The Role of Particle-Phase Criegee Intermediates in the Ozonolysis of Organic Aerosol

RYAN REYNOLDS, Kevin R. Wilson, Lawrence Berkeley National Laboratory

     Abstract Number: 409
     Working Group: Aerosol Chemistry

Abstract
Criegee intermediates (CI) are central to the ozonolysis of unsaturated organic compounds, controlling the formation of both lighter-molecular weight fragmentation reaction products and heavier oligomers through competing unimolecular and bimolecular pathways. In particular, the reaction of thermalized CI with carboxylic acids (RCOOH) to produce oligomeric α-acyloxyalkyl hydroperoxides (AAHPs) is of interest in the chemical transformation of organic compounds in the atmosphere. We investigate this reactive sink of CI in the particle phase under different atmospherically-relevant conditions using aerosol flow tube experiments to study the ozonolysis of model submicron organic aerosol containing an n-alkene (Z-9-tricosene) and different reaction partners, including a saturated RCOOH. Recent experimental results at room temperature have indicated that the CI + RCOOH reaction in the particle phase proceeds much slower than expected given analogous gas-phase measurements, approximately six orders of magnitude slower than the expected diffusion limit in a liquid organic matrix. Companion kinetic modeling efforts suggest that the bimolecular CI + RCOOH reaction is competitive with unimolecular decay of the CI in the particle phase. Further studies of CI + RCOOH and related reactions reveal the impact of multiple factors on the reaction kinetics of this model system, such as temperature dependence and competing heterogeneous processes.