Molecular dynamic simulation of dicarboxylic acid coated aqueous aerosol: structure and processing of water vapor.

Organic monolayers at the surfaces of aqueous aerosols play an important role in determining the mass, heat transfer rate and surface reactivity of atmospheric aerosols. They can potentially contribute to the formation of cloud condensation nuclei (CCN) and are involved in a series of chemical reactions occurring in atmosphere. Recent studies even suggest that organic-coated interfaces could have played some role in prebiotic biochemistry and the origin of life. However, creating reproducible, well-characterized aqueous aerosol particles coated with organic films is an experimental challenge. This opens the opportunity for computer simulations and modeling of these complex structures. In this work, molecular dynamics simulation was 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 were chosen to coat a water droplet consisting of 2440 water molecules. For malonic acid coated aerosol, the surface acid molecules dissolved into the water core and formed an ordered structure due to the hydrophobic interactions. The acid and the water are separated inside the aerosol. For other nanoaerosols coated with low solubility acids, phase separation between water and acid molecules was observed on the surface of the particle. To study the water processing of the coated aerosols, the water vapor accommodation factors were calculated.