Aerosol and Product Yields from NO 3 Radical-Initiated Oxidation of Selected Monoterpenes

Atmospheric transformation of monoterpenes gives products that may cause environmental consequences. In this work the NO 3 radical-initiated oxidation of the monoterpenes α-pinene, β-pinene, Δ 3 -carene, and limonene has been investigated. All experiments were conducted in EUPHORE, the EUropean PHOto REactor facility in Valencia, Spain. The aerosol and product yields were measured in experiments with a conversion of the terpenes in the interval from 7 to 400 ppb. The lower end of the concentrations used are close to those measured in ambient pine forest air. Products were measured using long path in situ FTIR. Aerosol yields were obtained using a DMA-CPC system. The aerosol mass yields measured at low concentrations (10 ppb terpene reacted) were <1, 10, 15, and 17% for α-pinene, β-pinene, Δ 3 -carene, and limonene, respectively. The total molar alkylnitrate yields were calculated to be 19, 61, 66, and 48%, and molar carbonyl compound yields were estimated to be 71, 14, 29, and 69% for α-pinene, β-pinene, Δ 3 -carene, and limonene, respectively. The aerosol yields were strongly dependent on the amounts of terpene reacted, whereas the nitrate and carbonyl yields do not depend on the amount of terpene converted. The principal carbonyl compound from α-pinene oxidation was pinonaldehyde. In the case of limonene, endolim was tentatively identified and appears to be a major product. The reactions with β-pinene and Δ 3 -carene yielded 1−2% of nopinone and 2−3% caronaldehyde, respectively. The results show that it is not possible to use generalized descriptions of terpene chemistry, e.g. in matematical models.