AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Quantifying Aerosol Mixing State with Entropy Measures
NICOLE RIEMER, Matthew West, University of Illinois at Urbana-Champaign
Abstract Number: 223 Working Group: Aerosols, Clouds, and Climate
Abstract The “mixing state” of a particle population is the distribution of the per-particle composition. To understand aerosol climate impacts, the mixing state is important because it governs optical properties and cloud condensation nuclei activity, for example. In discussions on mixing state the terms “external mixture” and “internal mixture” are frequently used to describe how different species are distributed over the particle population. In an external mixture the particle species reside in different particles, whereas in an internal mixture the particle species are present within one particle.
While these terms may be appropriate for idealized cases, it has long been realized from observational evidence that ambient aerosol populations rarely fall in these two simple categories. Here we present, for the first time, a metric for aerosol mixing state based on rigorous information-theoretic entropy concepts. This is based on the division of species diversity into average per-particle diversity versus bulk population diversity. We illustrate this new framework with model results from the stochastic particle-resolved model PartMC-MOSAIC. These results demonstrate how the mixing state metrics evolve with time for several archetypal cases, each of which isolates a specific process such as coagulation, emission and condensation. We additionally present an analysis of the mixing state evolution for a complex urban plume case, for which these processes occur simultaneously.