Abstract
Abstract. Vapor wall loss has only recently been shown a potentially significant bias in atmospheric chamber studies. Yet, previous works aiming at the determination of the degradation rate of semi-volatile organic compounds (SVOCs) often did not account for this process. Here, we evaluate the influence of vapor wall loss on the determination of the gas-phase reaction rate kOH of several biomass burning markers (levoglucosan, mannosan, coniferyl aldehyde, 3-guaiacyl propanol, and acetosyringone) with hydroxyl radicals (OH). Emissions from the combustion of beech wood were injected into a 5.5 m3 Teflon atmospheric chamber, and aged for 4 h (equivalent to 5–8 h in the atmosphere). The particle-phase compound concentrations were monitored using a thermal desorption aerosol gas chromatograph coupled to a high-resolution time-of-flight aerosol mass spectrometer (TAG-AMS). The observed depletion of the concentration was later modeled using two different approaches: the previously published approach which does not take into consideration partitioning and vapor wall loss, and an approach with a more complex theoretical framework which integrates all the processes likely influencing the particle-phase concentration. We find that with the first approach one fails to predict the measured markers' concentration time evolution. With the second approach, we determine that partitioning and vapor wall loss play a predominant role in the particle-phase concentration depletion of all the compounds, while the reactivity with OH has a non-significative effect. Furthermore, we show that kOH cannot be determined precisely without a strong constraint of the whole set of physical parameters necessary to formally describe the various processes involved. It was found that the knowledge of the saturation mass concentration C* is especially crucial. Therefore, previously published rate constants of levoglucosan and more generally SVOCs with hydroxyl radicals inferred from atmospheric chamber experiments must be, at least, considered with caution.
Highlights
Biomass burning is known to emit a significant amount of organic aerosol (OA) (Bruns et al, 2015; Sippula, 2010) in the atmosphere with consequences on health and the climate (Kanakidou et al, 2005; Pope and Dockery, 2006)
Previously published rate constants of levoglucosan and more generally semi-volatile organic compounds (SVOCs) with hydroxyl radicals inferred from atmospheric chamber experiments must be, at least, considered with caution
Because most of the parameters needed to fully describe the various processes occurring during atmospheric chamber experiments are unknown or subject to large uncertainties, we model, in a first approach, the evolution of the concentration of levoglucosan in the particle phase as measured by TAG-AMS by only considering its reactivity towards OH and the particle wall loss (Hennigan et al, 2010, 2011; Kessler et al, 2010; Lambe et al, 2010; Weitkamp et al, 2007)
Summary
Biomass burning is known to emit a significant amount of organic aerosol (OA) (Bruns et al, 2015; Sippula, 2010) in the atmosphere with consequences on health and the climate (Kanakidou et al, 2005; Pope and Dockery, 2006). Many efforts have been made to quantify the contribution of biomass burning organic aerosol (BBOA) to ambient OA concentrations. Often, these contributions are estimated using molecular markers, i.e., compounds specific to a source and assumed, at least implicitly, to be stable toward atmospheric oxidation and re-volatilization/partitioning processes. The anhydrosugar levoglucosan is a byproduct of the pyrolysis of cellulose and is ubiquitous in our environment. It is a unambiguous organic marker of biomass burning emissions (Simoneit et al, 1999).
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