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Multiphase Degradation of Levoglucosan Using 0-D Numerical Simulations: Degradation Time Scales and Effects on SOA and Other Gases
LOREDANA SUCIU, Robert Griffin, Caroline Masiello, Rice University
Abstract Number: 214
Working Group: Aerosol Chemistry
Abstract
Biomass burning is an important source of gases and particles in the atmosphere that impact air quality and climate. Organic molecular tracers, such as levoglucosan (LEV) and its isomers are emitted as both gases and fresh particles. Their properties make them reactive and volatile, thus both chemistry and gas/particle (G/P) partitioning may simultaneously influence their gas-phase and aerosol-phase concentrations in the atmosphere, and implicitly, their atmospheric lifetimes which are still not fully understood. Using a zero-dimensional modeling framework, we developed multiphase chemistry and G/P partitioning mechanisms to study degradation time scales of LEV and the effects of its degradation on secondary organic aerosols (SOA) and other gases. We ran multiple chamber simulations initialized with conditions used in chamber experiments and varying the first-order heterogeneous reaction rate coefficient and the mass accommodation coefficient (α). We found that the model best predicted degradation of aerosol-phase LEV when the heterogeneous reaction rate was slowed down by 2-3 orders of magnitude, at a constant α value (0.001). For these conditions, the resulting degradation time scale varied by phase, respectively 1.5-3.5 days (gas-phase) and 8-21 hours (aerosol-phase). The resulting SOA yields ranged from 5-32%, implying that LEV chemistry can impact air quality. In addition, LEV chemistry influenced other gases such as increasing the mixing ratios of radicals and decreasing those of reactive nitrogen species. The enhanced decay of nitrogen oxides in the presence of multiphase LEV chemistry drove ozone to increase more rapidly compared to changes in volatile organic compounds. Varying the heterogeneous reaction rate suggests that longer degradation time scales of LEV are possible, but to evaluate this finding, more extensive data from chambers or fire plumes are needed in the future.