Showing papers by "George Biskos published in 2005"

Phase Transitions of Single Salt Particles Studied Using a Transmission Electron Microscope with an Environmental Cell

Abstract: The hygroscopic behavior of 0.1 to 4 μ m NaBr, CsCl, NaCl, (NH4)2SO4, and KBr particles were monitored using a transmission electron microscope (TEM) equipped with an environmental cell into which gases can be introduced. This instrument, commonly called an environmental transmission electron microscope or ETEM, allowed us to observe phase transitions and behavior of small particles at relative humidities between 0 and 100%. We used deliquescence relative humidity and efflorescence relative humidity values from the literature for each salt to calibrate the relative humidity in the environmental cell. Using our methodology, we reliably and accurately measured the phase transitions and hygroscopic behavior of inorganic particles with the ETEM.

Ozonolysis of Mixed Oleic-Acid/Stearic-Acid Particles: Reaction Kinetics and Chemical Morphology

Abstract: The ozonolysis of mixed oleic-acid/stearic-acid (OL/SA) aerosol particles from 0/100 to 100/0 wt % composition is studied. The magnitude of the divergence of the particle beam inside an aerosol mass spectrometer shows that, in the concentration range 100/0 to 60/40, the mixed OL/SA particles are liquid prior to reaction. Upon ozonolysis, particles having compositions of 75/25 and 60/40 change shape, indicating that they have solidified during reaction. Transmission electron micrographs show that SA(s) forms needles. For particles having compositions of 75/25, 60/40, and greater SA content, the reaction kinetics exhibit an initial fast decay of OL for low O3 exposure with no further loss of OL at higher O3 exposures. For compositions from 50/50 to 10/90, the residual OL concentration remains at 28 ± 2% of its initial value. The initial reactive uptake coefficient for O3, as determined by OL loss, decreases linearly from 1.25 (±0.2) × 10-3 to 0.60 (±0.15) × 10-3 for composition changes of 100/0 to 60/40. At...

Description and Theoretical Analysis of a Differential Mobility Spectrometer

Abstract: Electrical mobility analysis is the most efficient technique for measuring aerosol particle size distributions in the submicron size range. Recent advances in aerosol science underline the need of fast measurements of particle size spectra in this range, and therefore a great amount of effort has been focused towards this direction. This paper provides the description and a theoretical framework for the analysis of a fast-response differerntial mobility spectrometer (DMS). In common with other instruments of its category, it consists of a particle charger, a classification column, and a series of detectors. Passing the sample flow first through a corona-wire diffusion charger that sets a charge on the particles, the aerosol is introduced around the central rod of an inside-out cylindrical classifier equipped with a series of isolated electrode rings connected to sensitive electrometers. Current readings produced by deposition of the charged particles on the electrometer rings are then translated to partic...