AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Particle Size-Dependent Incorporation of Dimethylamine into Ammonium Sulfate and Nitrate Nanoparticles
BRYAN R. BZDEK, Andrew Horan, M. Ross Pennington, Murray Johnston, University of Delaware
Abstract Number: 419 Working Group: Aerosol Chemistry
Abstract It is now established that amines can displace ammonia on the surface of 1-2 nm diameter sulfuric acid-ammonia clusters with near unit efficiency. Exposure of amines to macroscopic ammonium sulfate-coated surfaces has been shown to result in uptake coefficients on the order of 10^-2 to 10^-3. In addition, amines have been shown to slowly displace ammonia in 15-35 micrometer diameter ammonium sulfate particles. While there is now a large body of knowledge concerning amine-ammonia chemistry, reaction rates vary significantly with the type of sample, and the reactivity of amines with ultrafine ammonium salt particles has not been studied. In this work, size-selected ammonium sulfate particles in the 10-30 nm diameter range were sent through a flow tube reactor and exposed to dimethylamine vapor. At the outlet of the flow tube, particle elemental composition was measured quantitatively by the Nano Aerosol Mass Spectrometer. The amount of ammonia displaced by dimethylamine was monitored by the elemental carbon to nitrogen (C/N) ratio. By changing the length of the flow tube, kinetics for the displacement reaction were experimentally determined. Preliminary results indicate that amine incorporation into the particle bulk is highly suppressed, but becomes more favorable as the particle size increases. These observations suggest that increased particulate water content (and a less significant Kelvin effect) as particle size increases may play a key role in modulating the reaction kinetics. The kinetics are consistent with previous work showing ammonium ions on the surface of 1-2 nm diameter clusters exchange quickly with dimethylamine, while those in the cluster “core” exchange slowly if at all.