AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Role of Particle Composition in the Heterogeneous Reactivity of Carboxylic Acid Aerosol
REBECCA RAPF, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 876 Working Group: Aerosol Chemistry
Abstract The oxidation of organic aerosols in the atmosphere is depends strongly on heterogeneous reactions that are governed by the composition of the aerosol. The reactive fate of carboxylic acid molecules in aerosol is controlled both by exposure to gas-phase oxidants, but also by the nature of the particle phase. For instance, previous modeling studies suggest that acid-base chemistry of an aqueous particle may be competitive with oxidation under some conditions, and this branching between chemical pathways may manifest in the physical characteristics of the particle itself, such as its size. Similarly, changes in molecular packing at the interface can change the heterogeneous reactivity of a particle. Packing and orientation of molecules at the surface is highly dependent on molecular properties, such as the cis- or trans- isomerization of unsaturated carboxylic acids. Direct Analysis in Real Time (DART) ionization mass spectrometry is coupled to a flow tube reactor to monitor the heterogeneous oxidation of size-selected organic aerosols. We report here on the effect of environmental conditions, such as pH, on the heterogeneous oxidation of model systems, including citric acid, and the competition with other pathways, such as acid-base chemistry. Additionally, through analysis of particle size following interaction with the DART source, a probing depth can be calculated, allowing for monitoring surface-sensitive reactions.