Improving the representation of multicomponent aerosols in numerical models

Abstract

This thesis is motivated by the need to improve performance of aerosol simulation in air quality models. I investigate the relationship between multicomponent aerosol sectional and modal distributions, which are the two primary methods used in air quality models. I present a new method for converting multicomponent aerosol distributions from sectional to modal representations with the conservation of both total and component mass. This method can be used to accurately compare distributions with different representations and to enhance the accuracy of hybrid aerosol numerical modules, where both sectional and modal methods are used to represent multicomponent aerosol distribution.

It has been shown that externally mixed particles behave differently in the atmosphere than do internally mixed ones. This thesis introduces a new definition to distinguish external and internal aerosol mixtures with the concept of a mixing criterion. I constructed a new aerosol model incorporating this definition, allowing it to treat aerosol particles as either external or internal mixture. The model includes a newly formulated coagulation process for external mixtures, where the coagulated particles are assigned to corresponding section and distribution based on their composition and size. Based on this model, I investigate the interactions between aerosol mixing state, semivolatile organic partitioning, and coagulation within a simplified urban scenario.