AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Chemical Ionization of Sulfuric Acid Clusters Containing Basic Molecules
COTY JEN, Jun Zhao, Peter McMurry, David Hanson, University of Minnesota
Abstract Number: 205 Working Group: Advances in the Physics and Chemistry of New Particle Formation and Growth
Abstract Sulfuric acid clusters are detected by chemical ionization mass spectrometry whereby reagent ions exchange protons with the neutral clusters to form ions. Neutral clusters can also be ionized by these product ions in a process known as ion-induced clustering (IIC). IIC contributions to observed ion signals must be known to obtain accurate measurements of neutral clusters that appear at the same masses. Chemical ionization and IIC of sulfuric acid and its clusters have been previously studied and modeled as chemical reactions between ions and clusters primarily composed of sulfuric acid and water. However in the atmosphere and laboratory measurements, these clusters also contain basic molecules that alter the proton affinities of the clusters. The purpose of this study is to experimentally explore how various basic gases, such as ammonia, methylamine, dimethylamine, trimethylamine, and triethylamine, interact with sulfuric acid clusters, take up protons, and thus potentially alter the ionization reactions and their rate constants. The University of Minnesota Cluster Chemical Ionization Mass Spectrometer (Cluster CIMS) was used to measure cluster response as a function of the basic gas, its concentration, and the ionization reaction time. Experiments were performed inside a continuously purged, glass flow reactor using a well characterized sulfuric acid source. Results indicate that the strongest basic gases neutralize sulfuric acid clusters to the point that they are not efficiently chemically ionized by nitrate ions or by product ions containing sulfuric acid and basic molecules. These results signify that bare sulfuric acid IIC cannot be used for all sulfuric acid/base systems. Ionization rate constants were fitted from data and compared to the collision rate constant of the nitrate/sulfuric acid ionization reaction.