Tutorial 2:

Introduction to Aerosols. II.

Richard Flagan, California Institute of Technology, USA

Abstract: This tutorial continues the basic introduction to aerosol science, continuing the discussion of the physics of a single particle, and then examining particle diffusion, and finally turning our attention to the dynamics of aerosol populations.  While large particles can be separated due to their inertia, inertial methods are difficult to use for small ones, but aerodynamic drag can be used for small particles if they are first charged and then subjected to an electric field.  This method is applied in differential mobility analysis to obtain the particle size distribution in terms of a mobility equivalent diameter in the scanning mobility particle sizer (SMPS).  Small particles can also deviate from the gas motion because Brownian motion causes them to diffuse, enhancing deposition of small particles in the respiratory tract, sampling systems, and filters.  Diffusion also degrades the performance of the SMPS for small particles, which will be discussed.  Aerosol particles can change size due to diffusion of vapors to or from them.  Vapors can alter the particles and their size distribution by condensing on them or evaporating from them.  We will examine the thermodynamics and vapor transport processes, their use in aerosol particle counting in the condensation particle counter (CPC), and examine effects on the particle size distribution.  Under extreme conditions, vapors form new particles directly from the vapor phase through homogeneous nucleation of one or more vapor species, which we shall briefly examine.  The particle size distribution is also altered by coagulation in which two particles combine through collision to form one large particle. These diverse processes can be combined to form a general dynamic equation for aerosols, which will be the final topic of these introductory aerosols.

Short bio: Richard C. Flagan is the McCollum/Corcoran Professor of Chemical Engineering and Environmental Science and Engineering at the California Institute of Technology.  He has served as the President of AAAR, and as Editor-in-Chief of Aerosol Science and Technology.  His research spans the field of aerosol science, including atmospheric aerosols, aerosol instrumentation, homogeneous nucleation, aerosol synthesis of nanoparticles and other materials, bioaerosols ranging from pollen to the SARS-CoV-2 virus, and aerosols in the atmospheres of other worlds.  His many contributions to the field of aerosol science have been acknowledged with the Sinclair Award of the AAAR, the Smoluchowski Award of the Gesellschäft für Aerosolforschung, and the Fuchs Award.  He is a member of the National Academy of Engineering.