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Abstract Burning plastic waste releases massive amounts of atmospheric particulate matter (PM), but its chemical composition and health-related properties are largely unelucidated. Here we characterize chemical composition of PM generated from burning common types of plastics and quantify reactive oxygen/chlorine species and PM oxidative potential (OP). We find that plastic burning PM contains high levels of environmentally persistent free radicals (EPFRs), transition metals, and polycyclic aromatic hydrocarbons. In the aqueous phase, PM generates hydrogen peroxide, •OH radicals, and carbon-centered organic radicals, exhibiting high levels of OP as characterized by dithiothreitol (DTT) and OH assays. Remarkably, plastic burning PM is associated with high concentrations of hypochlorous acid. Kinetic model simulations demonstrate that the PM respiratory deposition leads to •OH formation via complex redox reactions among its constituents and antioxidants in lung lining fluid. Our study highlights significant atmospheric and health implications for unregulated plastic burning, particularly common in many areas of developing countries. 

Primary biological aerosol particles (PBAP) and secondary organic aerosols (SOA) both contain organic compounds that share similar chemical and optical properties. Fluorescence is often used to characterize PBAP, however, this may be hindered due to interferences from fluorophores in SOA. Despite extensive efforts to understand the aging of SOA under elevated particle acidity conditions, little is known about how these processes affect fluorescence of SOA and thereby their interference with the measurements of PBAP. The objective of this study is to investigate the fluorescence of SOA and understand the influence of acidity on the optical properties of organic aerosols and potential interference for the analysis of bioaerosols. SOA was generated by O3 or OH-initiated oxidation of d-limonene or -pinene, as well as by OH-initiated oxidation of toluene or xylene. The SOA compounds were then aged by exposure to varying concentrations of aqueous H2SO4 for two days. Absorption and fluorescence spectrophotometry were used to examine the changes in optical properties before and after aging. The key observation was appearance of strongly light-absorbing and fluorescent compounds at pH =  -1 suggesting that acidity is a major driver of SOA aging. The aged SOA from biogenic precursors (d-limonene and -pinene) resulted in stronger fluorescence than aged SOA from toluene and xylene. The absorption spectra of aged SOA changed drastically in shape upon dilution, whereas the shapes of the fluorescence spectra remained the same, suggesting that fluorophores and chromophores in SOA are separate sets of species. The fluorescence spectra of aged SOA overlapped with fluorescence spectra of PBAP, suggesting that SOA exposed to highly acidic conditions can be confused with PBAP detected by fluorescence-based methods. These processes are likely to play a role in the atmospheric regions where high concentrations of H2SO4 persist, such as upper troposphere and lower stratosphere. 

Oxidation of indole by nitrate radical (NO3) was previously proposed to form nitroindole, largely responsible for the brown color of indole secondary organic aerosol (SOA). As there are seven known nitroindole isomers, we used chromatographic separation to show that a single nitroindole isomer is produced in the indole + NO3 reaction, and definitively assigned it to 3-nitroindole by comparison with chromatograms of nitroindole standards. Mass spectra of aerosolized 3-nitroindole particles were recorded with an aerosol mass spectrometer, and directly compared to mass spectra of SOA from smog chamber oxidation of indole by NO3 in order to help identify peaks unique to nitroindole (m/z 162, 132, and 116). Quantum chemical calculations were done to determine the energetics of hypothesized indole + NO3 intermediates and products. The combination of these data suggests a mechanism wherein a hydrogen atom is first abstracted from the N-H bond in indole, followed by isomerization to a carbon-centered radical in the 3-position, and followed by addition of NO2. Alternative mechanisms involving a direct abstraction of an H-atom from a C-H bond or an NO3 addition to the ring are predicted to be energetically unfavorable from large barriers for the initial reaction steps. 

The chemical composition and physical properties of secondary organic aerosol (SOA) generated through OH-initiated oxidation of mixtures containing β-myrcene, an acyclic monoterpene, and d-limonene, a cyclic monoterpene, were investigated to assess the extent of chemical interactions between their oxidation products. The SOA samples were prepared in an environmental smog chamber, and their composition was analyzed offline using ultra-performance liquid chromatography coupled with electrospray ionization high-resolution mass spectrometry (UPLC-ESI-HRMS). Our results suggested that SOA containing β-myrcene showed a higher proportion of oligomeric compounds with low volatility compared to SOA from d-limonene. The formula distribution and signal intensities of the mixed SOA could be accurately predicted by a linear combination of the mass spectra of SOA from individual precursors. Effects of cross-reactions were observed in the distribution of isomeric oxidation products within the mixed SOA, as evidenced by chromatographic analysis. On the whole, β-myrcene and d-limonene appear to undergo oxidation by OH largely independently from each other, with only subtle effects from cross-reactions influencing the yields of specific oxidation products.