Degradation of air quality in the atmosphere is mainly caused by air pollution and represents a major health risk. Limona ketone (LK) (C₉H₁₄O, 4-acetyl-1-methyl-1-cyclohexene) is emitted by α-pinene, which is massively present in the indoor environment and a major atmospheric source of secondary organic aerosols (SOAs), and has attracted attention in the field of atmospheric chemistry. The OH-addition and H-abstraction reactions of LK by OH radicals have been investigated using M06-2X, ωB97X-D, MP2 and CCSD(T) with the 6-311+G(d,p) basis set. Its degradation channels and reactions with O₂, NO and HO₂ radicals have been explored using quantum chemical methods. The reaction kinetics were studied theoretically over the temperature range of 278–350 K by employing canonical variational transition state theory with the small curvature tunnelling (CVT/SCT) method for both barrierless channels and channels with barriers. The addition of OH at the C1 position of LK at the endocyclic double bond was shown to be the most favourable, with a small relative energy barrier of −7.27 kcal mol⁻¹, and H-abstraction at the C4 position exhibited a relative energy barrier of −1.65 kcal mol⁻¹ at the M06-2X/6-311+G(d,p) level of theory. Our calculated energy results show that the OH addition reactions are more dominant than the H-abstraction channel through electronic rearrangement. The obtained overall rate coefficient at 298 K is 4.77 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, which is in good agreement with the experimental rate coefficient of k_OH = (1.29 ± 0.33) × 10⁻¹⁰ at 296 ± 2 K and ∼735 Torr determined by Atkinson et al. Addition of the OH radical at the C1 position predominates over all the other reaction channels, with a branching ratio of 56.20% at 298 K. Our theoretical results suggest that the atmospheric lifetime is ∼0.58 hours and the formation of stable product 1-(hydroperoxy-4-methylcyclohex-3-en-1-yl) ethenone is thermodynamically exothermic in nature. This work provides valuable information regarding the degradation mechanism and atmospheric fate of LK in the reaction initiated by the OH radical.

Nerol ((Z)-3,7-dimethylocta-2,6-dien-1-ol), (C₁₀H₁₈O), is a monoterpene alcohol that belongs to the family of BVOCs emitted naturally by means of vegetation and is found in various medicinal plants. This species attracted attention in the field of atmospheric chemistry due to its unique structural, chemical and environmental properties. In this work, OH-addition and H-abstraction reactions of Nerol by OH radical have been investigated using M06-2X, CBS-QB3 and CCSD(T) with 6-311++G(d,p) basis set. The OH addition at the C=C double bond of Nerol was shown to be the most favorable, with a small relative energy barrier of −6.86 kcal/mol and H-abstraction at the CH₂ group exhibits a relative energy barrier of 0.08 kcal/mol at CCSD(T)/6-311++G(d,p) level of theory. The obtained overall rate coefficient at 298 K is 9.68 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ using canonical variational transition state theory with small curvature tunnelling method (CVT/SCT), which is in good agreement with the experimental rate coefficient determined by Mahecha et al. (k_OH = (1.60 ± 0.2) × 10⁻¹⁰) at 296 ± 2 K. The obtained rate coefficient exhibits negative temperature dependence, and the atmospheric lifetime of Nerol is about 18 min. The predicted oxidation pathways reveal the formation of key products such as formaldehyde, glycolaldehyde and 6-Methyl-hept-5-en-2-ol, which is also observed in previous experimental studies, indicating good agreement between theoretical and experimental findings. This study constitutes the first theoretical study and its dependence on temperature exploration, offering detailed insights into the degradation pathways and environmental impact of Nerol initiated by hydroxyl radicals.