The complex composition of organic aerosols emitted during burning varies between Arctic and boreal peat

Abstract

Peatlands in the northern hemisphere are a major carbon storage but face an increased risk of wildfires due to climate change leading to large-scale smoldering fires in boreal and Arctic peatlands. Smoldering fires release organic carbon rich particulate matter, which influences the earth’s radiative balance and can cause adverse health effects for humans. Here we characterize the molecular composition of biomass burning particulate matter generated by laboratory burning experiments of peat by electrospray ionization 21 T Fourier-transform ion cyclotron resonance mass spectrometry, revealing a highly complex mixture of aromatic and aliphatic organic compounds with abundant heteroatoms including oxygen, sulfur and up to five nitrogen atoms. Primary organosulfur species are identified in the emissions of peat-smoldering, in part also containing nitrogen. Differences are observed when comparing structural motifs as well as the chemical composition of boreal and Arctic peat burning emissions, with the latter containing compounds with more nitrogen and sulfur.

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

“…Additionally, the ionization by APPI is very sensitive for sulfur-containing species, which may result in an overrepresentation of these species . The herein discussed results are in line with our previous study that revealed an unusually high abundance of sulfur-containing species (CHOS, CHNOS) in the polar fraction of the same peat combustion emission extracts …”

“…However, in general, all four peat combustion extracts are vastly similar, regarding both the detected elemental compositions (70–87% common compounds, Figure S1) as well as their intensity distribution in the mass spectra (Figure S2), even though APPI is reported to be less prone to matrix effects . This result contrasts with observations made for the polar organic fraction of these aerosol extracts investigated in a previous study by ESI 21 T FT-ICR MS that revealed distinct differences between the boreal and the Arctic peat-burning aerosols in all compound classes . With regard to Figure , the CHO class is the most abundant compound class (approximately 50–54% int.)…”

“…A detailed description of the peat sampling sites and the laboratory burning experimental set up was given in a previous publication . Briefly, 30 cm deep peat samples (top layer) were collected at four locations in northern Europe.…”

“…Moreover, selective ionization techniques, e.g., electrospray ionization (ESI) targeting polar compounds and atmospheric pressure photoionization (APPI) targeting non/low-polar species, can be utilized to address a specific compositional space . With respect to the unique composition and burning conditions of boreal and Arctic peats compared to other wildfire fuel types, FT-ICR MS has shown an extreme molecular complexity including polar nitrogen- and sulfur-rich OA compounds that were found to be clearly different comparing boreal and Arctic peat. − …”

“…The single-core motif is comprised of larger condensed aromatic ring structures with alkylation, whereas the multicore motif is characterized by smaller interconnected aromatic ring structures . This concept was initially applied to asphaltenes in petroleum but later transferred to OA from brown coal and biomass burning. , For OA, single-core structures are built up during combustion from smaller aromatic structures or humic substances formed by microbial degradation of biomass during peat maturation. , Multicore motifs are derived from lignin structures, soil organic matter biodegradation products (humic substances), or their incomplete thermal degradation …”