The Pressure Dependency of Stabilized Criegee Intermediate Yields of Selected Ozone-Alkene Reactions

Tuesday, 16 December 2014
Jani P Hakala1,2 and Neil McPherson Donahue2, (1)University of Helsinki, Helsinki, Finland, (2)Carnegie Mellon Univ, Pittsburgh, PA, United States
Stabilized Criegee Intermediates (SCI) play an important role as an oxidizing species in atmospheric reactions. The ozonolysis of alkenes in the atmosphere, i.e. the mechanism by which the SCIs are produced, is a major pathway to the formation of Secondary Organic Aerosols (SOA) in the atmosphere. Just how much SCIs contribute to the SOA formation is not well known and fundamental research in the kinetics of SCI formation need to be performed to shed light on this mystery.

The alkene ozonolysis is highly exothermic reaction, so a third body is needed for stabilizing the SCI, thus making the SCI yield pressure dependent. We studied the production of SCIs at different pressures by studying their ability to oxidize sulfur dioxide in a pressure controlled flow reactor. We used a mixture of ultra-high purity nitrogen, oxygen, and a selective scavenger for hydroxyl radical (OH) as a carrier gas, and injected a mixture of nitrogen, sulfur dioxide and selected alkene to the center of the flow for ozonolysis to take place. With the OH radical scavenged, the SCI yield of the reaction was measured by measuring the amount of sulfuric acid formed in the reaction between SCI and sulfur dioxide with a Chemical Ionization Mass Spectrometer (CIMS).

This work was supported by NASA/ROSES grant NNX12AE54G to CMU and Academy of Finland Center of Excellence project 1118615.