Secondary organic aerosols (SOA) are formed when volatile organic compounds (VOCs) are oxidized in the atmosphere, in either gas-phase or the particle-phase. Over the past years, a significant improvement has been made in understanding the formation, properties and transformation of SOA formed in the particle-phase but there are still a lot of uncertainties that needs to be solved in atmospheric sciences, especially in the aqueous-phase photochemistry. Limononic acid (C9H14O3) oxidation by hydroxyl radicals (OH) in the aqueous-phase was investigated using a relative rate method under acidic and basic conditions. The concentrations of limononic acid and the reference compounds as well as their disappearance in the reaction solution were monitored with liquid chromatography (LC) coupled to the negative electrospray ionization (ESI) quadrupole tandem mass spectrometry (MS/MS). The obtained second order rate constant for the reaction of limononic acid with OH radicals were 1.4 ± 0.3 × 109 M-1s-1 in acidic environment (pH=2) and 0.6 ± 0.03 × 109 M-1s-1 in basic environment (pH=10). These results indicate that the aqueous-phase atmospheric lifetime of limononic acid is pH dependent and that limononic acid will have a shorter photochemical lifetime in acidic solutions. LC-ESI/MS/MS was also used to investigate the reaction mechanism of this oxidation reaction at the molecular level and to explain the SOA formation potential of the limononic acid. Several limononic acid oxidation products were detected with different molecular weights and keto-limononic acid (C9H14O4) was identified as the major product with MW 186 Da.