AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Role of Oleic Acid Coating in the Heterogeneous Uptake of Dimethylamine by Ammonium Sulfate Particles
Yangxi Chu, CHAK K. CHAN, City University of Hong Kong
Abstract Number: 501 Working Group: Aerosol Chemistry
Abstract Reactive uptake by ammonium (NH4+) salts is one of the major pathways for the gas-to-particle partitioning of short-chain alkyl amines. Recent studies using particles of individual ammonium salts and mixtures with hydrophilic organics have revealed that the degree of amine uptake depends on the phase state of ammonium salts, the particulate water contents and the particle viscosity. The role of hydrophobic organics, another important category of particulate organics commonly detected in the ambient atmosphere, in amine uptake remains unknown. In this study, we investigated the reactive uptake of dimethylamine (DMA) by ammonium sulfate particles coated with fresh or ozone-aged bulk oleic acid (OA) at 60%, 30% and <5% relative humidities (RHs) using an electrodynamic balance coupled with Raman spectroscopy. OA and DMA were selected to represent hydrophobic organics and alkyl amines, respectively. Over 74% of the original NH4+ ions were displaced due to DMA uptake, except for those experiments performed at <5% RH. On the other hand, the fresh or aged bulk OA coating retarded DMA uptake by preventing the particle surface from effectively accommodating gaseous DMA molecules. Judging from the estimated DMA uptake coefficients, the retardation gradually intensified as the weight percentage of coating increased before levelling off, likely when the particle surface was completely covered by fresh or aged bulk OA. We propose that the accommodation of DMA at the gas-particle interface is the rate-limiting step of overall DMA uptake. Intensive aging of the bulk OA coating had little effect on the equilibrium particle-phase compositions but retarded DMA uptake.