DMCA
Thermodynamic Properties of Multifunctional Oxygenates in Atmospheric Aerosols from Quantum Mechanics and Molecular
BibTeX
@MISC{_thermodynamicproperties,
author = {},
title = {Thermodynamic Properties of Multifunctional Oxygenates in Atmospheric Aerosols from Quantum Mechanics and Molecular},
year = {}
}
Share
 |
 |
 |
 |
||
OpenURL
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 [¢Hvap(Tb)], normal boiling point (Tb), and the change in heat capacity (liquid to gas) of the compound upon phase change [¢Cp(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 that we used in the derived Clausius-Clapeyron equation.
Keyphrases
quantum mechanic thermodynamic property multifunctional oxygenates atmospheric aerosol dicarboxylic acid clausius-clapeyron equation liquid vapor pressure averaged error predicted solid vapor pressure cohesive energy density molecular dynamic generic force field corresponding heat ambient particulate matter molecular model aerosol phase polar multifunctional oxygenates derived clausius-clapeyron equation organic compound heat capacity atomic charge vapor pressure prediction ambient temperature differ phase change cp vapor pressure available literature data linear dependence assumption recent study normal boiling point hvap gas-particle partitioning atmospheric organic compound pure compound molecular simulation atomistic simulation temperature-dependent vapor pressure equation simulation method experimental value
