American Association for Aerosol Research - Abstract Submission

AAAR 38th Annual Conference
October 5 - October 9, 2020

Virtual Conference

Abstract View


Organic Tracers of Low and High Molecular Weight in Particulate Matter with Thermal Desorption -- Pyrolysis -- Gas Chromatography/Mass Spectrometry

ALENA KUBATOVA, Brett Nespor, Richard Cochran, Haewoo Jeong, Frank Bowman, David Delene, Evguenii I. Kozliak, Bin Yao, University of North Dakota

     Abstract Number: 584
     Working Group: Carbonaceous Aerosol

Abstract
Particulate matter (PM) consisting of both organic carbon (OC) and elemental carbon (EC) causes a wide range of effects in the atmosphere, yet only a fraction of OC is fully characterized. Typically thermal optical analysis (TOA) is employed to determine the OC and EC distribution. Further chemical speciation for source apportionment of OC compounds is typically accomplished with either thermal desorption (TD) or solvent extraction followed by GC-MS. Nevertheless, these current methods tend to favor the detection of low molecular weight, semi-volatile compounds and may discriminate against higher molecular weight species.

In this study, we investigate TOA in comparison to TD-pyr-GC-MS to identify various organic compounds for samples obtained at rural North Dakota and during the CARES campaign. The combination of TOA quantitative data with the qualitative characterization of the semi-volatile fraction (TD) was complemented with structural information on larger molecular weight species using stepwise pyrolysis (pyr), which enabled improved insight on characterization of OC and its high molecular weight fraction. TD (300 °C) and pyr (˃ 500 °C) GC-MS data provided specific homology profiles for alkanes, alkenes, polycyclic aromatic hydrocarbons (PAHs) and a variety of other organic compounds, where TD was mostly associated with biogenic origin. In the pyr fractions of carbonaceous PM, highly abundant homologous series of n-alkenes, n-alkylbenzenes, PAHs, n-alkanes, and substituted phenols were observed. The occurrence of these compounds based on newly developed pyrolytic indicators reflects the breakdown of biogenic sources, e.g., plant lipids, although certain sampling periods showed a contribution of anthropogenic origin.