Large-scale forest fires significantly contribute to the atmospheric influx of primary organic aerosol (POA) and volatile organic compounds (VOCs). These emissions undergo atmospheric processing to form secondary organic aerosol (SOA). Many studies have investigated the chemical composition of POA, generated through the combustion of various classes/species of biomass. In addition, studies have been conducted on how atmospheric processing of POA impacts its chemical composition and light-absorption properties. Globally, there is an increased frequency of devastating wildfire events that occur at the wildland-urban interface, burning not only biomass materials but also a wide range of ‘urban’ man-made materials. The chemical composition of VOC emissions from fires occurring at the wildland-urban interface is poorly characterized, as are their aged products.<br/>This work compares the chemical composition of laboratory-generated proxies of POA from the pyrolysis and combustion of traditional biomass versus that of common urban materials. Chemical aging by 1) aqueous-phase reactions of transition metals, and 2) solar UV irradiation is explored by a suite of methods. UV-Vis spectroscopy is used to observe the optical properties of fresh and aged POA. Molecular characterization of fresh and aged samples is determined using ultra-high pressure liquid chromatography photodiode array high resolution mass spectrometry (UHPLC-PDA-HRMS). Two complementary ionization techniques, atmospheric pressure photo ionization (APPI) and electrospray ionization (ESI), are utilized to obtain broad coverage of both polar and nonpolar OA components. This work provides important input for source apportionment of POA from wildland-urban interface fires; chemical transformations that occur with aging POA; and understanding the composition of light-absorbing components in OA (i.e., brown carbon) from various combustion sources.

Composition and atmospheric transformations of organic aerosol emitted from biomass and urban material burning

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