AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Effect of Ammonia on the Volatility of Dicarboxylic Acids
ANDREA PACIGA, Ilona Riipinen, Spyros Pandis, Carnegie Mellon University
Abstract Number: 373 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Dicarboxylic acids are major components of ambient organic aerosol in most areas throughout the year. Often the concentrations, of especially the smaller ones in the particulate phase, are a lot higher than what their vapor pressure and the corresponding gas-to-particle equilibrium partitioning would allow. One possible explanation for this preference of the dicarboxylic acids for the particulate phase is the reaction with ammonia and the formation of the corresponding salts. We use using a tandem differential mobility analyzer – thermodenuder system to measure the volatility of a small (ammonium oxalate) and a medium size (ammonium adipate) salt. The evaporation of these dicarboxylates is studied for several particle sizes and two heating residence times. The particles do not reach equilibrium in the thermodenuder and therefore a dynamic mass transfer model is used for the interpretation of the results and the estimation of the saturation vapor pressure and enthalpy of vaporization of the dicarboxylates.
The solid state saturation vapor pressure of ammonium oxalate is estimated to be more than five orders of magnitude lower than that of oxalic acid. Ammonium adipate, however, did not show an appreciable difference in saturation vapor pressure or enthalpy of vaporization when compared to adipic acid. These results suggest that the dominating presence of oxalate in the particulate phase is at least partially due to its ability to form strong-low volatility salts with ammonia in the atmosphere.