AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Estimating Vapor Wall-Loss to Improve Organic Aerosol Volatility Distributions
KERRIGAN CAIN, Eleni Karnezi, Spyros Pandis, Carnegie Mellon University
Abstract Number: 367 Working Group: Aerosol Chemistry
Abstract Vapor wall-loss has been shown to be an important process in smog chamber studies, especially in yield experiments where organic aerosol (OA) concentrations can be underestimated due to semi-volatile vapor losses to chamber walls. Vapor wall-losses are also important, but largely unaccounted for, in active dilution experiments because an evaporating particle-phase component may never be able to fully reach equilibrium if the corresponding vapor-phase component is continually lost to the chamber walls. This study presents results that account for vapor wall-losses in a dilution chamber and estimate volatility distributions of secondary OA (SOA) generated from the ozonolysis of α-pinene and cyclohexene during experiments combining thermodenuder (TD) and isothermal dilution measurements.
In this study, SOA was generated in a main chamber and characterized with a TD. The SOA was also isothermally diluted in a smaller dilution chamber. After correction for particle wall-losses, we generated thermograms and areograms, particle mass fraction remaining as a function of TD temperature or time in the dilution chamber. We then used a dynamic mass transfer model coupled with an error minimization approach to estimate the SOA volatility distributions. However, the model was updated in this work to account for and estimate vapor wall-losses occurring in the dilution chamber. The model results indicated that the bulk vapor wall-loss constant for this chamber and the SOA species studied was ~0.3 h-1 and, when compared to model results that did not account for vapor wall-losses, significantly reduced the uncertainty in the volatility distributions and corresponding properties. In addition, the model predicted that some semi-volatile compounds can completely evaporate from the particle-phase due to vapor wall-losses. This work signifies the importance of accounting for vapor wall-losses to accurately estimate OA volatility.