Abstract
Abstract. The current understanding of secondary organic aerosol (SOA) formation within biomass burning (BB) plumes is limited by the incomplete identification and quantification of the non-methane organic compounds (NMOCs) emitted from such fires. Gaseous organic compounds were collected on sorbent cartridges during laboratory burns as part of the fourth Fire Lab at Missoula Experiment (FLAME-4) and analyzed by two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–ToFMS). The sensitivity and resolving power of GC × GC–ToFMS allowed the acquisition of the most extensive data set of BB NMOCs to date, with measurements for 708 positively or tentatively identified compounds. Estimated emission factors (EFs) are presented for these compounds for burns of six different vegetative fuels, including conifer branches, grasses, agricultural residue, and peat. The number of compounds meeting the peak selection criteria ranged from 129 to 474 among individual burns, and included extensive isomer groups. For example, 38 monoterpene isomers were observed in the emissions from coniferous fuels; the isomeric ratios were found to be consistent with those reported in relevant essential oils, suggesting that the composition of such oils may be very useful when predicting fuel-dependent terpene emissions. Further, 11 sesquiterpenes were detected and tentatively identified, providing the first reported speciation of sesquiterpenes in gas-phase BB emissions. The calculated EFs for all measured compounds are compared and discussed in the context of potential SOA formation.
Highlights
Biomass burning (BB) emissions can strongly influence tropospheric chemistry and climate (Crutzen and Andreae, 1990)
We report only the compounds identified from the filters that were not detected in the blank, background sample, or in the cartridge samples
In the absence of speciated MT measurements, we propose that secondary organic aerosol (SOA) models apply the MT distribution from needle-derived essential oils corresponding to the vegetation mix to yield more reliable results than assuming a single surrogate MT
Summary
Biomass burning (BB) emissions can strongly influence tropospheric chemistry and climate (Crutzen and Andreae, 1990). Several characteristics (Mondello et al, 2008) of two-dimensional gas chromatography–time-offlight mass spectrometry (GC × GC–ToFMS) make it a powerful tool for characterizing the highly complex gas-phase components of smoke These are (1) high resolving power provides enhanced chromatographic separation, (2) thermal modulation at the interface of the primary and secondary columns refocuses eluting peaks leading to significant improvements in signal-to-noise ratio and sensitivity, (3) high ToFMS spectral collection rate allowing up to 500 full mass spectra (m/z 34–500) to be obtained for a given peak eluting from the secondary column (the time evolution of the mass spectra can help deconvolute co-eluting compounds), and (4) distinct compound classes form patterns in the 2-D retention space aiding in compound classification. The first application of GC × GC to broadly characterize the gas-phase emissions of BB is described, including comparisons among the emissions from burns of selected conifer, grass, crop residue, and peat fuel types
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