AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Stabilization of Sulfuric Acid Dimer Clusters by Various Basic Gases
COTY JEN, Peter McMurry, David Hanson, University of Minnesota
Abstract Number: 126 Working Group: Aerosol Chemistry
Abstract Nucleation rates depend on both the concentrations of sulfuric acid and of basic gases, such as ammonia and amines. Chen et al. (PNAS, 2012, doi: 10.1073/pnas.1210285109) proposed that this occurs, in part, because "more volatile" sulfuric acid dimer clusters react with basic gases to form stable (i.e. "less volatile") dimers, thereby leading to the high nucleation rates that are observed in the atmosphere. This study explores the stabilization of sulfuric acid dimer by several basic gases. Measurements were conducted using a glass flow reactor which was continuously operated with a steady flow of humidified nitrogen containing sulfuric acid at concentrations of 10$^7 to 10$^9 cm$^(-3). Sulfuric acid concentration was controlled by varying a flow over a bulk reservoir of 98 % sulfuric acid. Temperature was 295-299 K and humidity was ~ 30 %. A known molar flow rate of a basic gas was injected at various points along the flow reactor. The University of Minnesota Cluster CIMS was used to measure sulfuric acid vapor and cluster concentrations. It was found that, for a given concentration of sulfuric acid vapor (A$_1), the dimer concentration (A$_2) increases with increasing concentration of the basic gas, eventually reaching a plateau where cluster concentrations are close to the kinetically limited values (i.e. collision-controlled concentrations that would be expected if sulfuric acid did not evaporate from the dimer). One implication is that the dominant sulfuric acid dimer cluster is stabilized by the base and is still amenable to detection by the Cluster CIMS. Results for ammonia show a smaller effect on the stabilization of the dimer. The Cluster CIMS also detected aminated clusters of the sulfuric acid trimer at low base concentration (< 20 pptv).