Abstract View
Volatility Measurement of Organic Aerosol by Mass Fraction Remaining: Challenges and Advances
KAROLINA CYSNEIROS DE CARVALHO, Sohyeon Jeon, Christopher Oxford, Michael Walker, Brent Williams, Washington University in St. Louis
Abstract Number: 380
Working Group: Instrumentation and Methods
Abstract
Organic matter contributes significantly to atmospheric aerosol, constituting a major fraction of submicron particulate matter. A crucial factor that controls the partitioning of the organic constituents of aerosols between the gaseous and condensed phases is their vapor pressure. This dynamic equilibrium influences the rate of reactions in the atmosphere and the fate of the corresponding compounds. Therefore, to be able to address their effects on Earth’s energy balance as well as on human health, accurate measurement of organic aerosol volatility is imperative.
Thermodenuders have been widely used in efforts to quantify the volatility of organic species. They consist of a heated tube in which the aerosol is evaporated and a denuder section to avoid re-condensation by removing the gas phase material. By exposing aerosols to different temperatures, it is possible to generate a mass fraction remaining curve (thermogram) using either a Volatility Tandem Differential Mobility Analyzer (V-TDMA) or an Aerosol Mass Spectrometer (AMS). However, determining volatility variables from AMS derived thermograms remains challenging. Volatility determination requires simultaneous computation of many parameters, including the mass accommodation coefficient, which is usually not known and often assumed to be unity for organic compounds.
Model predictions tend to yield steeper thermograms (i.e. higher volatility) in comparison to experimental data, and the uncertainty in the value of the mass accommodation coefficient has been suggested to play a role in the observed discrepancies. In this work, we studied the evaporation of azelaic acid by generating thermograms using both an AMS and a V-TDMA. Applying a new V-TDMA model, which takes into consideration the charging efficiency and the presence of multiple charges in the aerosol population, we compare the resulting curves from both instruments and discuss the role of the unity mass accommodation coefficient assumption in the calculations of organic aerosol volatility.