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.
Influence of the vapor wall loss on the degradation rate constants in chamber experiments of levoglucosan and other biomass burning markers
