Chemical Composition and Optical Properties of Laboratory-generated Biomass Burning Organic Aerosols

Description

Biomass burning organic aerosols (BBOA) impact Earth’s climate directly by scattering and absorbing sun light, and indirectly by modifying processes controlling formation of clouds and their lifecycles. This alteration to our planet’s climate is highly influenced by variability in the chemical composition, morphology and mixing states of individual BBOA particles. In this work, four types of biomass fuels were burned in a laboratory combustion chamber to mimic BBOA representative of North American wildfires. BBOA samples were then collected using a cascade impactor for further single-particle chemical imaging. Samples of individual particles were probed using a computer-controlled scanning electron microscope coupled with energy dispersive X-ray microanalysis (CCSEM/EDX), which provided information on the particle-types determined based on the elemental composition and morphology. Complementary synchrotron-based soft X-ray microscopy (STXM/NEXAFS) was utilized to investigate and quantify extents of external and internal mixing. The later technique also provided advanced speciation of carbon bonding within individual particles, allowing to distinguish between organic carbon, elemental carbon (soot), and inorganic components. Parameterized mixing state metrics were then correlated with online optical measurements recorded during each of the individual burning experiments. Results have shown significant differences in the elemental composition and optical properties between different fuels.