AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Molecular Dynamics Simulations of the Mass Accommodation of Dicarboxylic Acids and Other Organic Compounds
Jan Julin, ILONA RIIPINEN, Stockholm University
Abstract Number: 621 Working Group: Aerosol Physics
Abstract The condensational growth of atmospheric aerosol particles is limited by their ability to accommodate incoming molecules of the various condensing vapor species. This ability is quantified by the mass accommodation coefficient, which gives the fraction of incoming molecules that will remain in the condensed phase. Molecular dynamics (MD) simulations provide a straightforward method to determine the mass accommodation coefficient, since in MD the trajectories of individual molecules can be followed as a function of time.
We will present MD mass accommodation simulation results of several organic species on surfaces consisting of the same species as the incoming vapor molecule. The species studied include two dicarboxylic acids, namely adipic and succinic acid, and a simple polycyclic aromatic hydrocarbon, naphthalene. The interaction potential used was the OPLS-AA force field, and the simulations were performed at a constant temperature of T=313.15 K. The studied surfaces include both planar surfaces and nanosized droplets. As the simulation temperature is below the melting points of the studied species, we also studied separately cases where the condensed phase was either a subcooled liquid or a solid.
The following simulation setup was used: at the beginning of a simulation an incoming molecule is generated at roughly 2 nm above the target surface, and the simulation is then run for 80 ps. By simulating one hundred of such incoming molecules for each studied surface, the value of the mass accommodation coefficient can be determined by studying the fates of the incoming molecules at the surface. The simulations resulted in mass accommodation coefficients close to unity.