Determination of Organic Tracers in Atmospheric Particulate Matter Using Thermal Desorption - Pyrolysis with Gas Chromatography

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

     Abstract Number: 571
     Working Group: Carbonaceous Aerosols

Abstract
The chemical composition of organic atmospheric particulate matter (PM) is still a riddle. A variety of methods were developed to determine various organic species, typically involving chromatography with mass spectrometry, yet the limitation of these methods is focus on volatile and extractable constituents. Thermal desorption (TD) methods have been shown to be an effective replacement for the solvent extractions, providing a rich portfolio of tracer species yet representing only volatile organic PM fraction. Although the value of pyrolysis (Pyr) for analysis has been shown, much less is known about PM-related pyrolytic product tracers. Such high molecular weight tracers may include species derived from microplastics (e.g., styrene from polystyrene) or wood burning (e.g., lignin from lignocellulosic biomass) or traces from pollen rupture and biomass abrasion.

We have employed TD-Pyr with gas chromatography-mass spectrometry that enabled the characterization of both volatile and nonvolatile atmospheric markers focusing on agriculturally active North Dakota. Based on the composition of TD fractions evolving below 400 °C, harvesting activities appeared to be related to an increased abundance of longer chain alkanes (waxes). The TD fractions also contained biogenic fatty acids and their methyl esters, along with other biogenic OC tracers including levoglucosan and 6,10,14-trimethyl-2-pentadecanone. By contrast, pyrolytic fractions have shown long homologous series of n-alkenes, n-alkylbenzenes, PAHs, n-alkanes, and substituted phenols, which were further differentiated by Pyr temperature. We were able to interpret and ascribe the observed hydrocarbon profiles to lipid pyrolysis. Novel pyrolytic indicators were developed reflecting the breakdown of biogenic plant lipids, providing a more representative and comprehensive characterization of PM. According to these new indicators, the biogenic portion of PM in North Dakota appeared to be most abundant, although some sampling periods showed anthropogenic contributions.