An experimental study of the gas-phase reactions of the NO3 radical with three sesquiterpenes: isolongifolene, alloisolongifolene, and α-neoclovene

Isolongifolene, alloisolongifolene, and α-neoclovene are sesquiterpenes, hydrocarbons of general formula C15H24; these sesquiterpenes contain a single carbon–carbon double bond. They are emitted to the atmosphere by plants during the night and the day. Rate coefficients for the reactions between the night-time atmospheric oxidant, the NO3 radical, and isolongifolene (k1), alloisolongifolene (k2), and α-neoclovene (k3) have been determined at T=298±2 K and P=760±10 Torr by the relative-rate method. The values of the rate constants measured were k1=(3.9±1.6)×10-12 cm3 molecule-1 s-1, k2=(1.4±0.7)×10-12 cm3 molecule-1 s-1 and k3=(8.2±4.6)×10-12 cm3 molecule-1 s-1. The reference reaction for determining k1 and k3 was the reaction between NO3 and α-pinene (k9), and the reference reaction for determining k2 was the reaction between NO3 and cyclohexa-1,4-diene (k10). The values used for the rate constants for the reference reactions are k9=6.2×10-12 cm3 molecule-1 s-1 and k10=6.6×10-13 cm3 molecule-1 s-1, with likely errors of 30% on each. Error limits quoted on our measured rate constants (k1–k3) include these potential errors on k9 or k10. The chemical atmospheric lifetimes of these sesquiterpenes are considered. They are short, and are dominated by the reaction with the NO3 radical by night; OH and O3 both make significant contributions by day.