Determination of saturation pressure and enthalpy of vaporization of semi-volatile aerosols: The integrated volume method

Abstract

This study presents the integrated volume method for estimating saturation pressure and enthalpy of vaporization of a whole aerosol distribution. We measure the change of total volume of an aerosol distribution between a reference state and several heated states, with the heating performed in a thermodenuder. In both the reference and heated states, the aerosol should be at equilibrium: that is, the surrounding gas phase should be saturated with the vapor of the aerosol species. We derive an expression that correlates the volume change to the inverse of temperature from which the saturation pressure and enthalpy of vaporization can be estimated. Transport and aerosol dynamics computational models are developed to investigate the two conditions for this analysis to be valid: (1) the aerosol should be at equilibrium at the exit of the thermodenuder and (2) there should be no re-condensation or further evaporation downstream of the thermodenuder. The method is validated with lab generated adipic acid and pimelic acid aerosol. We obtained saturation pressure at 298 K and enthalpy of vaporization of 3.4 × 10 - 5 ( ± 1.2 × 10 - 5 ) Pa and 135 ( ± 13 ) kJ / mol for adipic acid, and 7.2 × 10 - 5 ( ± 1.7 × 10 - 5 ) Pa and 149 ( ± 10 ) kJ / mol for pimelic acid, which are in good agreement with the values reported in the literature.