10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Introduction to Aerosols Tutorials
RICHARD FLAGAN, California Institute of Technology
Abstract Number: 1388 Working Group: Aerosol Education
Abstract A set of two Introduction to Aerosols Tutorials has been presented for many years at AAAR. This paper will give a brief overview.
Tutorial 1 is the first of two that introduce the broad field of aerosol science. We begin with the behavior of individual particles to understand how they behave in the environment, and the physical principles on which most aerosol measurements are based. The drag forces that act on a particle determine its settling velocity and whether it is able to follow the flow of a gas. Several different models describe the drag forces: Stokes law applies for spherical particles moving at modest velocities, though a slip correction must be introduced to account for noncontinuum effects for particles small compared to the mean-free-path of the gas molecules. Other corrections are required if the velocity becomes large enough the fluid inertia affects the motion. Knowledge of these scaling principles makes it possible to relate particle behavior in seemingly disparate systems, and make it possible to determine particle size. The drag forces also determine Brownian motion, and, hence, affect their deposition and losses in the respiratory tract, in sampling systems, and in filters, causing aerosol filtration to be more effective than filtration of particles from liquid media. We will briefly look at how this aerodynamic behavior is employed in determining particle size in a wide range of instruments, including the migration of charged particles in mobility analyzers.
Tutorial 2 continues the basic introduction to aerosol science. In this session we focus on developing the tools to describe the dynamics of aerosol populations. An aerosol is an ensemble of particles in a gas, and the particles are distributed over a range of sizes. Therefore, they must be represented by a particle size distribution. We will discuss the representation of aerosol populations as size distributions, their graphical representation, and models such as the log normal-distribution. Condensation and evaporation of volatile species onto particles determines their growth in the atmosphere, and efficient counting of particles too small to detect optically in condensation particle counters. Both continuum and noncontinuum effects must again be considered, as must the surface tension which governs particle activation, initial activation, and the possibility of nucleating new particles from the vapor phase. These processes also alter the shape of the size distribution. Particle-particle collisions lead to coagulation, which further alters the size distribution. We will examine how these diverse processes are combined to describe the population dynamics for aerosol systems.