Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

A laboratory system was constructed that allows the super-micron particles to be aged for long periods of time under conditions that can simulate a range of natural environments and conditions, including relative humidity, oxidizing chemicals, organics and simulated solar radiation. Two proof-of-concept experiments using a non-biological simulant for biological particles and a biological simulant demonstrate the utility of these types of aging experiments. Green Visolite®, which is often used as a tracer material for model validation experiments, does not degrade with exposure to simulated solar radiation, the actual biological material does. This would indicate that Visolite® should be a good tracer compound for mapping the extent of a biological release using fluorescence as an indicator, but that it should not be used to simulate the decay of a biological particle when exposed to sunlight. The decay in the fluorescence measured for B. thurengiensis is similar to what has been previously observed in outdoor environments.

A unique aerosol flow chamber coupled with a bistatic LIDAR system was implemented to measure the optical scattering cross sections and depolarization ratio of common atmospheric particulates. Each of seven particle types (ammonium sulfate, ammonium nitrate, sodium chloride, potassium chloride, black carbon and Arizona road dust) was aged by three anthropogenically relevant mechanisms: 1. Sulfuric acid deposition, 2. Toluene ozonolysis reactions, and 3. m-Xylene ozonolysis reactions. The results of pure particle scattering properties were compared with their aged equivalents. Results show that as most particles age under industrial plume conditions, their scattering cross sections are similar to pure black carbon, which has significant impacts to our understanding of aerosol impacts on climate. In addition, evidence emerges that suggest chloride-containing aerosols are chemically altered during the organic aging process. Here we present the direct measured scattering cross section and depolarization ratios for pure and aged atmospheric particulates.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Fibrous filter pressure drop and aerosol collection efficiency were measured at low air pressures (0.2-0.8 atm) and high face velocities (5-19 m/s) to give fiber Reynolds numbers lying in the viscous-inertial transition flow regime (1-15). In this regime, contemporary filtration theory based on Kuwabara's viscous flow through an ensemble of fibers underpredicts single fiber impaction by several orders of magnitude. Streamline curvature increases substantially as air stream inertial forces become significant. Dimensionless pressure drop measurements followed the viscous-inertial theory of Robinson and Franklin (1972) rather than Darcy's linear pressure-velocity relationship. Sodium chloride and iron nano-agglomerate aerosols were tested to provide a comparison between particles of dissimilar densities and shape factors. Total filter efficiency collapsed when plotted against the particle Stokes number and fiber Reynolds number. Efficiencies were then modeled with an impactor type equation where the cutpoint Stokes number and a steepness parameter described data well in the sharply increasing portion of the curve (20%-80% efficiency). A minimum in collection efficiency was observed at small Stokes numbers and attributed to interception and diffusive effects. The cutpoint Stokes number was a linearly decreasing function of fiber Reynolds number. Single fiber efficiencies were calculated from total filter efficiencies and compared to contemporary viscous flow impaction theory (Stechkina et al. 1969), and numerical simulations of single fiber efficiencies from the literature. Existing theories underpredicted measured single fiber efficiencies, although comparison is problematic. The assumption of uniform flow conditions for each successive layer of fibers is questionable; thus, the common exponential relationship between single fiber efficiency and total filter efficiency may not be appropriate in this regime. Copyright © American Association for Aerosol Research.

A short-standoff bistatic lidar system coupled with an aerosol chamber has been built to measure aerosol optical backscatter and laser induced fluorescence cross-sections. Preliminary results show good sensitivity across all channels with high signal-to-noise ratio. © OSA 2012.

Abstract not provided.

Abstract not provided.

Abstract not provided.