Effect of Aerosol Generation Method on Measured Saturation Pressure and Enthalpy of Vaporization for Dicarboxylic Acid Aerosols
Abstract:To date, most studies of the thermodynamic properties of organic aerosols have utilized test aerosols generated by spray atomization followed by a diffusion drying step. Some evidence points to possible biases in measured thermodynamic properties stemming from the presence of residual solvent (water or alcohol) in the dried aerosol. In the current study we compared measurements of thermodynamic properties of organic aerosols generated by atomization of aqueous solutions to those generated by homogeneous condensation using a modified Sinclair-La Mer generator. In particular, using the Integrated Volume Method (Saleh et al. 2008), we measured and compared the saturation pressure (Psat) at 298 K and enthalpy of vaporization (ΔH) of C-6 (adipic) and C-9 (azelaic) dicarboxylic acid aerosol generated using these techniques. We found that Psat and ΔH exhibited no statistically significant difference across the tested aerosol generation methods, indicating that any residual solvent carried by the particles had no impact on the measurements. For adipic acid, we obtained Psat of 3.3 × 10-5 (±0.9 × 10-5) Pa and ΔH of 132 (±8) kJ/mol with atomization, and Psat of 4.2 × 10- 5 (±2.2 × 10-5) Pa and ΔH of 126 (±21) kJ/mol with homogeneous condensation; for azelaic acid, we obtained Psat of 1.4 × 10-5 (±0.5 × 10-5) Pa and ΔH of 145 (±15) kJ/mol with atomization, and Psat of 0.9 × 10- 5 (±0.3 × 10- 5) Pa and ΔH of 158 (±17) kJ/mol with homogeneous condensation. In addition, SEM images of the acids generated by the two methods showed no obvious difference in surface morphology.
Document Type: Research Article
Affiliations: 1: Department of Civil and Environmental Engineering, Duke University, Durham, North Carolina, USA 2: Aerosol Res. Laboratory, Department of Mechanical Engineering, American University of Beirut, Beirut, Lebanon
Publication date: 2010-04-01