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ABSTRACT. An earlier study evaluated the physical performance of the Swirling Aerosol Collector, also known as the``BioSampler,'' and found it to have several advantages over the widely used AGI-30 impinger when tested with inert test particles. Th e present study was focused on the ph ysical and biological performan ce with laboratory-aerosolized microorganisms. The results showed th at the BioSampler has better physical collection ef® ciency for B. subtilis an d P.¯uo-rescens than the AGI-30 wh en water was used as the collection¯uid an d the sampling¯ow rate ranged from 8.5 L min I 1 to the standard 12.5 L min I 1 . Additionally, the BioSampler provided equivalent or better microbial recovery for the 2 species than the AGI-30 did. The swirling motion of the collection liquid in the BioSampler generates very few bubbles and therefore causes minimal reentrainment of already collected microorganisms. In contrast to the AGI-30, the BioSampler can be used very effectively with nonevaporating liquids, such as mineral oil or glycerol. Mineral oil was found to be a suitable collection¯uid for culture an alysis, wh ereas glycerol can be used only for non culture assays, such as the polymerase chain reaction. By using a more viscous, nonevaporating¯uid, the BioSampler can be used for long-term sampling of low airborne bacterial concentrations, while the AGI-30 impinger, ® lled with a standard evaporating¯uid, can only be used for up to abou t 30 min.

Recently, nanometer-sized aluminum powders became available commercially, and their use as potential additives to propellants, explosives, and pyrotechnics has attracted significant interest. It has been suggested that very low melting temperatures are expected for nanosized aluminum powders and that such low melting temperatures could accelerate oxidation and trigger ignition much earlier than for regular, micron-sized aluminum powders. The objective of this work was to investigate experimentally the melting and oxidation behavior of nanosized aluminum powders. Powder samples with three different nominal sizes of 44, 80, and 121 nm were provided by Nanotechnologies Inc. The particle size distributions were measured using small-angle X-ray scattering. Melting was studied by differential scanning calorimetry where the powders were heated from room temperature to 750 degrees C in an argon environment. Thermogravimetric analysis was used to measure the mass increase indicative of oxidation while the powders were heated in an oxygen-argon gas mixture. The measured melting curves were compared to those computed using the experimental particle size distributions and thermodynamic models describing the melting temperature and enthalpy as functions of the particle size. The melting behavior predicted by different models correlated with the experimental observations only qualitatively. Characteristic stepwise oxidation was observed for all studied nanopowders. The observed oxidation behavior was well interpreted considering the recently established kinetics of oxidation of micron-sized aluminum powders. No correlation was found between the melting and oxidation of aluminum nanopowders.

Ionic air purifiers have become increasingly popular for removing dust particles, aeroallergens and airborne microorganisms from indoor air in various settings. While the indoor air cleaning effect, resulting from unipolar and bipolar ion emission, has been tested by several investigators, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. Among the five tested ionic air purifiers (two wearable and three stationary) producing unipolar air ions, the units with a higher ion emission rate provided higher particle removal efficiency. The ion polarity (negative vs. positive), the particle size (0.3-3 microm) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria), as well as the body temperature and breathing did not considerable affected the ionization-driven particle removal. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when they are used inside confined spaces with a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms, and animal confinements). Based on our experiments, we proposed that purifiers with a very high ion emission rate be operated in an intermittent mode if used indoors for extended time periods. As the particles migrate to and deposit on indoor surfaces during the operation of ionic air purifiers, some excessive surface contamination may occur, which introduces the need of periodic cleaning these surfaces.