Molecular Characterization\nand Photoreactivity of\nOrganic Aerosols Formed from Pyrolysis of Urban Materials during Fires\nat the Wildland–Urban Interface

Fires at the wildland–urban interface (WUI) are\nincreasing\nin magnitude and frequency, emitting organic aerosol (OA) with unknown\ncomposition and atmospheric impacts. In this study, we investigated\nthe chemical composition of OA produced through the 600 °C pyrolysis\nof ten urban materials in nitrogen, which were subsequently aged under\nUV light for 2 h. The analysis utilized ultrahigh-performance liquid\nchromatography (UHPLC) separation, coupled with a photodiode array\n(PDA) detector and a high-resolution mass spectrometer (HRMS) for\nmolecular characterization. Hierarchical clustering analysis demonstrated\nthat lumber-derived OA was the most diverse and distinct in composition.\nUnaged and aged OA (for each urban material) did not significantly\ndiffer in chemical identities. Potential aromatic brown carbon (BrC)\nchromophores (based on their degree of unsaturation) constituted 13–42%\nof all assigned compounds. PDA chromatograms revealed multiple BrC\nchromophoric species that were either enhanced or degraded as a result\nof UV aging, providing insights into specific BrC chromophores responsible\nfor photobleaching and photoenhancement of the overall absorption\ncoefficient. Thirty-six BrC chromophores were identified across the\nten OA types, and their structures were confirmed using reference\nstandards. Components of plasticizers and resins, such as phthalic\nand terephthalic acids, were structurally confirmed in the samples.\nWe present potential species for WUI fires as components of resins,\nepoxies, dyes, and adhesives commonly used in manufacturing urban\nmaterials. Photolysis did not significantly impact the chemical composition\nof OA emitted from the burning of specific WUI materials.