Sohyeon Kim (Korea Institute of Science and Technology (KIST))

Jiwon Lee (Korea Institute of Science and Technology (KIST))

Sohyeon Kim (Korea Institute of Science and Technology (KIST))

Ikju Ye (Korea Institute of Science and Technology (KIST))

Jiwon Lee (Korea Institute of Science and Technology (KIST))

Biogenic volatile organic compounds (BVOCs) are organic chemicals emitted by plants and other living organisms. These compounds can affect air quality and climate by contributing to the formation of ozone and secondary organic aerosol (SOA). Monoterpenes are a major class of BVOCs with the molecular formula C₁₀H₁₆, but individual monoterpenes differ in molecular structure. In this study, monoterpene isomers were measured using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) to examine their fragment-ion formation. However, individual monoterpene isomers cannot be identified from the protonated molecular-ion signal alone in PTR-ToF-MS because many isomers are predominantly detected at the same m/z. Therefore, differences in fragment-ion formation among the isomers were examined. Five of the most abundant monoterpenes commonly examined in plant studies—α-pinene, β-pinene, limonene, 3-carene, and camphene—were selected and analyzed using PTR-ToF-MS with H₃O⁺ as the reagent ion under varying drift-tube conditions. The major fragment ions commonly observed across the five monoterpenes were m/z 93, 81, and 39, while additional minor fragment ions were observed at m/z 95 and 67. Increasing E/N generally reduced the relative contribution of the protonated molecular ion and increased the relative contributions of fragment ions, indicating greater fragmentation under higher E/N conditions.