On the Role of Aerosol Morphology for the Heterogeneous Hydrolysis of N2O5

YICEN LIU, Yu Yao, Jeffrey H. Curtis, Matthew West, Nicole Riemer, University of Illinois at Urbana-Champaign

     Abstract Number: 123
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
The heterogeneous dinitrogen pentoxide (N₂O₅) hydrolysis contributes to the nocturnal removal of NO_x. Despite major progress in the measurement of the N₂O₅ reaction coefficient (γ_N2O5) for ambient aerosols, it remains challenging to explain the discrepancies found between lab measurements and model parametrizations. In this study, we examined the impact of phase separation on γ_N2O5 for core-shell and well-mixed morphologies. The stochastic particle-resolved model PartMC-MOSAIC was used to generate 100 scenarios that differ in their input parameters, including primary gas and aerosol emissions, as well as meteorological parameters. Each scenario was simulated for 48 hours with hourly output, yielding a total of 4900 populations with different aerosol compositions and mixing states. For each population, we first calculated γ_core-shell based on the assumption that each particle has a core-shell structure consisting of an inorganic core and an organic coating. According to Riemer et al. (2009), γ_core-shell is a function of inorganic mass concentrations and organic coating thickness. We then calculated γ_well-mixed assuming that the organic and inorganic components are mixed together without considering the phase separation. The values of γ_core-shell and γ_well-mixed of each population were compared to quantify the effect of aerosol mixing morphology. Preliminary results show that the phase separation was significant under low NO_x conditions and was negligible under other conditions. Detailed process analysis will be presented to explain our findings.