Molecular Dynamic Simulation of Dicarboxylic Acid Coated Aqueous Aerosol: Structure and Processing of Water Vapor

XIAOFEI MA (1), Purnendu Chakraborty (1), Brian J. Henz (2), Michael R. Zachariah (1)

(1) University of Maryland-College Park, (2) US Army Research Laboratory, Aberdeen

     Abstract Number: 325
     Last modified: May 7, 2010

Abstract
Low molecular weight dicarboxylic acids constitute a significant fraction of water-soluble organic aerosols in the atmosphere. They have a potential contribution to the formation of cloud condensation nuclei (CCN) and also are involved in a series of chemical reactions occurring in atmosphere.
In this work, molecular dynamics simulations were used to probe the structure and the interfacial properties of the dicarboxylic acid coated aqueous aerosol. Low molecular weight dicarboxylic acids of various chain lengths and water solubility (from malonic acid to azelaic acid) were chosen to coat a water droplet consisting of 2440 water molecules. The starting point of the coated aerosol is an inverted micelle model. Radial density and radial distribution functions were then obtained and the structure evolutions of the coated aerosols were monitored. For malonic acid coated aerosol, after equilibration, the original surface acid molecules dissolved into the water core and form an ordered structure due to the hydrophobic interactions. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed. To study the water processing of the coated aerosol, the water vapor accommodation factors for the coated aerosols were calculated.