AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Characterization of Oligomers Products from Heterogeneous Acid-Catalyzed Reaction of Methyl Vinyl Ketone and Their Formation Reaction Mechanisms
Ka M. Chan, Dan D. Huang, Yong J. Li, Man N. Chan, John Seinfeld, CHAK K. CHAN, Hong Kong University of Science and Technology
Abstract Number: 203 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosols (SOA) formation involves complex chemical processes in atmosphere. In this work, the heterogeneous acid-catalyzed reactions of gas-phase methyl vinyl ketone (MVK) with inorganic particles were investigated in a flow reaction system. MVK is one of the most important products from isoprene oxidation. The effects of particle composition and relative humidity (RH) on product formation were explored. Reactions on ammonium sulfate, ammonium bisulfate and sulfuric acid particles were studied. The experiments were conducted at RH40% and RH80%. Ultra-performance liquid chromatograph equipped with an electrospray ionization time-of-flight mass spectrometry (UPLC/ESI-TOFMS) and gas chromatography-mass spectrometry (GC-MS) were utilized to identify particle phase products for developing the reaction mechanisms.
Products in particle phase were detected when ammonium bisulfate and sulfuric acid particles were used. However no product was found when ammonium sulfate particles were used. Oligomeric products formed by i) acid-catalyzed hydration followed by oligomerization or ii) acid-catalyzed aldol reaction. Sulfuric acid particles yielded more and higher order oligomers up to hexamers than ammonium bisulfate did. Moreover, the acid-catalyzed aldol reaction occurred only in sulfuric acid particles but acid-catalyzed hydration followed by oligomerization occurred in both ammonium bisulfate and sulfuric acid particles. High relative humidity was found to favor hydration and facilitate the subsequent acid-catalyzed oligomerization. The formation of higher order oligomers suggests that reactive uptake of MVK could contribute significantly to SOA.
Acknowledgement: This work was supported by the Research Grants Council of Hong Kong (Project No. 610909).