Removal Of Airborne Particles Research Articles

磁気フィルタによる空気中微粒子の除去 : 第5報-直交型網目状磁気フィルタの除じん性能

磁気フィルタによる空気中微粒子の除去 : 第5報-直交型網目状磁気フィルタの除じん性能

Recognizing Dew as an Indicator and an Improver of Near-Surface Air Quality

The relationship between dew and airborne particles is important in urban ecosystems, but the capability of dew to remove airborne particles remains unclear. During 2015 in Changchun, China, 74 dew and particle samples were collected simultaneously to investigate their chemical characteristics under normal, fog, and haze conditions. Analyses included measuring total dissolved solids, total suspended particulates, PM2.5 and PM10 concentrations, major cations (NH4+, Na+, K+, Ca2+, and Mg2+), major anions (F−, Cl−, SO42-, and NO3-), and organic and elemental carbon. Results showed that air quality deteriorated during haze but improved in fog. The particle size distributions, major cations, and carbonaceous species documented in the dew and airborne particles demonstrated consistent synchronous patterns with values descending in the order haze > normal > fog conditions. We found that dew is a good indicator of near-surface air quality. Specifically, its water-soluble ions and carbonaceous species could be used to distinguish emission sources and to identify the presence of secondary organic carbon. Dew is more effective at removing airborne particles in normal weather than in haze or fog conditions; PM2.5 removal rates were 21.5%, 15.2%, and 13.7% on normal, foggy, and hazy days, respectively. Dew condensation processes reduce concentrations of gaseous and particulate pollutants in the near-surface layer.

Capture of Sub-500 nm Particles Using Residential Electret HVAC Filter Media-Experiments and Modeling

ABSTRACTElectret HVAC filter are widely used to remove airborne particles in residential or commercial indoor environments. Based on the International Commission on Radiological Protection (ICRP) deposition model, sub-500 nm particles have enhanced depositions in the tracheobronchial region and the alveolar region than particles larger than 500 nm. In this study, filtration efficiencies of five residential electret HVAC filters against monodisperse silver (Ag) and potassium chloride (KCl) particles with 3–500 nm diameters at face velocities ranging 0.05–1.5 m s–1 were investigated. For further understanding the effect of fiber charges on particle collections, electret media were discharged and the efficiencies acquired from pure mechanical mechanisms were compared with that of electret media. The figure of merit (FOM) of the five electret filter media was also investigated to further understand the effect of charge density on filtration performance. A theoretical model without parametric fittings used in literature was adopted and further modified by considering the polarization forces for charged particles. The modified model predicted the particle penetrations very well at low face velocities for all tested media and also well at high face velocities for the media with low charges. The discrepancy occurred for the media with high charges at higher face velocities was due to the nonuniform particle concentration distribution in the media layers. The validated model is able to be applied to improve the design for electret media for nanoparticle removal.

Evaluation of an electrostatic particle ionization technology for decreasing airborne pathogens in pigs.

Influenza A virus (IAV), porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV) and Staphylococcus aureus are important swine pathogens capable of being transmitted via aerosols. The electrostatic particle ionization system (EPI) consists of a conductive line that emits negative ions that charge particles electrically resulting in the settling of airborne particles onto surfaces and potentially decreasing the risk of pathogen dissemination. The objectives of this study were to determine the effect of the EPI system on the quantity and viability of IAV, PRRSV, PEDV and S. aureus in experimentally generated aerosols and in aerosols generated by infected animals. Efficiency at removing airborne particles was evaluated as a function of particle size (ranging from 0.4 to 10 µm), distance from the source of ions (1, 2 and 3 m) and relative air humidity (RH 30 vs. 70 %). Aerosols were sampled with the EPI system “off” and “on.” Removal efficiency was significantly greater for all pathogens when the EPI line was the closest to the source of aerosols. There was a greater reduction for larger particles ranging between 3.3 and 9 µm, which varied by pathogen. Overall airborne pathogen reduction ranged between 0.5 and 1.9 logs. Viable pathogens were detected with the EPI system “on,” but there was a trend to reducing the quantity of viable PRRSV and IAV. There was not a significant effect on the pathogens removal efficiency based on the RH conditions tested. In summary, distance to the source of ions, type of pathogen and particle size influenced the removal efficiency of the EPI system. The reduction in infectious agents in the air by the EPI technology could potentially decrease the microbial exposure for pigs and people in confinement livestock facilities.Electronic supplementary materialThe online version of this article (doi:10.1007/s10453-015-9413-3) contains supplementary material, which is available to authorized users.

Experimental Study on Charge Decay of Electret Filter Due to Organic Solvent Exposure

The electret filter is a potential component to remove airborne particles due to its high collection efficiency and low pressure drop. However, its filtration performance is gradually decreased by exposure to organic solvents, which limits the application of electret filters. The effect of ethanol exposure on the filtration performance of polypropylene electret filters was investigated experimentally to clarify the charge decay phenomenon in this study. Experimental results revealed that filter performance is strongly dependent upon the challenged mass and existing state of an ethanol solvent. The filter performance was drastically degraded by exposure to ethanol droplets generated from a solution with ethanol concentrations above 30%; however, it was maintained during exposure to ethanol vapors. This tendency was also seen in the surface potentials of the exposed filter media. In addition, we found that the critical challenging amount of ethanol droplets was in the vicinity of 0.045 g/cm2 to neutralize a...

Accumulation of particles on the surface of leaves during leaf expansion

Plants can effectively remove airborne particles from ambient air and consequently improve air quality and human health. The accumulation of particles on the leaf surfaces of three plant species with different epicuticular wax ultrastructures, such as thin films, platelets and tubules, was investigated during leaf expansion in Beijing under extremely high particulate matter (PM) concentration. The accumulation of particles on the leaf surfaces after bud break rapidly reached a high amount within 4–7days. Rainfall occasionally resulted in a considerable increase in the accumulation of particles on the leaf surfaces at a high PM concentration, which resulted from the wet deposition of PM, and balanced the amount of PM on the leaf surfaces over a longer period. The equilibrium value of the particle cover area on the adaxial leaf surface of the three test species in this study was 10%–50% compared with 3%–35% on the abaxial leaf surface. The epicuticular wax ultrastructures contributed significantly to the PM adsorption of the leaves. The capability of these ultrastructures to capture PM decreased in the following order: thin films, platelets and tubules. The ridges (at a scale of 1–2μm) on the leaf surfaces were more efficient at accumulating PM, particularly PM2.5, compared with the roughness (P–V distance) at a 5–20-μm scale.

Numerical and experimental analysis of airborne particles control in an operating theater

The design of a ventilation system for operating theaters (OT) is aimed to reduce the patient infection risk while maintaining adequate comfort and productivity for the surgical staff. Nowadays, Computational Fluid Dynamics (CFD) represents an important tool to simulate the airflow pattern in an operating theater and its ability to remove airborne particles. The CFD advantages, compared to experimental campaigns, consist in the ability to test different configurations, in the ease of implementation and in time and money savings. The aim of this work is to numerically and experimentally investigate an OT with a layout according to the Standard DIN 1946-4. Moreover the effectiveness of a differential airflow diffusion system on reducing the particle concentration above the operating table is analyzed. The supply air comes from a ceiling filter system composed of 23 H14 filters, which assures an unidirectional flow with differential air velocities over the protected area. In order to experimentally evaluate the performance and the protection grade SG, according to DIN 1946-4, and to validate the numerical results, a measuring campaign has been carried out within a laboratory setup of an OT. Two different scenarios have been adopted to evaluate the protection level against the entry of external and internal contaminant loads into the protected area. For both cases, the simulated and measured particle concentration in the protected area agree well, and the differential air flow diffusion system is able to maintain the desired protective effect (SG) against contamination load in both the design and the off-design conditions.

Variation of clean air delivery rate and effective air cleaning ratio of room air cleaning devices

Air cleaners have been normally used to remove airborne particles from indoor air, and these devices are normally rated according to their clean air delivery rate (CADR), which is a measure of the delivery of contaminant-free air. This study evaluated and compared the performance of room air cleaning devices in removing submicron-sized particles. Most of the CADRs that were experimentally obtained were lower than that stated by the manufacturer. The difference between the experimental measurements and the device specifications gradually increases as the CADR increased. For the same air cleaning device, the experimental CADR decreased as the size of the test chamber increased. The effective air cleaning ratio (EACR) was newly defined to provide an accurate measure of the CADR. The EACR is the ratio of the real CADR to the stated CADR. The experiments and simulations revealed that the EACR of the air cleaning devices was in the range of 0.70–0.83. The ECAR is little changed with respect to the size of the test chamber and the flow rate of the air cleaning devices, unlike the experimental CADR. The real CADR is affected by the filtration efficiency, the flow rate, and the design of the air cleaning device as well as the size of the test particles. The real CADR decreases as the particle size increases. Therefore, the recommended CADR of air cleaning devices for use in facilities with sensitive populations or hospitals must be higher than that for general purpose use.

Soft-X-Ray-Enhanced Electrostatic Precipitation for Protection against Inhalable Allergens, Ultrafine Particles, and Microbial Infections

Protection of the human lung from infectious agents, allergens, and ultrafine particles is difficult with current technologies. High-efficiency particulate air (HEPA) filters remove airborne particles of >0.3 μm with 99.97% efficiency, but they are expensive to maintain. Electrostatic precipitation has been used as an inexpensive approach to remove large particles from airflows, but it has a collection efficiency minimum in the submicrometer size range, allowing for a penetration window for some allergens and ultrafine particles. Incorporating soft X-ray irradiation as an in situ component of the electrostatic precipitation process greatly improves capture efficiency of ultrafine particles. Here we demonstrate the removal and inactivation capabilities of soft-X-ray-enhanced electrostatic precipitation technology targeting infectious agents (Bacillus anthracis, Mycobacterium bovis BCG, and poxviruses), allergens, and ultrafine particles. Incorporation of in situ soft X-ray irradiation at low-intensity corona conditions resulted in (i) 2-fold to 9-fold increase in capture efficiency of 200- to 600-nm particles and (ii) a considerable delay in the mean day of death as well as lower overall mortality rates in ectromelia virus (ECTV) cohorts. At the high-intensity corona conditions, nearly complete protection from viral and bacterial respiratory infection was afforded to the murine models for all biological agents tested. When optimized for combined efficient particle removal with limited ozone production, this technology could be incorporated into stand-alone indoor air cleaners or scaled for installation in aircraft cabin, office, and residential heating, ventilating, and air-conditioning (HVAC) systems.

Removal of exhaled particles by ventilation and deposition in a multibed airborne infection isolation room

Removal of airborne particles in airborne infection isolation rooms is important for infection control of airborne diseases. Previous studies showed that the downward ventilation recommended by Centers for Disease Control and Prevention (CDC) could not produce the expected 'laminar' flow for pushing down respiratory gaseous contaminants and removing them via floor-level exhausts. Instead, upper-level exhausts were more efficient in removing gaseous contaminants because of upward body plumes. The conventional wisdom in the current CDC-recommended design is that floor-level exhausts may efficiently remove large droplets/particles, but such a hypothesis has not been proven. We investigated the fate of respiratory particles in a full-scale six-bed isolation room with exhausts at different locations by both experimental and computational studies. Breathing thermal manikins were used to simulate patients, and both gaseous and large particles were used to simulate the expelled fine droplet nuclei and large droplets. Gaseous and fine particles were found to be removed more efficiently by ceiling-level exhausts than by floor-level exhausts. Large particles were mainly removed by deposition rather than by ventilation. Our results show that the existing isolation room ventilation design is not effective in removing both fine and large respiratory particles. An improved ventilation design is hence recommended. Our findings of the relatively poor performance of fine-particle removal by the existing CDC design of isolation room ventilation suggests a need for improvement, and the findings of the removal of large particles by deposition, not by ventilation, suggest that floor-level exhausts are unnecessary, and that regular surface cleaning and disinfection is necessary, thus providing evidence for maintaining isolation room surface hygiene.

Removal of Biological Aerosols by Oil Coated Filters

AbstractAn elevated risk associated with exposure to bioaerosols calls for the development and implementation of new, efficient and cost effective methods of airborne biological particle control. While filtration remains the most efficient method of removal of airborne particles, some issues related to possible re‐entrainment of captured particles from the rear face of the filter back into the air carrier have to be addressed. Obviously, viable biological particles blown off from the filter surface could still cause substantial damage to human and animal health and contaminate the ambient air environment. A new technology utilizing coating of filter fibres by biologically active tea tree oil (TTO) is considered in this paper. It was found that precoating of filter fibres with TTO and following usage of such filters for bioaerosol control could provide significant benefits in terms of rapidly inactivating captured microorganisms and, minimizing the number of live/viable particles possibly blown off from the filter by the air. Three bacterial strains with a range of biological stress sensitivity were used in this research. It was found that 99% of stress sensitive Escherichia coli and Pseudomons fluorescens are inactivated on the surface of the TTO coated filter within 8 and 2 min of exposure, respectively. A robust strain of Bacillus subtilis demonstrated inactivation in the order of one logarithm per 30 min of process operation. These results look very promising for the implementation of this new technology for the control of air quality in domestic and industrial applications.

Laboratory and On-Road Evaluations of Cabin Air Filters Using Number and Surface Area Concentration Monitors

An automotive cabin air filter's effectiveness for removing airborne particles was determined both in a laboratory wind tunnel and in vehicle on-road tests. The most penetrating particle size for the test filter was approximately 350 nm, where the filtration efficiency was 22.9 and 17.4% at medium and high fan speeds, respectively. The filtration efficiency increased for smaller particles and was 43.9% for 100 nm and 72.0% for 20 nm particles at a medium fan speed. We determined the reduction in passenger exposure to particles while driving in freeway traffic caused by a vehicle ventilation system with a cabin air filter installed. Both particle number and surface area concentration measurements were made inside the cabin and in the surrounding air. At medium fan speed, the number and surface area concentration-based exposure reductions were 65.6 +/- 6.0% and 60.6 +/- 9.4%, respectively. To distinguish the exposure reduction contribution from the filter alone and the remainder of the ventilation system, we also performed tests with and without the filter in place using the surface area monitors. The ventilation system operating in the recirculation mode with the cabin air filter installed provided the maximum protection, reducing the cabin particle concentration exponentially over time and usually taking only 3 min to reach 10 microm2/cm3 (a typical office air condition) under medium fan speed.

Effectiveness of Electrostatically Charged Water Spray in Reducing Dust Concentration in Enclosed Spaces

This research investigated the potential of electrostatically charged water spray in reducing dust concentration in airspaces under controlled laboratory conditions. Test particles (i.e., corn starch and NaHCO3) were each aerosolized into in an enclosed experimental chamber (L = 3.6 m, W = 2.4 m, H = 2.4 m). Charged water droplets were then sprayed into the chamber. An Aerodynamic Particle SizerTM (APS) spectrometer was used to measure the particle concentration and size distribution. In addition, a tapered element oscillating microbalance (TEOM) was used to measure the mass concentration. From the APS and TEOM data, the particle removal efficiency of the charged water spray was determined. The particle removal efficiency of the charged water spray was significantly greater than that for the uncharged water spray. Results also showed that longer charged spray durations (i.e., 4 and 6 min) were more effective than the shorter spray duration (i.e., 2 min) in removing airborne particles. In addition, the polarity of the charged water droplets (negative vs. positive) did not significantly affect the removal efficiency of the charged water spray.

Effect of wall surface materials on deposition of particles with the aid of negative air ions

This work studied how wall surface materials influence the removal of airborne particles with negative air ions (NAIs) in indoor environments. Five wall surface materials—stainless steel, wood, PVC (polyvinyl chloride), wallpaper and cement paint—were applied to the inner surface of a test chamber. Two monodispersed solid NaCl particle sizes, 300 and 30 nm, were tested. The NAIs in the chamber were generated by negatively electric discharge in the range 3000–5000 ions cm - 3 . Experiments on the natural decay and application of NAIs were conducted at an air exchange rate of 1 h - 1 . The decay coefficient, the removal efficiency, the time to halve the concentration ( T 50 ) and the effective cleaning rate (ECR) were taken into account. The experimental data revealed that NAIs enhanced the removal of both 300 and 30 nm particles for each wall surface material. The decay coefficients of the NAI applications ( k a ) were 2.9–7.4 and 2.5–4.0 times higher than those of natural decay ( k n ) for 300 and 30 nm particles, respectively. However, the effect of the wall surfaces on the removal of particles was observed in both natural decay and NAI application experiments. The order of natural decay for 300 and 30 nm particles under different wall surfaces was cement paint > PVC ≅ wallpaper ≅ wood > stainless steel, as perhaps determined by the roughness of the wall materials. The overall removal efficiencies of 300 and 30 nm particles during 30 min of NAI emission were over 60% and 80%, respectively, in the chamber with wood and PVC wall surfaces. The half concentration times ( T 50 ) of NAI applications for various wall surfaces were less than 20 min, except for stainless steel and cement paint walls. The ECR demonstrated that the net effects of the NAIs for 300 nm particles followed the order wood (34.6 Lpm) > PVC (33.3 Lpm) > wallpaper (27.0 Lpm) > stainless steel (16.6 Lpm) > cement paint (14.8 Lpm). The ECR for 30 nm particles followed the order wood (41.4 Lpm) > PVC (30.4 Lpm) ≅ cement paint (30.3 Lpm) > wallpaper (27.7 Lpm) > stainless steel (20.1 Lpm). The NAI could remove particles from the wood and PVC wall surfaces substantially more effectively than from other wall materials. The various electrical characteristics and roughness of the wall materials may have been responsible for the associated of the various ECRs with the various wall surface materials.

Computerized control of the procedure for detecting and removing airborne particles in operating rooms.

Surgical-site infections are still a major problem in modern medicine. Normal skin fora of patients or healthcare workers causes more than half of all infections following clean surgery, but the importance of airborne particles in this setting remains controversial. The use of ultraclean air in operating rooms has been shown to reduce infection rates significantly. High efficiency particlulate air (HEPA) filters are used in some modern operating rooms. Although the uses of HEPA filters, the air quality should be controlled by another device to make safe the air in operating rooms and intensive care units. In this study, a computerized system was established to control the cleanliness of the air by measuring the presence of airborne particles of varying sizes and numbers in operating rooms. When the maximum values are exceeded, the system warns the authorized people by phone, sound, or displays.

Removal of domestic airborne dust particles by naturally charged liquid sprays

Exposure to indoor particulate pollutants and allergens has been associated with recent increases in the prevalence of allergic diseases like asthma. Reducing exposure to these particles can play an important role in prevention and abatement of asthma symptoms. A spray of fine water droplets is a well-known method for removing airborne particles. This paper presents evidence to show that the fine sprays produced by domestic pressure-pack dispensers deplete the concentration of dust particles, and when these sprays are charged, particle depletion is significantly improved. Using an air particle counter to quantify particle concentrations, comparisons were made of the rate of particle depletion by liquid aerosols with the rate at which settling occurred through natural processes alone. A standard spray from a pressure-pack dispenser with a charge-to-mass ratio ( q/ m) of 14 μC/kg was compared with a naturally charging equivalent with a q/ m of 140 μC/kg. The standard aerosol removed up to 62% of dust particles, while the charged equivalent removed up to 78% within 90 s of spraying. The sprays differed slightly in their droplet size distributions, the charged spray comprising droplets with a volume median diameter (VMD) of 42 μm and the standard spray having a VMD of 35 μm. Comparing uncharged sprays we also measured a trend for small droplets (VMD=26 μm) to deplete particle concentration more efficiently than a spray with larger droplets (VMD=36 μm). Thus, despite the charged spray having slightly larger droplets, the electrostatic charge resulted in more effective airborne particle removal than uncharged sprays. The use of domestic pressure-pack sprays, of the type used as room fragrance sprays, offers an inexpensive and convenient method of removing airborne dust and associated allergens in the home. This would be of particular benefit following domestic activities that entrain airborne dust.

Collection of Airborne Microorganisms into Liquid by Bubbling through Porous Medium

A new method for the removal of airborne particles by air bubbling through fibrous filters immersed into a liquid has recently been developed (Agranovski et al. 1999) and shown to be very efficient for cleaning air environments with ultra-fine aerosol particles. The principal objective of the present study was to evaluate the new bubbling technique for the collection of airborne bacteria into a liquid for subsequent physical and microbiological analysis. It was found that the technique is capable of achieving a physical collection efficiency of 98.5% or higher for particles larger than 0.3 w m in aerodynamic diameter. The physical collection efficiency of the prototype bubbler remained at that high level for 8 h of continuous operation with negligible variation of the pressure drop across the device. Evaporation of the collection fluid did not exceed 20% during 8 h, and the reaerosolization effect on the physical collection efficiency of the bubbler prototype was <8%. The recovery rate of gram-negative Ps...

Avoidance of allergens and air pollutants in respiratory allergy

Avoidance of allergens and air pollutants in respiratory allergy

Application of virtual reality in hospital facilities design

The airborne particles present in certain hospital environments, such as the tuberculosis isolation or operating rooms, can be extremely harmful for patients and/or hospital personnel. An important issue during the design of hospital facilities is an efficient airborne particle removal system. A near-optimal setup of the parameters that affect the airflow, and consequently the airborne particle trajectories within the room is desirable. Computational Fluid Dynamics (CFD) is an alternative to tedious and time-consuming experimental investigations during the design phase, when a large number of alternatives need to be evaluated. The main limitations of CFD application in building design are the high level of skill required, the complexity of the setup phase, and the difficulty of output data interpretation using common 2D (two-dimensional) display devices. A virtual reality (VR) environment can help in overcoming some of these limitations. A CFD/VR procedure for design of contaminant-free hospital facilities is presented in this paper. By means of a VR preprocessing step, inferior solutions can be discharged to drastically reduce the number of configurations to investigate. Then, a CFD/VR tool is used to explore the restricted set of room layouts. The 3D (three-dimensional), immersive visualisation of an indoor space and of the particle motion inside it allows the user to really see the particle flows and consequently understand the effects of room parameters on particle motion throughout the room. In this way a close-to-optimal configuration of the room layout and of the ventilation system can be achieved more speedily and more conveniently compared to traditional CFD investigations.

Removal of airborne particles by a tubular particle-removal device using UV/photoelectron method

A new tubular particle-removal device based on the principles of charging of particles by ions and collecting by electrical force is developed and its performance is evaluated. In this device, negative ions of a high concentration are generated from continuously supplied photoelectrons emitted from the surface of an Au/ITO (Indium Tin Oxide) thin film irradiated by UV light. This removal method is called UV/photoelectron method. Airborne particles fed into the device are designed to encounter the ions, and to be attracted to a cylindrical positive electrode of which the outer wall of the device is composed. Measurements using submicron aerosol particles show that over 90% of the particles of 0.06-0.12 μm in diameter are collected by the device when the operating flow rate is below 1 1 min −1 However, removal efficiency depends on particle size, aerosol flow rate and electric field strength in the device. To investigate theoretically the removal efficiency, numerical calculation of particle behavior is made in which simultaneous charging of particles by negative ions and particle transport by air flow, Brownian diffusion and Coulomb force are taken into account. The results calculated successfully reproduce the dependence of the results measured on the operating conditions of the device.