[A-AS05] 大気化学

[AAS05-P11] Effects of hydroxyl radical exposure on chemical composition of secondary organic aerosol formed from sabinene ozonolysis

*佐藤 圭^1,2、森野 悠¹、今村 隆史¹、梶井 克純^1,2 (1.国立研究開発法人国立環境研究所、2.京都大学)

キーワード：大気汚染、微小粒子状物質、生物起源揮発性有機化合物、高度酸化分子、揮発性既定関数モデル、分子内水素移動反応

Sabinene, a bicyclic monoterpene with an exocyclic double bond, is a major monoterpene emitted from Japanese cedar. We investigated OH initiated aging of secondary organic aerosol (SOA) formed from sabinene ozonolysis using a laboratory environmental chamber. SOA mass concentration and f43 and f44 ratios of SOA were monitored by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer, where f43 and f44 are the ratios of m/z 43 and m/z 44 to total SOA mass, respectively. SOA mass concentration increased immediately after SOA was exposed to OH radicals due to photochemical aging. The f43 ratio, attributed to alcohols, carbonyls, and peroxides, increased only immediately after the start of exposure, whereas the f44 ratio, attributed to carboxylic acids, continuously increased during the exposure. Offline SOA samples collected before and after the exposure to OH radicals were analyzed by a liquid chromatograph negative-mode electrospray ionization mass spectrometer. Major products present in the particle phase were monomeric products, C_8-10H_12-18O_3-6, and dimeric products, C_17-19H_26-32O_7-9. Monomeric products include sabinic acid, norsabinic acid, and sabinalic acid as reported in previous studies. As a result of exposure to OH radicals highly functionalized eight to nine carbon products increased, whereas dimeric products decreased. Formation of highly functionalized products will be explained by gas phase OH initiated reaction of sabinaketone and nine carbon lactones, major gaseous products formed from sabinene ozonolysis. Decrease in dimeric products will be explained by decomposition of dimeric products due to OH initiated oxidation in the particle phase.