device, OH and HO2 concentrations reached ~2×107 and ~6×108  molecule cm-3 respectively. The potential of these OH concentrations to initiate chemical processing is explored using a detailed chemical model for indoor air (the INDCM). The model can reproduce the measured OH and HO2 concentrations to within 50% and often within a few % and demonstrates that the resulting secondary chemistry varies with the cleaning activity. Whilst terpene reaction products dominate the product composition following surface cleaning, those from aromatics and other VOCs are much more important during the use of the air cleaning device.

Understanding and controlling airborne organic compounds in the indoor environment: mass transfer analysis and applications.

Mass transfer is key to understanding and controlling indoor airborne organic chemical contaminants (e.g., VVOCs, VOCs, and SVOCs). In this study, we first introduce the fundamentals of mass transfer and then present a series of representative works from the past two decades, focusing on the most recent years. These works cover: (i) predicting and controlling emissions from indoor sources, (ii) determining concentrations of indoor air pollutants, (iii) estimating dermal exposure for some indoor gas-phase SVOCs, and (iv) optimizing air-purifying approaches. The mass transfer analysis spans the micro-, meso-, and macroscales and includes normal mass transfer modeling, inverse problem solving, and dimensionless analysis. These representative works have reported some novel approaches to mass transfer. Additionally, new dimensionless parameters such as the Little number and the normalized volume of clean air being completely cleaned in a given time period were proposed to better describe the general process characteristics in emissions and control of airborne organic compounds in the indoor environment. Finally, important problems that need further study are presented, reflecting the authors' perspective on the research opportunities in this area.

Purging of working atmospheres inside freight containers.

This article focuses on prevention of possible exposure to chemical agents, when opening, entering, and stripping freight containers. The container purging process is investigated using tracer gas measurements and numerical airflow simulations. Three different container ventilation conditions are studied, namely natural, mixed mode, and forced ventilation. The tests conducted allow purging time variations to be quantified in relation to various factors such as container size, degree of filling, or type of load. Natural ventilation performance characteristics prove to be highly variable, depending on environmental conditions. Use of a mechanically supplied or extracted airflow under mixed mode and forced ventilation conditions enables purging to be significantly accelerated. Under mixed mode ventilation, extracting air from the end of the container furthest from the door ensures quicker purging than supplying fresh air to this area. Under forced ventilation, purging rate is proportional to the applied ventilation flow. Moreover, purging rate depends mainly on the location at which air is introduced: the most favourable position being above the container loading level. Many of the results obtained during this study can be generalized to other cases of purging air in a confined space by general ventilation, e.g. the significance of air inlet positioning or the advantage of generating high air velocities to maximize stirring within the volume.

A systematic review and meta-analysis of field studies of portable air cleaners: Performance, user behavior, and by-product emissions.

Indoor air quality is important for the health of building occupants, and public interest in controlling indoor airborne pathogens increased dramatically with the COVID-19 pandemic. Pollutant concentrations can be controlled locally using portable air cleaners (sometimes called air purifiers), which allow occupants to apply air cleaning technology to meet their needs in the location and times that they find appropriate. This paper provides a systematic review of scientific literature that describes field studies of the effectiveness of portable air cleaners. Over 500 papers were considered, and 148 were reviewed in detail, to extract 35 specific research results (e.g., particulate removal performance) or characteristics (e.g., type of building). These were aggregated to provide an overview of results and approaches to this type of research, and to provide meta-analyses of the results. The review includes: descriptions of the geographical location of the research; rate of publications over time; types of buildings and occupants in the field study; types of air cleaner technology being tested; pollutants being measured; resulting pollutant removal effectiveness; patterns of usage and potential barriers to usage by occupants; and the potential for by-product emissions in some air cleaner technologies. An example result is that 83 of the 148 papers measured reductions in fine particulates (PM2.5) and found a mean reduction of 49 % with standard deviation of 20 %. The aggregated results were approximately normally distributed, ranging from finding no significant reduction up to a maximum above 90 % reduction. Sixteen of the 148 papers considered gaseous pollutants, such as volatile organic compounds, nitrogen dioxide, and ozone; 36 papers considered biological pollutants, such as bacteria, viruses, pollen, fungi, etc. An important challenge, common to several studies, is that occupants run the air cleaners for shorter periods and on low airflow rate settings, because of concerns about noise, drafts, and electricity cost, which significantly reduces air cleaning effectiveness.

Experimental and Modeled Assessment of Interventions to Reduce PM2.5 in a Residence during a Wildfire Event.

Increasingly large and frequent wildfires affect air quality even indoors by emitting and dispersing fine/ultrafine particulate matter known to pose health risks to residents. With this health threat, we are working to help the building science community develop simplified tools that may be used to estimate impacts to large numbers of homes based on high-level housing characteristics. In addition to reviewing literature sources, we performed an experiment to evaluate interventions to mitigate degraded indoor air quality. We instrumented one residence for one week during an extreme wildfire event in the Pacific Northwest. Outdoor ambient concentrations of PM2.5 reached historic levels, sustained at over 200 µg/m3 for multiple days. Outdoor and indoor PM2.5 were monitored, and data regarding building characteristics, infiltration, and mechanical system operation were gathered to be consistent with the type of information commonly known for residential energy models. Two conditions were studied: a high-capture minimum efficiency rated value (MERV 13) filter integrated into a central forced air (CFA) system, and a CFA with MERV 13 filtration operating with a portable air cleaner (PAC). With intermittent CFA operation and no PAC, indoor corrected concentrations of PM2.5 reached 280 µg/m3, and indoor/outdoor (I/O) ratios reached a mean of 0.55. The measured I/O ratio was reduced to a mean of 0.22 when both intermittent CFA and the PAC were in operation. Data gathered from the test home were used in a modeling exercise to assess expected I/O ratios from both interventions. The mean modeled I/O ratio for the CFA with an MERV 13 filter was 0.48, and 0.28 when the PAC was added. The model overpredicted the MERV 13 performance and underpredicted the CFA with an MERV 13 filter plus a PAC, though both conditions were predicted within 0.15 standard deviation. The results illustrate the ways that models can be used to estimate indoor PM2.5 concentrations in residences during extreme wildfire smoke events.

Health benefits of particle filtration.

The evidence of health benefits of particle filtration in homes and commercial buildings is reviewed. Prior reviews of papers published before 2000 are summarized. The results of 16 more recent intervention studies are compiled and analyzed. Also, reviewed are four studies that modeled health benefits of using filtration to reduce indoor exposures to particles from outdoors. Prior reviews generally concluded that particle filtration is, at best, a source of small improvements in allergy and asthma health effects; however, many early studies had weak designs. A majority of recent intervention studies employed strong designs and more of these studies report statistically significant improvements in health symptoms or objective health outcomes, particularly for subjects with allergies or asthma. The percentage improvement in health outcomes is typically modest, for example, 7% to 25%. Delivery of filtered air to the breathing zone of sleeping allergic or asthmatic persons may be more consistently effective in improving health than room air filtration. Notable are two studies that report statistically significant improvements, with filtration, in markers that predict future adverse coronary events. From modeling, the largest potential benefits of indoor particle filtration may be reductions in morbidity and mortality from reducing indoor exposures to particles from outdoor air.

Fibrous Structures Produced Using the Solution Blow-Spinning Technique for Advanced Air Filtration Process.

This study proposes utilising the solution blow-spinning process (SBS) for manufacturing a biodegradable filtration structure that ensures high efficiency of particle filtration with an acceptable pressure drop. The concept of multi-layer filters was applied during the design of filters. Polylactic acid (PLA) was used to produce various layers, which may be mixed in different sequences, building structures with varying filtration properties. Changing the process parameters, one can create layers with diverse average fibre diameters and thicknesses. It enables the design and creation of optimal filtration materials prepared for aerosol particle filtration. The structures were numerically modelled using the lattice Boltzmann approach to obtain detailed production guidelines using the blow-spinning technique. The advantage of this method is the ability to blow fibres with diameters in the nanoscale, applying relatively simple and cost-effective equipment. For tested PLA solutions, i.e., 6% and 10%, the mean fibre diameter decreases as the concentration decreases. Therefore, the overall filtering efficiency decreases as the concentration of the used solution increases. The produced multi-layer filters have 96% overall filtration efficiency for particles ranging from 0.26 to 16.60 micrometres with a pressure drop of less than 160 Pa. Obtained results are auspicious and are a step in producing efficient, biodegradable air filters.