Seminar: "Investigating Complex Mixtures Using Ultrahigh Resolution Orbitrap Elite Mass Spectrometry: The Molecular Composition of Wildland Fire Aerosol"

Mar 2, 2018
11 a.m.
Brauer Hall, Room 12

Lynn R. Mazzoleni will present.

Abstract: Wildland biomass burning, in the form of wildfires or prescribed burning, is an important emission source of organic aerosol to the atmosphere contributing to climate change, visibility reduction, and adverse human health affects. The molecular chemistry of atmospheric aerosol is important because it can be used to better understand its lifecycle and the physical properties of aerosol in the atmosphere. In this work, we investigated the molecular properties of water-soluble organic carbon (WSOC) for five globally important fuels: Alaskan peat, Russian peat, Florida swamp peat, wildland cheat grass, and Ponderosa pine needles. Aerosol from laboratory controlled combustion experiments was collected on filters and extracted in HPLC grade water.

Ultrahigh resolution mass spectrometry was performed after a 2-step solid-phase extraction procedure using a modified HULIS protocol. Thousands of molecular formulas were assigned to the mass spectra collected after electrospray ionization and atmospheric pressure photoionization. CHO compounds were the most dominant fraction by number, followed by CHNO and CHOS compounds. In all cases, a wide molecular diversity of compounds was eluted in the first elution, while less oxidized and more aromatic molecules with lower average O/C and H/C ratios were eluted with alkaline methanol. We observed Absorption Ångström Exponents (AAE) of 10.4-15.2 for the first elution and 6.7-8.8 for the second elution, indicating clear differences in the absorption properties of WSOC in the two elutions. Overall, most of the assigned molecular formulas demonstrated low O/C ratio (< 1) typical for fresh biomass combustion aerosols. Molecular similarity was observed in all 3 peat burning aerosol samples and the 2 wildland fuel samples (cheat grass and Ponderosa pine needles), however the two types of fuels were considerably different, particularly with respect to the molecular weight range of the species. This is most likely due to the difference in combustion, where peat fuels only smoldered, but cheat grass and pine needles had a flaming period before smoldering.

In this seminar, I will demonstrate the power of ultrahigh resolution mass spectrometry with novel insights on the detailed molecular chemistry of biomass combustion aeros