Electrochemical dithiothreitol assay for large-scale particulate matter studies

Particulate matter (PM) air pollution is associated with human morbidity and mortality. Measuring PM oxidative potential has been shown to provide a predictive measurement between PM exposure and adverse health impacts. The dithiothreitol (DTT) assay is commonly used to measure the oxidative potential of PM_2.5 (PM less than 2.5?µm aerodynamic diameter). In the common, kinetic form of this assay, the decay of DTT is quantified over time (indirectly) using 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB, Ellman’s reagent) via UV/vis absorbance spectroscopy. The loss of DTT can also be quantified directly using electrochemical detection. The objectives of this work were (1) to evaluate the electrochemical assay, using commercially available equipment, relative to the UV/vis absorbance assay and (2) to apply the electrochemical method to a large (>100) number of PM_2.5 filter samples. Also presented here is the comparison of an endpoint assay to the kinetic assay, in an attempt to reduce the time, labor, and materials necessary to quantify PM oxidative potential. The endpoint, electrochemical assay gave comparable results to the UV/vis absorbance assay for PM_2.5 filter sample analysis. Finally, high filter mass loadings (higher than about 0.5?µg PM per mm² filter) lead to suboptimal DTT assay performance, which suggests future studies should limit particle mass loadings on filters.

Copyright © 2019 American Association for Aerosol Research     

Using the WIBS-4 (Waveband Integrated Bioaerosol Sensor) Technique for the On-Line Detection of Pollen Grains

Primary biological aerosol particles (PBAP) such as pollen and fungal spores can induce allergenic responses and affect health in general. Conditions such as allergic rhinitis (hay fever) and asthma have been related to pollen concentrations. Likewise some pollen have been shown to induce ice nucleation and cloud condensation at higher temperatures than those associated with some chemical species, thereby affecting planet Earth's albedo and overall radiative balance. Hence, the near real-time (on-line) monitoring of airborne pollen and other PBAP using a variety of spectroscopic and light scattering techniques represents an area of growing development and consequence.

In this study, two separate field campaigns (one at a rural site in Ireland and the other at an urbanized location in Germany) were performed to detect and quantify pollen releases using a novel on-line fluorescence spectrometer (WIBS-4). The results were compared with results obtained using more traditional Hirst-type impactors. Size, “shape,” and fluorescence characteristics of ambient particles were used to determine the concentrations and identity of the PBAP likely to be pollen grains.

The concentration results obtained for both methodologies at both the Irish and German sites correlated very well, with R ² values >0.9 determined for both campaigns. Furthermore, the sizing data available from the WIBS-4 approach employed in Ireland indicated that pollen grains can be identified in appropriate conditions. WIBS-4 measurements of Yew pollen both in the laboratory and at the rural site indicated almost identical size ranges of 25 to 27 μm. Yew pollen is generally reported to be in this range, but the measurements reported here are the first of their type providing data on the size of in-flight Yew pollen.

Copyright 2014 American Association for Aerosol Research     

Effect of different application techniques on microshear bond strength of self-etch adhesives to dentin

Objectives: To investigate the effect of different self-etch adhesive systems application techniques: active or passive in a single or double layer on adhesive–dentin microshear bond strength.

Methods: Occlusal surfaces of 48 extracted human molars were ground to expose flat superficial dentin surfaces. Specimens were randomly divided into two main groups according to the tested self-etch adhesive system either: One-step self-etch (Adper^TM easy-one) or two-step self-etch (Adper^TM SE Plus). Each adhesive system was applied on the prepared dentin surfaces followed one of these techniques: (1) Passive application of a single layer, (2) Active application of single layer, (3) Passive application of double adhesive layer (with light curing in between), and (4) Active application of double adhesive layers. Resin composite was packed inside micro-tubes fixed on the bonded dentin surfaces and light cured for 40 s. All specimens were stored in artificial saliva either for 24 h or 3 months before testing. Microshear bond strength test was employed using a universal testing machine at a crosshead speed of 0.5 mm/min.

Results: Adper^TM SE Plus showed higher significant microshear bond strength in compared with Adper^TM easy-one. For both adhesive systems active application showed higher significant microshear bond strength to dentin than passive application. Double application of adhesive systems showed lower microshear bond strength than single application.

Conclusion: Active application of self-etch adhesives could improve the dentin microshear bond strength. Double application with curing in between the layers did not improve the bond strength to the tested adhesive.     

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.     

Development of an aerosol mass spectrometer lens system for PM2.5

The aerodynamic lens system of the Aerodyne Aerosol Mass Spectrometer (AMS) was analyzed using the Aerodynamic Lens Calculator. Using this tool, key loss mechanisms were identified, and a new lens design that can extend the transmission of particulate matter up to 2.5 μm in diameter (PM2.5) was proposed. The new lens was fabricated and experimentally characterized. Test results indicate that this modification to the AMS lens can significantly improve the transmission of large sized particles, successfully achieving a high transmission efficiency up to PM2.5 range.

© 2016 American Association for Aerosol Research     

Residual monomer release from orthodontic adhesives cured with different light sources

Introduction: The aim of this study was to evaluate the residual monomer release from orthodontic adhesives cured with light-emitting diode (LED) and halogen light sources.

Methods: Seven hundred and twenty stainless steel brackets were divided into 3 groups according to the adhesive system used (Transbond XT light-cure adhesive [TXT], Transbond LR capsule [LR], and Light Bond light-cure adhesive paste [LB]), and each group was divided into 2 subgroups according to light-curing procedure (LED or halogen). Brackets were bonded with adhesives onto tooth buccal surfaces and polymerized. Each specimen contained 24 brackets that simulated the oral environment (n = 5). The specimens were immersed in a 75% ethanol/water solution at 37 °C for 10 min, 1 h, 1 d, 7 d, 14 d, and 30 d, respectively. Eluted monomers (Bis-GMA, UDMA, and TEGDMA) were detected using HPLC.

Results: There was residual monomer release at all time periods, and the highest amount of release was observed cumulatively on the 30th day. The cumulative Bis-GMA released from adhesives was not different (p > 0.05). The cumulative TEGDMA released from adhesives was statistically different (p < 0.05). There was no statistical difference between QTH and LED light-curing units for each adhesive (p > 0.05).

Conclusions: The release of residual monomers stays at a high level for a long time after polymerization. The total leaching of residual monomers from the Light Bond light-cure sealant resin plus Light Bond light-cure adhesive paste was higher than that of other materials for both curing units. Different curing units (LED or QTH) did not affect the monomer release from the orthodontic adhesives.     

The First Combined Thermal Desorption Aerosol Gas Chromatograph—Aerosol Mass Spectrometer (TAG-AMS)

To address the critical need for improving the chemical characterization of the organic composition of ambient particulate matter, we introduce a combined thermal desorption aerosol gas chromatograph—aerosol mass spectrometer (TAG-AMS). The TAG system provides in-situ speciation of organic chemicals in ambient aerosol particles with hourly time resolution for marker compounds indicative of sources and transformation processes. However, by itself the TAG cannot separate by particle size and it typically speciates and quantifies only a fraction of the organic aerosol (OA) mass. The AMS is a real-time, in-situ instrument that provides quantitative size distributions and mass loadings for ambient fine OA and major inorganic fractions; however, by itself the AMS has limited ability for identification of individual organic compounds due to the electron impact ionization detection scheme used without prior molecular separation.

The combined TAG-AMS system provides real-time detection by AMS followed by semicontinuous analysis of the TAG sample that was acquired during AMS operation, achieving simultaneous and complementary measurements of quantitative organic mass loading and detailed organic speciation. We have employed a high-resolution time-of-flight mass spectrometer (HR-ToF-MS) to enable elemental-level determination of OA oxidation state as measured on the AMS, and to allow improved compound identification and separation of unresolved complex mixtures (UCM) measured on the TAG. The TAG-AMS interface has been developed as an upgrade for existing AMS systems. Such measurements will improve the identification of organic constituents of ambient aerosol and contribute to the ability of atmospheric chemistry models to predict ambient aerosol composition and loadings.

Copyright 2014 American Association for Aerosol Research     

Dihydrogen Catalysis: A Remarkable Avenue in the Reactivity of Molecular Hydrogen

Molecular hydrogen is the simplest and most abundant compound in the universe and is involved in numerous industrial chemical processes. In conventional chemistry, dihydrogen typically plays the role of a reductant and a reagent for homogeneous and heterogeneous hydrogenation processes such as the industrial and enzymatic ammonia formation, reduction of metallic ores and hydrogenation of unsaturated fats and oils. However, there are also processes in which molecular hydrogen participates as promoter, and even as catalyst. The catalytic role of the dihydrogen in free-valence migration in irradiated polymers and the interstellar isomerization of the formyl cation (protonated carbon monoxide) are well-documented examples of such processes. Recently, this issue has received new attention. Dihydrogen has been shown to play the role of a dehydrogenation catalyst (involving particularly metallocomplexes and inorganic materials), a relay (pass-on) transfer molecular agent and a transporter of protons.

This review article, combined with original results, is focused on the mechanisms of the chemical processes where dihydrogen demonstrates catalytic behavior. We will call these processes (with somewhat broader meaning of the term) “dihydrogen catalysis” (DHC) which also includes the reactions mediated by transition metal dihydrides. Dihydrides are tentatively considered as pre-activated dihydrogen, coordinated to a metal center or implanted into a solid surface/support.

DHC reactions are classified into five major reaction types: (i) dihydrogen-assisted relay transport of H-atoms (H2-RT); (ii) dihydrogen-assisted stepwise relay transport of H-atoms or of a free valence (sH2-RT); (iii) dihydrogen-assisted proton transport (H2-PT); (iv) dihydrogen-assisted dehydrogenation (H2-DeH); and (v) pre-activated dehydrogenation (PA-DeH). The classification of these mechanisms is based on a detailed analysis of numerous potential energy surfaces studied by DFT and ab initio methods in conjunction with available experimental data. The H2-RT, H2-DeH, and PA-DeH processes occur via cyclic transition states. The relay H2-RT transport involves the H-H-H triad linked to both H-donor and H-acceptor centers, whereas the transition state ring in the H2-DeH dehydrogenation processes involves a H-H-H-H tetrad with the dihydrogen catalyst located in the middle. The H2-PT mechanism provides the transport of a proton mediated by dihydrogen combined in a triangular (H₃⁺)-carrier unit.

There are also practically important processes stimulated by dihydrogen such as the hydrogen spillover and hydrogen build-up in electronics, in which the catalytic role of dihydrogen is ambiguous, either because of the uncertainties in mechanisms, or prevailing traditional views. Some examples are briefly discussed in the framework of the concept of dihydrogen catalysis, some being provided with theoretical support (in part calculated by us), and others being merely hypothesized to provide suggestions to an interested reader.     

Effect of potassium on a model soot combustion: Raman and HRTEM evidences

The effect of potassium on the oxidation of a model carbonaceous material (Printex U, namely, soot for brevity) has been investigated under isothermal conditions. For this purpose, Raman spectroscopy, Transmission Electron Microscopy (TEM), and Brunaure, Emmet, Teller surface area characterization have been applied to investigate structural changes occurring during soot oxidation both in the presence and in the absence of potassium. The Raman spectra of the model soot during combustion showed that oxidation preferentially involves the amorphous carbon fraction of the soot and only subsequently it affects the more ordered sp² domains. However, in the K-doped Printex U the oxidation of both the amorphous and more ordered sp² structures occurs concurrently. These findings have been confirmed by TEM analysis and explain the observed higher combustion activity of K-containing sample.

Copyright © 2016 American Association for Aerosol Research     

Biological Filtration for Ozone and Chlorine DBP Removal

This paper presents results from a water treatment pilot testing program in Winnipeg, Canada (pop. 650,000) which evaluated a DAF/ozone/deep bed filtration process. As part of the testing program, biological filtration using GAC and anthracite media was assessed for the removal of ozone DBPs and background chlorine DBPs (due to upstream chlorination of the source water). The results were used to evaluate the effectiveness of biological filtration for DBP removal.

High filtration rates were tested in this study. The 2.1m deep filters were run at a hydraulic loading rate (HLR) of 35 m/h with an empty bed contact time (EBCT) of only 3.6 minutes.

The important findings of this work are

?The high-rate biologically active carbon (BAC) filters met the objective of controlling ozone DBPs. These results confirm that high rate, low EBCT filters can provide significant biodegradation. Anthracite biofilters provided significantly less removal of ozone DBPs.

?The high rate BAC filters showed significant reduction of background HAAs. BAC reduced the background HAAs to below the long-term target of 30 μg/L. Anthracite biofilters did not exhibit HAA removal.

?Biological filtration with either media was ineffective for background THM removal. The long-term target of 40 μg/L could not be achieved without GAC adsorption.     

NaOCl degradation of one-step one-bottle self-etch adhesives bonded to bovine dentine

Objective: The aim of the present study was to assess the influence of an in vitro aging regime (NaOCl storage) on dentine microtensile bond strength (μTBS) of five one-step one-bottle self-etch adhesives in comparison with bond strength of two-step self-etch adhesive.

Material and methods: Flattened dentine surfaces from 30 bovine incisors were bonded with five one-step one-bottle self-etch adhesives (iBond, Clearfil S3 Bond, AdheSE One F, G-Bond, Optibond all-in-one) and one two-step self-etching adhesive (Clearfil SE Bond). Composite buildups were done with microhybrid resin composite. Bonded samples were sectioned into resin–dentine sticks of 0.8 mm² cross section. Randomly selected 20 sticks were tested directly by microtensile bond strength testing machine, whereas another randomly selected 20 sticks were tested after being stored in solution of 10% NaOCl for 5 h. Data were analyzed by two-way analysis of variance (ANOVA) and Tukey’s honest significant difference (HSD) tests (p < 0.05).

Results: All adhesives exhibited similar dentine bond strength with exception of G-Bond. After NaOCl storage, μTBS reduced in all groups significantly. The lowest μTBS were found for G-Bond. Rest of one-step self-etch adhesives presented similar μTBS with two-step self-etch adhesive.

Conclusion: Interfaces of resin–dentine bonding are susceptible to NaOCl degradation. The amount of the destruction depends on adhesive system. NaOCl degradation of the nonresin encapsulated collagen fibers might decrease long-term stability of resin bonding with dentine.     

Development and field evaluation of an online monitor for near-continuous measurement of iron,manganese, and chromium in coarse airborne particulate matter (PM)

A novel air sampling monitor was developed for near-continuous (i.e., 2-h time resolution) measurement of iron (Fe), manganese (Mn), and chromium (Cr) concentrations in ambient coarse particulate matter (PM) (i.e., PM_10–2.5). The developed monitor consists of two modules: (1) the coarse PM collection module, utilizing two virtual impactors (VIs) connected to a modified BioSampler to collect ambient coarse PM into aqueous slurry samples; (2) the metal concentration measurement module, which quantifies the light absorption of colored complexes formed through the reactions between the soluble and solubilized target metals and pertinent analytical reagents in the collected slurries using a micro volume flow cell (MVFC) coupled with UV/VIS spectrophotometry. The developed monitor was deployed in the field for continuous ambient PM collection and measurements from January to April 2016 to evaluate its performance and reliability. Overall, the developed monitor could achieve accurate and reliable measurements of the trace metals Fe, Mn, and Cr over long sampling periods, based on the agreement between the metal concentrations measured via this online monitor and off-line parallel measurements obtained using filter samplers. Based on our results, it can be concluded that the developed monitor is a promising technology for near-continuous measurements of metal concentrations in ambient coarse PM. Moreover, this monitor can be readily configured to measure the speciation (i.e., water-soluble portion as well as specific oxidation states) of these metal species. These unique abilities are essential tools in investigations of sources and atmospheric processes influencing the concentrations of these redox-active metals in coarse PM.

Copyright © 2016 American Association for Aerosol Research     

Particulate matter characteristics,dynamics, and sources in an underground mine

Particulate matter (PM) from mining operations, engines, and ore processing may have adverse effects on health and well-being of workers and population living nearby. In this study, the characteristics of PM in an underground chrome mine were investigated in Kemi, Northern Finland. The concentrations and chemical composition of PM in size ranges from 2.5 nm to 10 µm were explored in order to identify sources, formation mechanisms, and post-emission processes of particles in the mine air. This was done by using several online instruments with high time-resolution and offline particulate sampling followed by elemental and ionic analyses. A majority of sub-micrometer particles (<1 µm in diameter, PM₁) originated from diesel engine emissions that were responsible for a rather stable composition of PM₁ in the mine air. Another sub-micrometer particle type originated from the combustion products of explosives (e.g., nitrate and ammonium). On average, PM₁ in the mine was composed of 62%, 30%, and 8% of organic matter, black carbon, and major inorganic species, respectively. Regarding the analyzed elements (e.g., Al, Si, Fe, Ca), many of them peaked at >1 µm indicating mineral dust origin. The average particle number concentration in the mine was (2.3 ± 1.4)*10⁴ #/cm³. The maximum of particle number size distribution was between 30 and 200 nm for most of the time but there was frequently a distinct mode <30 nm. The potential origin of nano-size particles remained as challenge for future studies.

Copyright © 2018 The Authors. Published with license by Taylor & Francis     

Highly sensitive nano-aerosol detection based on the whispering-gallery-mode in cylindrical optical fiber resonators

Highly sensitive detection of nanoscale aerosols, or nano-aerosols, is a difficult challenge. Here, we report a fiber optical technique that is capable of detecting trace-level nano-aerosols. Our method is based on monitoring the nano-aerosol-induced resonance shift due to the optical Whispering-Gallery-Mode (WGM) in a cylindrical optical fiber resonator. A nearly linear relationship between the WGM resonance shift and the aerosol coverage ratio of silica nanoparticles (40–50 nm dia.) on the fiber resonator was identified in the low coverage regime. Our experimental results imply sensitivity at the level of ～2 nanoparticles per μm² deposited on the fiber resonator, which corresponds to pg-level sensitivity in the total aerosol mass within the effective detection area. The response of this fiber optical sensor is further confirmed by using silica nanoparticles deposited on the fiber surface via electrostatic self-assembly. The fiber optical technique for nanoparticle detection may ultimately lead to an instrument capable of real-time in situ aerosol detection with ultrahigh sensitivity.

Copyright © 2016 American Association for Aerosol Research     

A novel high-volume Photochemical Emission Aging flow tube Reactor (PEAR)

Aerosols emitted from various anthropogenic and natural sources undergo constant physicochemical transformations in the atmosphere, altering their impacts on health and climate. This article presents the design and characteristics of a novel Photochemical Emission Aging flow tube Reactor (PEAR). The PEAR was designed to provide sufficient aerosol mass and flow for simultaneous measurement of the physicochemical properties of aged aerosols and emission exposure studies (in vivo and in vitro). The performance of the PEAR was evaluated by using common precursors of secondary aerosols as well as combustion emissions from a wood stove and a gasoline engine. The PEAR was found to provide a near laminar flow profile, negligible particle losses for particle sizes above 40?nm, and a narrow residence time distribution. These characteristics enable resolution of temporal emission patterns from dynamic emission sources such as small-scale wood combustion. The formation of secondary organic aerosols (SOA) in the PEAR was found to be similar to SOA formation in a smog chamber when toluene and logwood combustion emissions were used as aerosol sources. The aerosol mass spectra obtained from the PEAR and smog-chamber were highly similar when wood combustion was used as the emission source. In conclusion, the PEAR was found to plausibly simulate the photochemical aging of organic aerosols with high flow rates, needed for studies to investigate the effects of aged aerosols on human health. The method also enables to study the aging of different emission phases in high time resolution, and with different OH-radical exposures up to conditions representing long-range transported aerosols.

Copyright © 2019 American Association for Aerosol Research     

Numerical modeling of the performance of high flow DMAs to classify sub-2 nm particles

While there are several computational studies on differential mobility analyzers (DMA), there is none for high flow DMA to classify nanoparticles less than 3?nm. A specific design of a high flow DMA, a half mini DMA, is investigated to predict its performance through numerical modeling in the incompressible flow regime. The governing equations for flow field, electric field and aerosol transport are solved using COMSOL 5.3. The transfer function of the half mini DMA is compared with that of a nano DMA (TSI 3085). The results show that both the height of the transfer function and resolution (R) of the half mini DMA are much better than those of nano DMA in sub-2?nm particle size range. Finally, the transfer function of half mini DMA is evaluated for different values of aerosol flow rate to the sheath flow rate (q/Q). Comparison of the simulated transfer function with existing models from Knutson–Whitby and Stolzenburg is also elucidated. It is found that the former model overestimates the resolution; whereas the latter is close to the simulation results for q/Q above 0.067. This work provides a useful method to study the flow regimes and transfer function of a high flow DMA.

Copyright © 2018 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.     

Real-time separation of aerosolized Staphylococcus epidermidis and polystyrene latex particles with similar size distributions

For rapid and effective detection of airborne microorganisms, it is preferable to remove dust particles during the air sampling process because they can reduce the detection accuracy of measurements. In this study, a methodology of real-time separation ofaerosolized Staphylococcus epidermidis (S. epidermidis) andpolystyrene latex (PSL) particles of similar size was investigated. These two species represent biological and non-biological particles, respectively. Due to their different relative permittivities, they grasp different numbers of air ions under corona discharge. After these charged particles enter a mobility analyzer with airflow, in which an electric field is applied perpendicular to the airflow, the S. epidermidis and PSL particles separate, due to the difference in their electric mobilities, and exit through two different outlets. Purities and recoveries for S. epidermidis and PSLat their respective outlets were determined with measurements of aerosol number concentrations and ATP bioluminescence intensities at the inlet and two outlets. The results were that purities for PSL and S. epidermidis were 70% and 80%, respectively. This methodology provides a rapid and simple way to increase the detection accuracy of bacterial agents in air.

Copyright © 2017 American Association for Aerosol Research     

Design and evaluation of an aerodynamic focusing micro-well aerosol collector

Aerosol sampling and identification is vital for the assessment and control of particulate matter pollution, airborne pathogens, allergens, and toxins and their effect on air quality, human health, and climate change. In situ analysis of chemical and biological airborne components of aerosols on a conventional filter is challenging due to dilute samples in a large collection region. We present the design and evaluation of a micro-well (µ-well) aerosol collector for the assessment of airborne particulate matter (PM) in the 0.5–3 µm size range. The design minimizes particle collection areas allowing for in situ optical analysis and provides an increased limit of detection for liquid-based assays due to the high concentrations of analytes in the elution/analysis volume. The design of the collector is guided by computational fluid dynamics (CFD) modeling; it combines an aerodynamic concentrator inlet that focuses the aspirated aerosol into a narrow beam and a µ-well collector that limits the particle collection area to the µ-well volume. The optimization of the collector geometry and the operational conditions result in high concentrations of collected PM in the submillimeter region inside the µ-well. Collection efficiency experiments are performed in the aerosol chamber using fluorescent polystyrene microspheres to determine the performance of the collector as a function of particle size and sampling flow rate. The collector has the maximum collection efficiency of about 75% for 1 µm particles for the flow rate of 1 slpm. Particles bigger than 1 µm have lower collection efficiencies because of particle bounce and particle loss in the aerodynamic focusing inlet. Collected samples can be eluted from the device using standard pipettes, with an elution volume of 10–20 µL. The transparent collection substrate and the distinct collection region, independent of particle size, allows for in situ optical analysis of the collected PM.

© 2017 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