Application of the stochastic particle-resolved model PartMC to chamber experiments

Poster PDF

Description

The stochastic particle-resolved aerosol model PartMC is a recently developed aerosol model that explicitly resolves and tracks the size and composition of individual particles as they undergo transformations by coagulation and condensation in the atmosphere. This approach spreads the initial aerosol size distribution over a finite number of Monte Carlo particles and allows them to evolve using the appropriate probabilities for coagulation and other processes.

For this study we adapted PartMC to represent the aerosol evolution in an aerosol chamber, with the intention to use the model as a tool to interpret and guide chamber experiments in the future. For this purpose we added chamber-specific processes such as wall loss due to particle diffusion and sedimentation and dilution effects due to sampling using the approach by Naumann (2003). We also implemented a treatment of fractal particles based on Naumann (2003) to account for the morphology of agglomerates and its impact on particle dynamics.

Here we show our model validation using experimental data from an aerosol chamber at the Department of Civil and Environmental Engineering at the University of Illinois. We obtained several size distribution data sets from coagulation experiments with ammonium sulfate particles. Moreover, scanning electron microscope (SEM) images of the filters provided evidence that coagulation significantly altered the particle structure from primary spherical particles to fractal-like agglomerates. We developed a fitting optimization approach to determine the best-estimate values for the wall loss parameters based on minimizing the L2-norm of the model errors of number and mass distributions. Obtaining the best fit required taking into account the non-spherical structure of the particles.