| Title: | Thermodynamic properties of multifunctional oxygenates in atmospheric aerosols from quantum mechanics and molecular dynamics: dicarboxylic acids |
| Author(s): | Tong C; Blanco M; Goddard WA; Seinfeld JH; |
| Address: | "Department of Environmental Science and Engineering, Material and Process Simulation Center, California Institute of Technology, Pasadena, California 91125, USA" |
| ISSN/ISBN: | 0013-936X (Print) 0013-936X (Linking) |
| Abstract: | "Ambient particulate matter contains polar multifunctional oxygenates that partition between the vapor and aerosol phases. Vapor pressure predictions are required to determine the gas-particle partitioning of such organic compounds. We present here a method based on atomistic simulations combined with the Clausius-Clapeyron equation to predict the liquid vapor pressure, enthalpies of vaporization, and heats of sublimation of atmospheric organic compounds. The resulting temperature-dependent vapor pressure equation is a function of the heat of vaporization at the normal boiling point [deltaHvap(Tb)], normal boiling point (Tb), and the change in heat capacity (liquid to gas) of the compound upon phase change [deltaCp(Tb)]. We show that heats of vaporization can be estimated from calculated cohesive energy densities (CED) of the pure compound obtained from multiple sampling molecular dynamics. The simulation method (CED) uses a generic force field (Dreiding) and molecular models with atomic charges determined from quantum mechanics. The heats of vaporization of five dicarboxylic acids [malonic (C3), succinic (C4), glutaric (C5), adipic (C6), and pimelic (C7)] are calculated at 500 K. Results are in agreement with experimental values with an averaged error of about 4%. The corresponding heats of sublimation at 298 K are also predicted using molecular simulations. Vapor pressures of the five dicarboxylic acids are also predicted using the derived Clausius-Clapeyron equation. Predicted liquid vapor pressures agree well with available literature data with an averaged error of 29%, while the predicted solid vapor pressures at ambient temperature differ considerably from a recent study by Bilde et al. (Environ. Sci. Technol. 2003, 37, 1371-1378) (an average of 70%). The difference is attributed to the linear dependence assumption thatwe used in the derived Clausius-Clapeyron equation" |
| Keywords: | "Aerosols Air Pollutants/*analysis/chemistry Air Pressure Dicarboxylic Acids/*analysis/chemistry Hydrogen Bonding Models, Chemical Predictive Value of Tests Quantum Theory Thermodynamics Volatilization;" |
| Notes: | "MedlineTong, Chinghang Blanco, Mario Goddard, William A 3rd Seinfeld, John H eng Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, Non-P.H.S. 2004/08/10 Environ Sci Technol. 2004 Jul 15; 38(14):3941-9. doi: 10.1021/es0354216" |
