George Biskos

Bio: George Biskos is an academic researcher from The Cyprus Institute. The author has contributed to research in topics: Aerosol & Particle. The author has an hindex of 29, co-authored 104 publications receiving 3156 citations. Previous affiliations of George Biskos include Delft University of Technology & Harvard University.

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...

Nanosize effect on the hygroscopic growth factor of aerosol particles

Abstract: [1] The hygroscopic growth factors of NaCl particles having dry mobility diameters of 6 to 60 nm were measured using a tandem nano-Differential Mobility Analyzer. The growth factors steadily decreased within detection limit for dry sizes below 40 nm. The decrease is quantitatively predicted by a model that includes the Kelvin effect and a size-dependent shape factor. This factor is not tuned to the data but rather is grounded in theoretical predictions from literature. Agreement in growth factors for particles generated by two independent methods (namely, vaporization-condensation and electrospray), as well as observations of prompt deliquescence, indicates the absence of significant chemical impurities.

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Abstract: Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Introduction to the Finite Element Method

Abstract: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Chemical and microphysical characterization of ambient aerosols with the aerodyne aerosol mass spectrometer

Abstract: The application of mass spectrometric techniques to the realtime measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between similar to 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li(+) ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described. (c) 2007 Wiley Periodicals, Inc.