SOA Formation from the Ozonolysis of Various Sesquiterpenes and the Photooxidation of Their First Generation Products

CHRISTINA N. VASILAKOPOULOU, Agata Kołodziejczyk, Kalliopi Florou, Christos Kaltsonoudis, Angeliki Matrali, Damianos Pavlidis, Spyros Ν. Pandis, University of Patras, Greece

     Abstract Number: 307
     Working Group: Carbonaceous Aerosol

Abstract
The oxidation of biogenic volatile organic compounds is an important pathway of the formation of secondary organic aerosol (SOA). The SOA formation by isoprene and the monoterpenes has been studied extensively, however less is known about the role of sesquiterpenes. Laboratory chamber experiments were conducted in order to study the SOA formation from the ozonolysis of various sesquiterpenes (b-caryophyllene, a-humulene, d-cadinene) as well as from the reactions of three of their products (b-nocaryophyllinic acid, 2-(2-carboxyethyl)-3,3-dimethylcyclobutanecarboxylic acid and 2-(2-methyl-6-oxoheptan-3-yl)-3,6-dioxoheptanal) with the OH radical. These products were synthesized for the purposes of this study. The investigation of their oxidation allows the quantification of the role of later generation reactions in the system and the potential additional SOA formation.

The particle phase was continuously characterized using an aerosol mass spectrometer (AMS), the CHARON/PTR-MS and a scanning mobility particle sizer (SMPS). A high resolution PTR-MS and standard gas monitors were used for the measurements of the various compounds in the gas phase. Samples were also collected at the end of each experiment, which were analyzed with LC-MS.

Our results indicate that the produced SOA from sesquiterpenes can eventually become quite oxidized having O:C around 0.7. Previous experimental work has suggested that the final O:C of sesquiterpene SOA is much lower. Also, a number of the first generation products continue reacting and the SOA mass spectrum evolves rapidly. The AMS spectrum changed by 20-25 degrees as the fresh SOA was aging. This suggests that identification of the corresponding SOA under ambient conditions based on the first generation products may be problematic. The composition of the fresh and the aged SOA and the implications for the quantification of the sesquiterpene SOA in the field will be discussed.