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

Abstract

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.