Reaction of α-cedrene with ozone: mechanism, gas and particulate products distribution

The gas-phase reaction of ozone with α-cedrene (I) in the absence and presence of an OH radical scavenger (cyclohexane) has been studied in the outdoor 25 m3 Teflon film chambers at the UNC smog chamber facility. Twenty-two compounds were identified for the first time in this study. Important products identified and semi-quantified were α-cedronaldehyde (VI), α-cedronic acid (VIII), α-cedrinic acid (X), α-norcedronaldehyde (VII), 8-hydroxy-9-α-cedranone (III), and α-norcedronic acid (IX). Acetone, formaldehyde, and acetaldehyde also were identified in this study. On average, measured gas and particle phase products accounted for 56% of the reacted α-cedrene. The total yield of products bearing hydroxy groups (e.g. 8-hydroxy-9-α-cedranone (III)) and aldehydes (e.g. α-cedronaldehyde (VI), α-norcedronaldehyde (VII)) was found to be slightly dependent on the presence of an OH radical scavenger. Generally, the aldehyde yield was found to be higher when cyclohexane was present, and the hydroxy compounds yield was higher when cyclohexane was absent. All products identified in this study were found in the particle phase. α-Cedrinic acid (X), α-cedronic acid (VIII), and α-cedronaldehyde (VI) were observed in the early stage in the aerosol phase and may play an important role in the early formation of SOA. Detailed reaction schemes leading to most reaction products observed here are presented and discussed.