Accessing the Low-polar Molecular Composition of Boreal and Arctic Peat Burning Organic Aerosol via Thermal Analysis and Ultrahigh-Resolution Mass Spectrometry: Structural Motifs and Their Formation

Peatland fires emit organic carbon rich particulate matter into the atmosphere. Boreal and Arctic peatlands are becoming more vulnerable to wildfires, resulting in a need for better understanding of the emissions of these special fires. Extractable, non-, and low-polar organic aerosol species emitted from laboratory-based boreal and Arctic peat burning experiments are analyzed by direct-infusion atmospheric pressure photoionization (APPI) ultrahigh-resolution mass spectrometry (UHRMS) and compared to time-resolved APPI UHRMS evolved gas analysis from the thermal analysis of peat under inert nitrogen (pyrolysis) and oxidative atmosphere. The chemical composition is characterized on a molecular level, revealing abundant aromatic compounds that partially contain oxygen, nitrogen or sulfur and are formed at characteristic temperatures. Two main structural motifs are identified: single-core and multicore, and their temperature dependent formation is assigned to the thermal degradation of the lignocellulose building blocks and other parts of peat.