AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Thermal Decomposition of Organic Species from Biogenic Secondary Organic Aerosol in Thermal Desorption Instruments
HARALD STARK, Laxmi Narasimha Yatavelli, Samantha Thompson, Jordan Krechmer, Joel Kimmel, Brett Palm, Weiwei Hu, Patrick Hayes, Douglas Day, Pedro Campuzano-Jost, Manjula Canagaratna, John Jayne, Douglas Worsnop, Jose-Luis Jimenez, CIRES, University of Colorado
Abstract Number: 170 Working Group: Aerosol Chemistry
Abstract The chemical composition of secondary organic aerosol (SOA) is crucial to the understanding of the formation and processing of this important particle class. Between 1,000 and 10,000 different molecules can be found in a typical aerosol sample from biogenic origin. Identification of these molecules and estimation of their volatilities is important to quantify the total amount of SOA produced.
We will present results from a high-resolution chemical ionization time-of-flight mass spectrometer (HRToF-CIMS), operated with two different thermal desorption inlets designed to characterize the aerosol as well as the gas phase chemical composition. We used a micro-orifice volatilization impactor (MOVI) and a filter inlet for gases and aerosols (FIGAERO). The data were collected during two field campaigns, BEACHON-RoMBAS in a Ponderosa pine forest in Colorado in the summer of 2011 and SOAS in a mixed forest in Alabama in the summer of 2013.
Volatility distributions derived from the signal vs. temperature profiles (thermograms) show much lower volatilities than those estimated from a functional group contribution method (SIMPOL) based on the detected molecular formulas. We interpret those differences as being due to large fractions of the compounds present in aerosols undergoing thermal decomposition upon heating in the instruments. The estimated impacts on volatility of different possible decomposition processes such as decarboxylation, dehydration or fragmentation are examined. We show that the results from the thermogram method are consistent with those obtained using thermal denuders combined with high-resolution aerosol mass spectrometer (AMS) data. Our findings indicate that many commonly used thermal desorption methods might lead to inaccurate results in terms of the identification of molecules present in SOA. Further, the onset of thermal decomposition at moderate temperatures might have implications for the thermal stability of the aerosols and could also give insights into the chemical processes occurring inside the particles.