Comparative Testing and Evaluation of Nine Different Air Samplers: End-to-End Sampling Efficiencies as Specific Performance Measurements for Bioaerosol Applications

Accurate exposure assessments are needed to evaluate health hazards caused by airborne microorganisms and require air samplers that efficiently capture representative samples. This highlights the need for samplers with well-defined performance characteristics. While generic aerosol performance measurements are fundamental to evaluate/compare samplers, the added complexity caused by the diversity of microorganisms, especially in combination with cultivation-based analysis methods, may render such measurements inadequate to assess suitability for bioaerosols. Specific performance measurements that take into account the end-to-end sampling process, targeted bioaerosol and analysis method could help guide selection of air samplers.

Nine different samplers (impactors/impingers/cyclones/ electrostatic precipitators/filtration samplers) were subjected to comparative performance testing in this work. Their end-to-end cultivation-based biological sampling efficiencies (BSEs) and PCR-/microscopy-based physical sampling efficiencies (PSEs) relative to a reference sampler (BioSampler) were determined for gram-negative and gram-positive vegetative bacteria, bacterial spores, and viruses.

Significant differences were revealed among the samplers and shown to depend on the bioaerosol's stress–sensitivity and particle size. Samplers employing dry collection had lower BSEs for stress-sensitive bioaerosols than wet collection methods, while nonfilter-based samplers showed reduced PSEs for 1 μm compared to 4 μm bioaerosols. Several samplers were shown to underestimate bioaerosol concentration levels relative to the BioSampler due to having lower sampling efficiencies, although they generally obtained samples that were more concentrated due to having higher concentration factors.

Our work may help increase user awareness about important performance criteria for bioaerosol sampling, which could contribute to methodological harmonization/standardization and result in more reliable exposure assessments for airborne pathogens and other bioaerosols of interest.

Copyright 2014 American Association for Aerosol Research     

Droplet-based microfluidics detector for bioaerosol detection

Detection of bioaerosols is important in fields ranging from environmental health monitoring to biosurveillance, and current detector weaknesses have motivated the development of new technologies. In this work, a detector was built, which applies the principles of droplet microfluidics to bioaerosol detection. Droplet microfluidics is a subfield of microfluidics based on the creation of monodisperse microdroplets with compartmentalized reagents and supports enhanced assays and fluidic manipulations. The bioaerosol detector operates by aerodynamically focusing aerosols directly into these droplets to harness the benefits of the microreactor environment. A breadboard detector system, which consisted of an aerodynamic focusing lens, aerosol-focusing capillary, microfluidic droplet chip, and optical microscope, was constructed. Computational fluid dynamic simulations and Lagrangian particle tracking modeling were conducted to identify the optimal conditions for focusing. Preliminary experiments, where aerosols were deposited onto a solid substrate, demonstrated sub 200-µm spot diameters for aerodynamic diameters of 2–5 µm. Test aerosols were then generated, and collected into the microfluidic liquid interface on the chip as verified by microscopy. Recovery efficiency of the aerosols was dependent on aerosol size and ranged from about 27% to nearly 100%. Finally, to prove bioaerosol collection and detection, a droplet propidium iodide (PI) assay was performed: the system distinguished between E. coli and non-biological aerosols within 20 s. Overall, this work established the technique of direct collection of bioaerosols into a convenient droplet microfluidic platform for detection.

Copyright © 2017 The Johns Hopkins University Applied Physics Laboratory     

Application of a quaternary ammonium agent on surgical face masks before use for pre-decontamination of nosocomial infection-related bioaerosols

Surgical face masks are commonly used by the general public in indoor environments. However, masks could be contaminated, resulting in secondary microbial infections when they act as touchable fomites. Therefore, we evaluated the ability and durability of a covalently bound antimicrobial surfactant coated onto mask surfaces before use to reduce the bacterial burden upon exposure to aerosols. With regard to bacteria that settled onto the mask surface, this antimicrobial product provided >99.3% efficiency for all three tested bacterial species. In addition, the antimicrobial ability of the coated mask maintained efficacy at least one week after coating. For bioaerosols that came into contact with the mask (10³ CFU/m³), the antimicrobial agent reduced the average colony rates by 91.8%, but the rates decreased with increased bioaerosol concentrations. Moreover, regardless of whether the coated mask was processed with the bioaerosol penetration test or the National Institute for Occupational Safety and Health-certified sodium chloride aerosol test, the filtration performance of the surgical mask was not significantly altered. These results demonstrate that this antimicrobial product has a durable inhibitory activity for the reduction of bacterial burdens on masks.

Copyright © 2016 American Association for Aerosol Research     

Pulsed ultraviolet light decontamination of virus-laden airstreams

Continuous ultraviolet germicidal irradiation (UVGI) has been extensively studied, but research on pulsed UVGI (PUVGI) is lacking and has primarily focused on disinfection of solid surfaces or liquids. This study addressed the gap in knowledge on the effectiveness of pulsed UVGI for disinfecting virus-laden calm air, with relevance to indoor rooms. Φ6 bacteriophage (a surrogate used to study communicable enveloped human respiratory viral pathogens such as influenza virus) was aerosolized by a Collison device into an enclosed test chamber, wherein the bioaerosol was exposed to PUVGI. The spectral content and performance of a pulsed white light lamp with a substantial UVC component were defined. Pulsed UV exposure of 10 to 30 s resulted in a two-log reduction in viable recovered virus from filter membranes and cyclone-based samplers. The small differences in Φ6 survival, after 10 to 30 s of exposure, emphasized the difficulty of complete eradication. However, exposure to 10 s of PUVGI resulted in significant reduction of virus viability. The dose–response displayed clear regimes of fast and slow exponential decay. Susceptibility factor for the fast-decay regime of aerosolized Φ6 (Z = 0.24 m²/J) was similar to those reported for influenza A virus aerosols at similar relative humidity. Our study demonstrated the potency of PUVGI against a viral bioaerosol. This has potential implications for the control of infectious bioaerosols in the healthcare setting.

© 2017 American Association for Aerosol Research     

Performance of Two Fluorescence-Based Real-Time Bioaerosol Detectors: BioScout vs. UVAPS

A 405 nm diode laser-based on-line bioaerosol detector, BioScout, was tested and compared with the Ultraviolet Aerodynamic Particle Sizer (UVAPS). Both instruments are based on laser-induced fluorescence of particles. Only a fraction of microbial particles produce enough fluorescence light to be detected by the instruments. This fluorescent particle fraction (FPF) is aerosol and instrument specific. The FPF values for common bacterial and fungal spores and biochemical particles were experimentally determined for both instruments. The BioScout exhibited higher FPF values for all the test aerosols except coenzyme NADH. The difference was higher for smaller particles. The FPF values of fungal spores and bacteria varied between 0.34 to 0.77 and 0.13 to 0.54 for the BioScout and the UVAPS, respectively. The results indicate that the 405 nm diode laser is a useful excitation source for fluorescence-based real-time detection of microbial aerosols. The FPF results of this study can be utilized to estimate the actual concentrations of bacterial and fungal spores in fluorescence-based ambient measurements.

Copyright 2014 American Association for Aerosol Research     

Recent Advances in Flame Retardancy of Polymeric Materials (Materials,Applications, Industry Developments,Markets)

The Fifth Annual Conference on Flame Retardancy was held May 24–26, 1994, at the Ramada Plaza Hotel, Stamford, Connecticut, USA. The conference was organized by Business Communications Company, Inc., Norwalk, Connecticut (Company President, Mr. Louis Naturman; Conference Coordinator, Mrs. Sharon D. Faust). New materials (polymers, blends, composites), their applications, industry developments, and markets were considered. Specifically, the most important topics were:

Introduction of new technological achievements and development in the field of flame retardancy (FR)

Review of the current state of science and technology in FR

Review of applications and markets for FR products

Presentation of recent developments in local and global standardization and in testing technology

Discussion of toxicity and environmental issues

Provision of a unique opportunity for newcomers to FR research technology and marketing to become acquainted with the FR field in all its aspects

Discussion of halogen-based and non-halogen-based flame retardant chemicals, syngergism, intumescence, FR mechanisms, modeling, flame parameters, inherently FR polymers, and polymer blends     

MECHANISM OF CLASSIFICATION IN A STURTEVANT-TYPE AIR CLASSIFIER

The estimation of air velocity distributions and particle trajectories is inevitable to analyse the mechanism of classification, but the direct measurement of il is extremely difficult.

The authors, here report three dimensional air velocity distributions within the inside drum of model Sturtevant-type air classifier measured by a spherical five-holed Pitot-lube, and also two dimensional particle ejecting velocities on a model distributor determined by photography.

Using those results, the cut size calculated from particle trajectories in the classifier is compared with the experimental results and theoretical values.     

Field performance of a novel passive bioaerosol sampler using polarized ferroelectric polymer films

Passive bioaerosol samplers can improve environmental and health protection by enhancing the practicality and cost-effectiveness of air sampling. Here, we present the outdoor field testing of a novel, passive bioaerosol sampler, the Rutgers Electrostatic Passive Sampler (REPS), based on the use of polarized, ferroelectric polymer film (poly(vinylidene fluoride)). Four 10-day-long field campaigns were conducted to compare total (culturable + non-culturable) and culturable bioaerosol collection efficiencies of REPS to passive samplers (PTFE settling filters and agar settling plates). These collection efficiencies were calculated relative to performance of an active, reference Button Sampler. Compared to passive PTFE filters, which exclusively rely on gravitational particle deposition, REPS collected a seven-fold higher total microorganism quantity. Relative to the Button Sampler, REPS collected 25% of the total number of bacteria and fungi and 65% of the culturable bacteria. Furthermore, REPS achieved this performance without any air movers, pumps, batteries, or external power. Since the Button Samplers operated at 4 L/min, REPS was calibrated to have equivalent sampling rates of 2.6 L/min and 1.0 L/min for culturable bacteria and total microorganisms, respectively. These results suggest that REPS can passively collect airborne microorganisms, including culturable bacteria, with high efficiency over long-term sampling durations. REPS can provide better preservation of bacterial culturability because it has no active airflow, which desiccates microbes in active samplers. Since there are limited options available for long-term, unattended bioaerosol sampling, REPS can complement currently available bioaerosol sampling technologies for numerous environmental health applications, such as exposure assessment for epidemiology and monitoring aeroallergen trends.

© 2017 American Association for Aerosol Research     

Economics of Treating Waste Gases from an Air Stripping Tower Using Photochemically Generated Ozone

Air stripping towers have been recommended for the removal of volatile organic compounds (VOCs) in drinking water supply and industrial waste treatment systems. This technique removes VOCs economically in the liquid phase. It can, however, create adverse secondary environmental impacts by removing VOCs from the water and discharging them to the air.

A commonly proposed method for controlling .VOC emissions is filtration of the off-gas through adsorption of the stripped organics in the off-gas by granular activated carbon. The high incremental cost of this alternative has produced an interest in alternative control technologies.

One alternative currently available is based on short wavelength ultraviolet (UV) radiation. This technique combines the effects of ozone generation, free radical formation and photolysis of the contaminants to effectively control the VOC emissions. This technique is known as Advanced Photo Oxidation (APO)^R.

The cost for APO is $0.27/m³ for a 3.8 m³/hr contaminated water system. A system of this size is adequate for a groundwater decontamination project where a moderate length of time is available for restoration of the site. The cost of a conventional air stripping tower with Granular Activated Carbon (GAC) adsorption emissions control in this size range would be $0.40 to $0.45/m³ (J.M. Montgomery, 1986).

Additional testing will be required to fully develop design guidelines for different contaminants and larger systems. Another area for additional technical documentation is the application of this technique to the liquid phase oxidation of VOCs.     

The Use of Nonlinear Acoustics as an Energy-Efficient Technique for Aerosol Removal

This article is a feasibility study on using nonlinear acoustic effects, acoustic streaming and acoustic radiation pressure, for aerosol removal in an air duct. Unlike previous research, which used acoustics solely to cause aerosol agglomeration prior to aerosol removal in traditional duct collection systems, this article considers the acoustic streaming effect, which is significant but was previously neglected. Monodispersed polystyrene spheres with diameters ranging from 0.3 to 6 μm were tested. The proposed system removed 12–20% of the submicron aerosols and 25–32% of the micron aerosols when the airflow rate was approximately 90 L/min. Acoustic streaming introduces stagnation points on the surface of the air duct and removes the aerosols by deposition. Acoustic radiation pressure causes aerosols to form agglomerates. This enhances inertial impaction and/or gravitational sedimentation, which further enhances the removal efficiency of micron aerosols. The particle-removal efficiency is proportional to the duration that the aerosols are exposed to the acoustic field. The pressure drop due to the nonlinear acoustic effects is negligible; thus, power consumption is minimal. This system has the potential to be developed into an energy-efficient technique for aerosol removal.

Copyright 2014 American Association for Aerosol Research     

MEASUREMENT OF INTERFACIAL AREA AND MASS TRANSFER COEFFICIENTS BY CHEMICAL METHOD OF C02 ABSORPTION INTO AQUEOUS SOLUTIONS OF NaOH IN A MODEL COLUMN WITH EXPANDED METAL SHEET PACKING

The theory of gas absorption accompanied by fast pseudo-fast order reaction which considered dependences of diffusivity, kinetic constant and Henry's law constant on absolute temperature and ionic strength was used to obtain values of effective interfacial areas and mass transfer coefficients in gas and liquid phase.

Experimental measurement of carbon dioxide absorption from mixture with air was performed in a pilot-plant column with expanded metal sheet packing irrigated with sodium hydroxide solution.

Resulting liquid and gas-side mass transfer coefficients are compared with values obtained from physical Absorption measurement of carbon dioxide into water and with measurement of gas-side mass transfer coefficient for sulphur dioxide in the same column.

The differences between determined values are discussed.     

New Pilot Plant Studies at the Budapest Waterworks

The quality of water provided by the Budapest Waterworks should comply with the standards prescribed by the European Community. According to these provisions, on one of the major water-producing regions (Csepel Island), rows of wells of 60,000 m³/day yield have been closed recently, and in the immediate future further plants would have been closed because of the high iron and manganese content of the water.

The raw water obtained from 100 different wells will be purified by a water treatment plant of 150,000 m³/day capacity. Considering the high iron content (0.05–0.15 mg/L) and manganese content (0.05–0.2 mg/L), the raw water fails to comply with the requirements of the potable water standard.

Since 1990, over a period of three years, we conducted water purification experiments in several stages. In these, three methods of oxidizing as well as single and double layer open rapid filters were applied to oxidize the manganese (and, to a lesser extent, the water) present in dissolved form, resp., to destroy various living organisms.

In the course of the experiments, it became clear that the chlorine and chlorine + air methods are efficient in case of a small quantity of iron to be oxidized and only 20–25% of the dissolved manganese content could be oxidized.

Neither of the two methods could ensure firm management of microbiological and bacteriological characteristics. The best results were obtained by ozone oxidation, in which case the chemical oxidizing process was almost fully completed and even the chlorine-resistant living organisms could be destroyed.

On the basis of the experiments carried out, the investment program of the water treatment plant was worked out and the conditions of an international tender were compiled whose winner will be commissioned to build up the water works in the time period 1993–1996. One of the main steps of the proposed technology is the ozone treatment.     

The Photochemical Generation of Ozone : Present State–of–the–Art

This paper reflects an investigation of the feasibility of photochemical generation of ozone by irradiating gases containing oxygen with Hg lamps of the highest performance emitting the 185 nm line. Besides the expected photostationary equilibrium, determining factors for practical yields in ozone generation by the 185 nm wavelength are : the reactor and gas temperature, the reactor geometry, and the gas composition, as well as the pressure.

Further developments are expected in the field of lamp construction and also improvement of reactor geometry. A better knowledge of the aging of the lamps is required, as well as of the photochemical reactions of oxygen in the technologies applied.

Systems presently available are most promising for application on small scale or in areas of public water distribution which have no developed structure.

     

Controlling Blown Polyethylene Film Optical Properties

The conventional blown process imparts an inherent haze to the product. The percentage of haze varies with certain process variables:

1. Surface irregularities caused by melt flow phenomena

2. Crystallization behavior

3. Melt drawing phenomena in certain types of polyethylene     

Modeling of nonstationary processes during separation of multicomponent isotope mixtures

The article presents a mathematical model for calculation of nonstationary hydraulic and separation processes in a gas centrifuge (GC) cascade for separation of multicomponent isotope mixtures. The model has been applied to calculate the parameters of nonstationary processes in a GC cascade for separation of krypton, germanium and tungsten isotopes. As a result, the specifics of the excess holdup distribution along the cascade stages has been identified, and variations of the isotope concentrations in a nonstationary process have been revealed. The data obtained show that the proposed mathematical model is able to adequately describe nonstationary hydraulic processes in GC cascades for separation of multicomponent isotope mixtures.

Highlights:

Mathematical model of cascade for separation of multicomponent isotope mixture has been developed.

The model verification has been done.

The isotope transient regularities into cascade during nonstationary processes has been identified.     

Production of neutral molecular clusters by controlled neutralization of mobility standards

Measuring aerosols and molecular clusters below the 3 nm size limit is essential to increase our understanding of new particle formation. Instruments for the detection of sub-3 nm aerosols and clusters exist and need to be carefully calibrated and characterized. So far calibrations and laboratory tests have been carried out using mainly electrically charged aerosols, as they are easier to handle experimentally. However, the charging state of the cluster is an important variable to take into account. Furthermore, instrument characterization performed with charged aerosols could be biased, preventing a correct interpretation of data when electrically neutral sub-3 nm aerosols are involved. This article presents the first steps to generate electrically neutral molecular clusters as standards for calibration. We show two methods: One based on the neutralization of well-known molecular clusters (mobility standards) by ions generated in a switchable aerosol neutralizer. The second is based on the controlled neutralization of mobility standards with mobility standards of opposite polarity in a recombination cell. We highlight the challenges of these two techniques and, where possible, point out solutions. In addition, we give an outlook on the next steps toward generating well-defined neutral molecular clusters with a known chemical composition and concentration.

Published with license by American Association for Aerosol Research     

Measurement of the Nanoparticles Distribution in Flat and Pleated Filters During Clogging

It is currently admitted that for each filtration process using pleated filters, at least three steps can be distinguished: depth and surface filtration, which are common to flat filters, and surface reduction. This step is caused by inefficient filling of the pleat due to the filter geometry. For combustion aerosol, it has been proved that this third step strongly depends on the filtration velocity resulting in an increase of the resistance when air flow decreases. This observation leads one to think that Brownian diffusion, higher for low velocities, could influence the clogging dynamic of a pleated filter.

In this article, a protocol derived from the dust cake preparation method published by Schmidt is developed. The aim of this study is to measure the aerosol penetration inside a filter media as well as in a pleat using a scanning electronic microscope and energy dispersive X-ray spectroscopy elementary detection. This method has also been extended to the study of pleated filters to measure the particle distribution inside the pleat. Filters were loaded with nanoparticles in order to evaluate the specificity of the diffusional regime on the clogging of pleated HEPA filters. For pleated filters, two filtration velocities were investigated: 2.5 and 0.2 cm/s.

Copyright 2014 American Association for Aerosol Research     

Clogging of Industrial High Efficiency Particulate Air (HEPA) Filters in Case of Fire: From Analytical to Large-Scale Experiments

The Institute of Radioprotection and Nuclear Safety (IRSN in French) is conducting research on the impact of a fire on the behaviour of containment devices such as high efficiency particulate air (HEPA) pleated filters for radioactive materials. This work aims to study the clogging of HEPA filters in case of fire involving realistic materials (polymers making up gloves boxes, waste treatment solvent, hydraulic oil, solid material mixtures making up a trash bin, electrical cables, and cabinets) used in nuclear facilities, from the medium to large scale. The clogging kinetics of industrial pleated HEPA filters is monitored by measuring the pressure drop of the filters and the filtered air temperature at a given filtration velocity (from 0.23 to 2.1 cm/s). Upstream HEPA filters, combustion aerosols are characterized in terms of size distribution, mass concentration, composition, and particle morphology using, respectively, a DMS500 (Cambustion^LTD), glass fiber filter sampling, and transmission electron microscope analysis of particles deposited on TEM grids. Particles emitted denote well-known fractal morphology, are composed of carbonaceous primary particles with diameters ranging from 31 nm to 48 nm and showing an high clogging efficiency. An empirical relationship has been successfully applied to the obtained results for a larger range of fuels, filtration velocities and fire conditions.

Finally, experiments have been performed on a large-scale facility, using full-scale fire scenarios (electrical cabinet, constant, and variable filtration velocity) and a reasonable agreement was observed with our empirical relationship. At this scale, particles appear to be compact, with a complex composition and diameters close to 220 nm with a lower clogging efficiency.

Copyright 2014 American Association for Aerosol Research