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Limononic acid (3-isopropenyl-6-oxoheptanoic acid, LA), as an important precursor of secondary organic aerosols (SOA), has attracted extensive attention in the field of atmospheric chemistry. However, its microscopic oxidation mechanism is still unclear. In this study, the density functional theory calculations were conducted to study the oxidation mechanism of LA by ·OH in aqueous phase. The results show that the reactions of hydroxylation are more likely to occur than the dehydrogenation reaction, because of the lower free energy barrier (2.3–5.4 kcal mol−1). At 298 K, the total rate constant of the reaction initiated by ·OH is 1.06 × 1010 M−1 s−1, which fits the experimental value well. Among all reactions, the hydroxylation reaction in C 9 site of LA is the most favorable pathway, and the corresponding hydroxylation intermediate (IM4) can react with ·OH, H 2 O, dissolved O 2 , and HO 2 ·. Three important tropospheric free radicals (R·, RO· and RO 2 ·) are generated during the subsequent reaction process. Meanwhile alcohols, ketones, aldehydes, and oxidized acids can be formed in the overall reaction scheme. These products are the precursor for the formation of SOA, and this transformation process will increase the O/C ratio of aqueous phase SOA. This study has an important significance for understanding the oxidation mechanism of monoterpenoids in the atmospheric aqueous phase. [Display omitted] • OH-addition reaction of C 9 site is more like to occur of LA. • The intermediate can react with ·OH, H 2 O, dissolved O 2 , and HO 2. • Three important tropospheric free radicals (R·, RO· and RO 2 ·) are generated during the reaction process. • The transformation process will increase the O/C ratio of aqueous phase SOA. [ABSTRACT FROM AUTHOR]

3,4-dihydroxy-2-butanone (DHBO) is a major oxidation product of IEPOX and can easily be oxidized in tropospheric aqueous phase. The aqueous oxidation mechanism of DHBO has investigated by DFT and initial reaction rate constants also have calculated through TST. In the aqueous phase, the following trend in reactivity of initial reaction can be obtained: OH ≫ SO 4 − > NO 3 , which bases on the calculated rate constants (k (OH) = 1.20 × 108 L mol−1 s−1, k (SO 4 −) = 8.51 × 105 L mol−1 s−1 and k(NO 3) = 2.86 × 105 L mol−1 s−1) at 298 K and 1 atm. After initial reaction, the major products of DHBO further react with OH radical at presence of O 2. The final products include acetic acid and methylglyoxal, which are important SOA precursors. This work provides a reference for oxidation mechanism of dihydroxycarbonyl of isoprene-driven in aqueous and help understand SOA formation. Image 1 • The aqueous oxidation mechanism of DHBO has been studied. • The OH.•-initiated reaction rate constant is 1.20 × 108 L mol−1 s−1 at 298 K and 1 atm. • Acetic acid and methylglyoxal of main products contribute to aqSOA formation. • The HO 2 and RO 2 of minor products increase the ozone yield. [ABSTRACT FROM AUTHOR]