Understanding Aerosol Chemistry Through Computational Modeling

Abstract

Aerosols are heterogeneous mixtures of solid particles or droplets of liquid in a gas. Atmospheric aerosols originate from vehicle and factory pollution as well as dust, and the particles as well as their reaction products have significant effects on climate, health, and stability of ecosystems. æThus, it is crucial to further understand the chemistry of aerosol formation and aerosol interaction with other molecules, but these complex reactions may include hundreds or thousands of different chemical species. Because it is difficult and error-prone to calculate all the kinetic and thermodynamic properties by hand, we study the reactions computationally using the Reaction Mechanism Generator (RMG). RMG, developed at MIT, is an open-source software tool for automatic generation of kinetic models for large reaction networks. The goal of this project is to add aerosol-relevant functionalities to RMG, which currently works best for gas phase combustion of hydrocarbons. We are working to introduce corrections for liquid phase reactions to account for solubilties of species in liquid droplets. Partition coefficients between solute and solvent are calculated using Linear Solvation Energy Relationships (LSERs), and solute descriptors are determined using a group additivity method. The partition coefficients can then be used to calculate enthalpy, entropy and GibbsÍ free energy of solvation for all species, which will be compared to known thermodynamic parameters for molecules in a database. Further work includes adding additional elements to RMG that are important in atmospheric chemistry, including nitrogen and the halogens, and adding lower temperature rates to RMGÍs database.