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

Abstract

Vapor wall loss has only recently been shown a potentially significant bias in atmospheric chamber studies. Yet, previous works aimed 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 of 15 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 m 3 Teflon atmospheric chamber, and aged for 4 hours (equivalent to 5 -8 hours in the atmosphere). The particle phase compound concentrations were monitored using a Thermal Desorption Aerosol Gas Chromatograph coupled to a High-Resolution -Time of FlightMass Spectrometer (TAG-AMS). The observed depletion of the concentration was later modeled using two different 20 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. 25Furthermore we show that 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 * 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. 30Atmos. Chem. Phys. Discuss., https://doi

Evolution of the chemical fingerprint of biomass burning organic aerosol during aging

“…To estimate the loss rate, one would need to conduct a thorough investigation of several key parameters (e.g., each compound's saturation vapor concentration, particle mass accommodation coefficient, or equivalent organic mass concentration at the wall), which are not yet properly constrained within the existing literature. Investigation into vapor wall loss is beyond the scope of this paper but is addressed in Bertrand et al (2018). Concentrations reported here are not corrected for vapor wall loss.…”

“…Therefore, the k OH rate constant derived from these results must be regarded with caution. This is addressed in further detail in Bertrand et al (2018). .…”

“…often reported. These include levoglucosan, a sugar anhydride compound and by-product of the thermal degradation of cellulose and a commonly used tracer of biomass burning organic aerosol (BBOA) in source apportionment (Waked et al, 2014;Bonvalot et al, 2016;Maenhaut et al, 2016), as well as methoxyphenols, by-products of the thermal degradation of lignin. In fresh emissions, the emission factors (EFs) of these compounds can vary with the type of fuel (hardwood, softwood, or herbaceous types; Schmidl et al, 2008b;Schauer et al, 2001;Fine et al, 2002Fine et al, , 2004, the type of fire (open fire, fire places, woodstove; Fine et al, 2002Fine et al, , 2004, or even the sampling setup (in an experimental stack, in a dilution tunnel, or ambient; Nussbaumer et al, 2010).…”

Response to reviewer #2

“…Therefore, the k OH rate constant derived from these results must be regarded with caution. This is addressed in further detail in Bertrand et al (2018 Figure 7. Mean enhancement ratios (ERs) of individual compounds in biomass burning emissions.…”

“…often reported. These include levoglucosan, a sugar anhydride compound and by-product of the thermal degradation of cellulose and a commonly used tracer of biomass burning organic aerosol (BBOA) in source apportionment (Waked et al, 2014;Bonvalot et al, 2016;Maenhaut et al, 2016), as well as methoxyphenols, by-products of the thermal degradation of lignin. In fresh emissions, the emission factors (EFs) of these compounds can vary with the type of fuel (hardwood, softwood, or herbaceous types; Schmidl et al, 2008b;Schauer et al, 2001;Fine et al, 2002Fine et al, , 2004, the type of fire (open fire, fire places, woodstove; Fine et al, 2002Fine et al, , 2004, or even the sampling setup (in an experimental stack, in a dilution tunnel, or ambient; Nussbaumer et al, 2010).…”