Detection Efficiency of a Water-Based TSI Condensation Particle Counter 3785

In this article we present observations on the detection efficiency of a recently developed TSI 3785 Water Condensation Particle Counter (WCPC). The instrument relies on activation of sampled particles by water condensation. The supersaturation is generated by directing a saturated airflow into a “growth tube,” in which the mass transfer of water vapor is faster than heat transfer. This results in supersaturated conditions with respect to water vapor in the centerline of a “growth tube.” In this study, the cut-off diameter, that is, the size, where 50% of the sampled particles are successfully activated, varied from 4 to 14 nm for silver particles as a function of temperature difference between the saturator and the growth tube. The solubility of the sampled particles to water played an important role in the detection efficiency. Cut-off diameters for ammonium sulphate and sodium chloride particles were 5.1 and 3.6–3.8 nm, respectively at nominal operation conditions. Corresponding cut-off diameter for hydrophobic silver particles was 5.8 nm.     

Performance Evaluation of a Fiber Length Classifier

A performance evaluation was conducted on a differential mobility classifier that separates fibers according to length using dielectrophoresis. The classifier had been constructed and used for several applications in previous studies. The performance of the classifier was predicted using a two-dimensional axisymmetric model of the flow field and then calculating particle trajectories for a variety of conditions. Based on the flow calculations, several regions of the classifier were improved to reduce likelihood of turbulent losses. For a given total flow through the classifier and a maximum voltage across the electrodes, the performance of the classifier was found to depend on the ratios of the aerosol flow to the inner and the outer sheath flows. It was found that the minimum classifiable length, the minimum length distribution width, and the throughput of classified fibers can each be optimized, but not independently. Several approaches to testing the resolution of the classifier were tried. The first was to measure the length distribution of fibers passing through the classifier under different conditions using electron microscopy. However, this was a slow and imprecise measure of performance. Two approaches using monodisperse latex spheres were used; one operated the instrument as an electrical mobility (electrophoresis) analyzer and the other evaluated only the flow system accuracy. All measures indicate that the classifier operates close to theoretical performance, but improvements are still possible. Suggested improvements require redesign of the flow system and improved electrode alignment.     

A Dilution Stack Sampler for Collection of Organic Aerosol Emissions: Design,Characterization and Field Tests

A dilution stack sampler specifically intended to collect fine organic aerosol from combustion sources while minimizing sample contamination has been designed and tested. The sampler simulates the cooling and dilution processes that occur in the plume downwind of a combustion source, so that the organic compounds which condense under ambient conditions will be collected as particulate matter. The special features of this sampler are described in detail, and compared with other stack sampling systems. The results of both laboratory and field tests of the system are discussed. Collection of organic aerosol using this sampler is compared with collection using EPA Method 5.     

Source Apportionment of Individual Carbonaceous Particles Using 14C and Laser Microprobe Mass Spectrometry

An exploratory study of laser microprobe mass spectra of individual atmospheric soot particles has been made in search of a potential combustion source tracer index. A tentative “cluster ratio index” (CRI = C₄ ^?/C₂ ^?) has been found and compared with bulk measurements of ¹⁴C in a set of ambient samples exhibiting varying impacts from woodburning and motor vehicle exhaust. A CRI-¹⁴C calibration curve resulted, and it led to the conclusion that, at the present level of precision, three particles (or agglomerates) of micrometer size or about 3 pg of carbon would be required for discrimination between the two pure sources. Mixture samples, such as those reported here, would require about 40 times as much. Classification of small set of individual particles from the mixed source ambient samples, suggests preservation of carbonaceous source identity at the single particle level.     

A Cough Aerosol Simulator for the Study of Disease Transmission by Human Cough-Generated Aerosols

Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of cough aerosol particles in the spread of disease and the efficacy of different types of protective measures, we constructed a cough aerosol simulator that produces a human-like cough in a controlled environment. The simulated cough has a 4.2 l volume and is based on coughs recorded from influenza patients. In one configuration, the simulator produces a cough aerosol containing particles from 0.1 to 100 μm in diameter with a volume median diameter (VMD) of 8.5 μm and a geometric standard deviation (GSD) of 2.9. In a second configuration, the cough aerosol has a size range of 0.1–30 μm, a VMD of 3.4 μm, and a GSD of 2.3. The total aerosol volume expelled during each cough is 68 μl. By generating a controlled and reproducible artificial cough, the simulator allows us to test different ventilation, disinfection, and personal protection scenarios. The system can be used with live pathogens, including influenza virus, which allows isolation precautions used in the healthcare field to be tested without risk of exposure for workers or patients. The information gained from tests with the simulator will help to better understand the transmission of infectious diseases, develop improved techniques for infection control, and improve safety for healthcare workers and patients.

Copyright 2013 American Association for Aerosol Research     

Vaporization--Condensation Generation of Ultrafine Hydrocarbon Particulate Matter for Inhalation Toxicology Studies

An evaporation/condensation particle generator produced 30-50 nm count median diameter particles from both pure hydrocarbons and from a complex mixture--used motor oil--at a concentration above 1 2 10 6 /cm 3 . The objective was to generate ultrafine aerosols for inhalation toxicology studies using specified organic components as surrogates for the particulate emissions generated by diesel internal combustion engines. This nanoparticle generation system, assembled from commercially available components, produced smaller particle size and higher particle number concentration than has been previously documented using Sinclair-La Mer condensation generator technology. The paper describes both the experiments used to design and characterize the particle generator and the operating conditions used for a specific inhalation experiment as an example of the system capability.     

Functional copolymer/organo-MMT nanoarchitectures: self-assembled core-shell morphology of poly(maleic anhydride-alt-α-olefin)/organo-MMT nanocomposites

This work describes the TEM morphology analysis of amphiphilic alternating copolymers of maleic anhydride (MA) with different α-olefins (1-hexene, 1-octene, 1-dodecene) synthesized by radical-initiated intercalative copolymerization of preintercalated MA···organoclay complexes in the presence of two types of organoclay such as reactive octadecyl amine-montmorillonite (ODA-MMT) and nonreactive dimethyldidodecyl ammonium-MMT (DMDA-MMT). TEM analyses of all the nanocomposites indicate the formation of symmetric or non-symmetric core-shell morphologies. Energy dispersive X-ray spectroscopy analyses were used to study the occurrence of the element in the poly(MA-alt-α-olefin)/organo-montmorillonite nanocomposites. A role of surfactant in these nanosystems insists on alternating copolymer segments with given hydrophobic/hydrophilic balance and surface organo-modifiers of MMT clays. Highly organized self-assembly with symmetric core-shell morphology were formed in nanosystems prepared in the presence of DMDA-MMT clay as compared with ODA-MMT clay-containing nanosystems. The relatively long branched olefin fragments significantly improve image parameters of core-shell morphology where some of the core structures contain accumulated and finely dispersed silicate particles at nano level around 2–25 nm. This observed phenomenon has brought a new approach for future utilization of these nanosystems in controlled drug delivery and anticancer applications with essentially prolonged activity.