Abstract
Abstract. Biomass-burning organic-aerosol (OA) emissions are known to exhibit semi-volatile behavior that impacts OA loading during plume transport. Because such semi-volatile behavior depends in part on OA composition, improved speciation of intermediate and semi-volatile organic compounds (I/SVOCs) emitted during fires is needed to assess the competing effects of primary OA volatilization and secondary OA production. In this study, 18 laboratory fires were sampled in which a range of fuel types were burned. Emitted I/SVOCs were collected onto Teflon filters and solid-phase extraction (SPE) disks to qualitatively characterize particulate and gaseous I/SVOCs, respectively. Derivatized filter extracts were analyzed using comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC-TOFMS). Quality control tests were performed using biomass-burning relevant standards and demonstrate the utility of SPE disks for untargeted analysis of air samples. The observed chromatographic profiles of I/SVOCs in coniferous fuel-derived smoke samples were well correlated with each other, but poorly correlated with other fuel types (e.g., herbaceous and chaparral fuels). Emissions of benzenediol isomers were also shown to be fuel dependent. The combined Teflon and SPE filter data captured differences in gas-particle partitioning of the benzenediol isomers, with hydroquinone having a significantly higher particle-phase fraction than catechol due to its lower volatility. Additionally, the speciated volatility distribution of I/SVOCs in smoke from a rotten-log fire was estimated to evaluate the composition of potentially volatilized primary OA, which was entirely attributed to oxygenated (or other heteroatomic) compounds. The isomer-dependent partitioning and the speciated volatility distributions both suggest the need for better understanding of gas-phase and heterogenous reaction pathways of biomass-burning-derived I/SVOCs in order to represent the atmospheric chemistry of smoke in models.
Highlights
Biomass burning emits high levels of carbonaceous material, including trace gases, black carbon, and primary organic aerosol (POA) (Akagi et al, 2011; Andreae and Merlet, 2001; Bond et al, 2004) that can significantly impact air quality (Kunzli et al, 2006; Liu et al, 2015; Naeher et al, 2007) and climate (Hobbs et al, 1997; Liu et al, 2014)
Leveraging the enhanced speciation capability of GC × GCTOFMS, the goals of this work were 3-fold: (1) demonstrate the potential of solid-phase extraction (SPE) filters for the untargeted analysis of compounds with a wide range of volatilities; (2) qualitatively investigate the diversity of intermediate and semivolatile organic compounds (I/SVOCs) emitted from biomass burning across a range of fuel types; and (3) assess the accuracy of phase-separated SPE measurements to predict gas-particle partitioning of specific compounds emitted from fires
Because SPE filters have not reportedly been used for untargeted analysis of air samples, the extraction efficiency was assessed for a range of standard compounds with regard to both absolute recovery and potential biases compared to extraction from PTFE filters
Summary
Biomass burning emits high levels of carbonaceous material, including trace gases, black carbon, and primary organic aerosol (POA) (Akagi et al, 2011; Andreae and Merlet, 2001; Bond et al, 2004) that can significantly impact air quality (Kunzli et al, 2006; Liu et al, 2015; Naeher et al, 2007) and climate (Hobbs et al, 1997; Liu et al, 2014). Hatch et al.: Measurements of I/SVOCs in biomass-burning smoke other studies have demonstrated negligible or even net loss of OA downwind of fires due to evaporative losses of POA (Akagi et al, 2012; Capes et al, 2008; Jolleys et al, 2012; May et al, 2015). Better understanding of the relative contributions of dilution-induced volatilization and SOA production requires speciation of the intermediate and semivolatile organic compounds (I/SVOCs) in fresh biomassburning smoke and estimation of their propensity to partition between gas and particle phases. Such measurements can further help to assess the available oxidation pathways of SOA precursors (i.e., gas-phase vs heterogeneous oxidation)
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