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

Isolongifolene, alloisolongifolene, and alpha-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 (k(1)), alloisolongifolene (k(2)), and alpha-neoclovene (k(3)) 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 k(1) = (3.9 +/- 1.6) x 10(-12) cm(3) molecule(-1) s(-1), k(2) = (1.4 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1) and k(3) = (8.2 +/- 4.6) x 10(-12) cm(3) molecule(-1) s(-1). The reference reaction for determining k(1) and k(3) was the reaction between NO3 and alpha-pinene (k(9)), and the reference reaction for determining k(2) was the reaction between NO3 and cyclohexa-1,4-diene (k(10)). The values used for the rate constants for the reference reactions are k(9) = 6.2 x 10(-12) cm(3) molecule(-1) s(-1) and k(10) = 6.6 x 10(-13) cm(3) molecule(-1) s(-1), with likely errors of 30% on each. Error limits quoted on our measured rate constants (k(1)-k(3)) include these potential errors on k(9) or k(10). 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 O-3 both make significant contributions by day.