Preprints
https://doi.org/10.5194/gmd-2020-189
https://doi.org/10.5194/gmd-2020-189

Submitted as: model description paper 15 Jul 2020

Submitted as: model description paper | 15 Jul 2020

Review status: a revised version of this preprint was accepted for the journal GMD and is expected to appear here in due course.

A zero-dimensional view of atmospheric degradation of levoglucosan (LEVCHEM_v1) using numerical chamber simulations

Loredana G. Suciu1, Robert J. Griffin2, and Caroline A. Masiello1,3 Loredana G. Suciu et al.
  • 1Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, 77005, USA
  • 2Departmentsof Civil and Environmental Engineeringand Chemical and Biomolecular Engineering, Rice University, Houston, 77005, USA
  • 3Departmentsof Chemistry and Biosciences, Rice University, Houston, 77005, USA

Abstract. Here we developed a zero-dimensional (0-D) modeling framework (LEVCHEM_v1) to provide insights into the atmospheric degradation of a key tracer emitted during biomass burning – levoglucosan (LEV), while additionally exploring its effects on the dynamics of secondary organic aerosols (SOA) and other gases. For this, we updated existing chemical mechanisms (homogeneous gas-phase chemistry and heterogeneous chemistry) in the BOXMOXv1.7 model to include the chemical degradation of LEV and its intermediary degradation products in both phases (gas and aerosol). In addition, we added a gas-particle partitioning mechanism to the model to account for the effect of evaporation and condensation on the phase-specific concentrations of LEV and its degradation products. Comparison of simulation results with measurements from various chamber experiments show that the degradation time scale of LEV varied by phase, with degradation occurring over ~ 1.5–3.5 days and aerosol-phase degradation occurring over ~ 8–21 hours. These relatively short time scales suggest that most of the initial LEV concentration can be lost chemically or deposited locally before being transported regionally. We varied the heterogeneous reaction rate constant in a sensitivity analysis and found that longer degradation time scales of LEV are possible in the gas phase (5 days) and the aerosol phase (7 days), implying that some LEV may be transported regionally. The multiphase chemical degradation of LEV has effects on SOA and other gases. Several first- or second-generation products resulted from its degradation; most of the products include one or two carbonyl groups, one product contains a nitrate group, and a few products show the cleavage of C-C bonds. The relative importance of the products varies depending on the phase and the timing of the maximum concentration achieved during the simulation. Our estimated secondary organic aerosol SOA yields (5–32 %) reveal that conversion of LEV to secondary products is significant and occurs rapidly in the studied scenarios. LEV degradation affected other gases by increasing the concentrations of radicals and decreasing those of reactive nitrogen species. Decreases of the mixing ratios of nitrogen oxides appear to drive a more rapid increase in ozone compared to changes in volatile organic compounds (VOC) levels.

An important next step to confirm longer degradation time scales will be to extend the evaluation of the modeled LEV degradation beyond 3–5 hours, by using more extensive data from chambers, and, possibly from fire plumes. The mechanism developed here can be used in chemical transport models applied to fire plumes to trace LEV and its degradation products from source to deposition, assess their atmospheric implications and answer questions relevant to fire tracing, carbon and nitrogen cycling, and climate.

Loredana G. Suciu et al.

 
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Loredana G. Suciu et al.

Model code and software

LEVCHEM_v1 model files for Suciu et al. A zero-dimensional view of atmospheric degradation of levoglucosan (LEVCHEM_v1) using numerical chamber simulations Suciu, Loredana G.; Griffin, Robert J.; Masiello, Caroline A. https://doi.org/10.5281/zenodo.3885786

Loredana G. Suciu et al.

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Short summary
Understanding the atmospheric degradation of biomass burning tracers such as levoglucosan is essential to decreasing uncertainties in the role of biomass burning in air quality, carbon cycling and paleoclimate. Using a 0-D modeling approach and numerical chamber simulations we found that the multiphase atmospheric degradation of levoglucosan occurs over time scales of hours to days, can form secondary organic aerosols and affects other key tropospheric gases, such as ozone.