Smoke, Dust, and Haze: Fundamentals of Aerosol Dynamics PDF

PREFACE

The first edition of this book, published in 1977, included an extended discussion of aerosol dynamics, the study of the factors that determine the distribution of aerosol properties with respect to particle size. The distributions change with position and time in both natural and industrial processes. The ability to predict and measure changes in the distribution function are of central importance in many applications from air pollution to the commercial synthesis of powdered materials. The aerosol dynamics approach makes it possible to integrate a broad set of topics in aerosol science usually treated in an unconnected manner. These include stochastic processes, aerosol transport, coagulation, formation of agglomerates, classical nucleation theory, and the synthesis of ultrafine solid particles.

I had started writing the first edition after participating in ACHEX, the first large scale atmospheric aerosol characterization experiment which took place in California in the early seventies. K. T. Whitby had shown the power of the new instruments that had been developed for the rapid determination of particle size distributions including the single particle optical counter and electrical mobility analyzer. I realized that this instrumentation provided enough information to warrant a new treatment of aerosol dynamics linked to improved experimental capabilities. (An earlier ground-breaking book on The Dynamics of Aerocolloidal Systems had been published in 1971 by G. M. Hidy and J. R. Brock.)

In the approach adopted in my first edition, the derivation and use of the general dynamic equation for the particle size distribution played a central role. This special form of a population balance equation incorporated the Smoluchowski theory of coagulation and gas-to-particle conversion through a Liouville term with a set of special growth laws; coagulation and gas-to-particle conversion are processes that take place within an elemental gas volume. Brownian diffusion and external force fields transport particles across the boundaries of the elemental volume. A major limitation on the formulation was the assumption that the particles were liquid droplets that coalesced instantaneously after collision.

In the second edition, I have sharpened the focus on aerosol dynamics. The field has grown rapidly since its original applications to the atmospheric aerosol for which the assumption of particle sphericity is usually adequate, especially for the accumulation mode. Major advances in the eighties and nineties came about when we learned how to deal with (i) the formation of solid primary particles, the smallest individual particles that compose agglomerates and (ii) the formation of agglomerate structures by collisions. These phenomena, which have important industrial applications, are covered in two new chapters. One chapter describes the extension of classical coagulation theory for coalescing particles to fractal-like (power law) agglomerates. The other new chapter includes a discussion of the collision-coalescence mechanism that controls primary particle formation in high temperature processes. This phenomenon, first recognized by G. Ulrich, was later incorporated in the general dynamic equation by W. Koch and myself. Also included is an introduction to the fundamentals of aerosol reactors for the synthesis of submicron solid particles. In aerosol reactor design, I have benefited from the work of S. E. Pratsinis (University of Cincinnati and ETH, Zurich) and his students who have pioneered the industrial applications of aerosol dynamics.

Several other chapters have been substantially rewritten to reflect the sharpened focus on aerosol dynamics. For example, the chapter on optical properties has been expanded to include more applications to poly disperse aerosols. It helps support the chapter that follows on experimental methods in which coverage of instrumentation for rapid size distribution measurements has been augmented. Methods for the rapid on-line measurement of aerosol chemical characteristics are discussed in the chapters on optical properties and experimental methods. This chapter has been strongly influenced by the work of the Minnesota group (B. Y. H. Liu, D. Y. H. Pui, P. McMurry, and their colleagues and students) who continue to invent and perfect advanced aerosol instrumentation. Discussions of the effects of turbulence have been substantially expanded in chapters on coagulation and gas-to-particle conversion.

The chapter on atmospheric aerosols in the first edition has been updated and completely rewritten within an aerosol dynamics framework. This important field has implications for the earth's radiation balance and global climate change. J. H. Seinfeld, R. C. Flagan (Caltech), and other members of the aerosol dynamics community are active in this area.

Theory and related experimental measurements are discussed throughout the text. Microcontamination in the semiconductor industry, visibility degradation, manufacture of pyrogenic silica, filtration, and many other applications are used as illustrative examples. The emphasis is on physical explanations of the phenomena of interest, keeping the mathematical analysis to a relatively simple level. Extensive use is made of scaling concepts, dimensional analysis, and similarity theories. These approaches are natural to aerosol dynamics because of the wide range in particle sizes, going from molecules to the stable nuclei of homogeneous nucleation, to primary nanometer and ultrafine solid particles and their aggregates. In keeping with the sharpened focus on dynamics, the book subtitle has been changed to Fundamentals of Aerosol Dynamics.