A mathematical model of the dynamics of photochemical aerosols should include emissions of primary particulates and gaseous precursors of secondary aerosols, homogeneous nucleation, heterogeneous condensation, heterogeneous chemical reaction, coagulation, advection, diffusion, settling, and deposition on surfaces. This report discusses the theory of each of these processes and assesses the relative importance of each in shaping the volume distribution of photochemical aerosols. The authors conclude that in Los Angeles photochemical smog heterogeneous condensation is the principal mechanism for changes of the volume distribution in the accumulation size range, though homogeneous nucleation can be important under certain conditions for forming very small particles (less than 100 A diameter). Coagulation must be considered in reshaping the size distribution of emissions and in reducing the number of particles formed by homogeneous nucleation. An in-depth assessment is also presented of the pathways for the formation of aerosol material from the gas phase via homogeneous and heterogeneous chemistry. Finally, the equations governing the evolution of the photochemical aerosol are derived and simplified on the basis of order-of-magnitude calculations of the individual terms, and various equations for different properties of the aerosol are derived and discussed.

Includes bibliographical references (p. 230-232). "May 1976." "Project Officer, Kenneth L. Demerjian." References: p. 147-155.