Monoterpene Oxidation and Air Quality: Kinetics and Formation Pathways of Citronellol with OH Radical

Interactions between the biosphere and atmosphere control the exchange of energy and matter that govern key Earth system processes. Biogenic volatile organic compounds (BVOCs), emitted in large amounts by vegetation, play a central role in atmospheric chemistry. Among them, monoterpenes contribute to tropospheric ozone and secondary organic aerosol formation, affecting both climate and air quality. Their atmospheric oxidation produces oxygenated first-generation terpene oxidation products (TOPs), increasingly observed in forested and mixed environments. Oxygenated monoterpenes, derived from natural substances, are also used as fresheners and in household cleaning products. These compounds are highly reactive in the atmosphere and can affect both indoor and outdoor air quality. One such compound of interest is citronellol (3,7-dimethyl-6-octen-1-ol), which is a major constituent of rose oil and a significant component of bug/insect repellants and hard-surface cleaners. Once in the atmosphere, this compound can be removed through reactions in the gas phase with OH radicals, NO₃ radicals, and ozone. However, data regarding the contribution of its reactivity towards atmospheric oxidants remains limited. Absolute rate coefficients were measured for the first time using a cryogenically cooled flow cell combined with pulsed laser photolysis and laser-induced fluorescence detection of OH radicals. Density functional theory calculations were used to identify dominant reaction pathways, including OH addition and hydrogen abstraction. The results improve understanding of monoterpene oxidation mechanisms and support more accurate representation of biogenic emissions and secondary organic aerosol formation in climate and Earth system models under changing environmental conditions.