Chemical Characterization of Organic Aerosol Tracers Derived from Burning Biomass Indigenous to Sub-Saharan Africa: Fresh Emissions versus Photochemical Aging

Abstract

Wildfires are increasingly frequent and intense, leading to substantial production of biomass burning (BB)-derived organic aerosol (BBOA). BBOA adversely affects public health and perturbs the climate. Although African fires account for over 50% of worldwide BB-derived organic emissions, few studies have systematically analyzed molecular tracers of BBOA in fresh versus photochemically aged BB emissions representative of African fires. Therefore, by using gas chromatography interfaced to electron ionization quadrupole mass spectrometry (GC/EI-MS), we chemically characterized aerosol filter samples collected from both fresh and photochemically aged BB emissions of six biomass fuels found in Sub-Saharan Africa (Cordia africana, Baikiaea plurijuga, Acacia erioloba, Colophospermum mopane, cow dung, and a fuel mixture). BB emissions were generated from a furnace mimicking smoldering combustion and subsequently injected into a humidified laboratory chamber (70% ± 3% RH). Seventeen known BBOA tracer compounds (e.g., levoglucosan, mannosan, coniferyl alcohol, catechol, and palmitic acid) were targeted, quantified, and compared between fresh and photochemically aged BB emissions. Furthermore, total-suspended atmospheric particulate matter (PM) samples collected from Botswana during the fire season were also analyzed by GC/EI-MS. We identified laboratory-generated BBOA constituents that were also found in Botswana PM that could plausibly serve as unique tracers (e.g., D-pinitol) for African BBOA during future field studies.