Bivariate population dynamics simulation of fractal aerosol aggregate coagulation and restructuring

In the present work a previously developed model of fractal aggregates evolution from an initial morphology (as described by their fractal dimension) towards to that defined by the prevailing coagulation mechanism is extended in two directions. Firstly a new constitutive law for the fractal dimension of the aggregate resulting from a coagulation event is generalized and secondly a restructuring mechanism is added to the population balance model. Several techniques from detailed Monte Carlo simulations to simple monodisperse (in both volume and fractal dimension) approximations are employed for the solution of the corresponding bivariate coagulation equation. The parametric evolution of the fractal dimension of aggregates for the case of Brownian coagulation in the continuum regime is studied and the results indicate that the existence of restructuring makes the evolution dynamics of the fractal dimension distribution of the aggregate population much richer than in the case of simple coagulation examined previously. As an application of the present approach, the morphological data of Xiong and Friedlander [(2001) Morphological properties of atmospheric aerosol aggregates. Proceedings of the National Academy of Sciences of USA, 98, 11851–11856] on atmospheric aggregates are examined and are shown to be consistent with a combined coagulation–restructuring process.