Georg Rupprecht

The lifetime of ice particles in the solar system

Abstract A new technique for the measurement of the sublimation rate of individual ice particles is described. With this technique experimental data obtained under simulated space conditions agree with the values computed from scattering theory. It is shown that under solar illumination the sublimation rate of water ice particles is most sensitively influenced by the absorption properties of ice in the near-infrared region. A comparison of experimental results and results calculated with the use of different choices for the complex index of refraction establishes a preference for the published data by J. E. Bertie, H. J. Labbe, and E. Whalley [ J. Chem. Phys . 50, 4501–4520 (1969)]. Using these data the lifetimes of ice particles have been computed as a function of particle radius for solar distances of 0.5, 0.75, and 1.0 AU. If these results are applied to ice particle distributions, the distributions become drastically compressed and a quasi-stable particle radius of the order of 15 μm can be predicted for any solar distance.

Particle Collection Characteristics of a Prototype Electrostatic Precipitator (ESP) for a Differential TEOM System

A differential tapered element oscillating microbalance (TEOM) system that includes an electrostatic precipitator (ESP) that is alternately switched on and off has been developed to improve the measurement of airborne particulate matter mass. Preliminary results showed that it has the potential to overcome the difficulties inherent in PM mass measurement and holds the promise of the measurement of PM mass as it exists in ambient air at ambient temperature. A critical aspect of this device is that the ESP totally removes particles from the air stream. In this study a prototype ESP developed by Rupprecht and Patashnick (R&P) Co., Inc. was evaluated for particulate removal efficiency. Laboratory tests were conducted to determine the removal efficiencies for different-sized particles by generating ultrafine (< 0.1 μ m) and fine (> 0.1 μ m) particles. The ultrafine particles were generated using a 5% solution of sodium chloride, while the fine particles were generated with the different sizes (0.5 μ m and 1 μ m) of polystyrene latex particles. The discrete size intervals of generated ultrafine particles were obtained from an electrical differential mobility analyzer (DMA). The transmitted ultrafine and fine particles passing through the ESP were then detected using a condensation particle counter (CPC) and a LAS-X, respectively. The overall particle collection efficiency of the ESP was calculated from the differential particle collection efficiencies and the specific particle size distributions of the test aerosols. The results showed that the collection efficiencies of the ESP were essentially constant over the range of corona current levels tested, indicating that those were not strong functions of the applied potential if the field strength was sufficiently high.