Size- and Composition-Resolved Externally Mixed Aerosol Model

The need for a numerical algorithm to predict the growth of external mixtures of aerosol populations is common to several current areas of study, including aerosol radiative effects, particle production processes, and pollution source apportionment. This work describes a model that solves this problem for explicit external and internal mixtures for the processes of coagulation, condensation, deposition, activation, and nucleation. The solution is numerically accurate for both particulate mass and number conservation by virtue of a dual-moment sectional method for solute growth. In addition, evaporable components are calculated in moving sections to retain information during particle activation in supersaturated conditions. The model is illustrated by application to the problem of cloud processing in a marine boundary layer capped with a layer of stratus clouds. The aerosol population is tracked in an air parcel circulating within the boundary layer and through the cloud layer. Boundary layer structure and cloud supersaturation profiles are predicted from gradients of observed thermodynamic variables. The model shows the differential growth of particles during cloud processing in two different types of particle populations, one of sea-salt origin and the other of sulfate origin.