Kinetics of the reactions of NO3 radical with selected monoterpenes: A temperature dependence study

Terpenes from biogenic sources in the atmosphere are emitted in amounts com parable to those of non-methane organic compounds from antropogenic sources . The aim of this work is to study the reactivity of the terpenes alpha-pin ene, beta-pinene, and camphene toward the NO3 radical in order to evaluate the importance of these reactions in the atmosphere and their atmospheric i mpact. The experiments have been carried out under second-order kinetic con ditions over the temperature range 298-433 K using a discharge flow system and monitoring the NO3 radical by Laser Induced Fluorescence (LIF). The mea sured room-temperature rate constants for reaction of NO3 with alpha-pinene , beta-pinene, and camphene are (cm(3) molecule(-1) s(-1)) (5.9 +/- 0.8) x 10(-12), (2.1 +/- 0.4) x 10(-12), and (0.62 +/- 0.21) x 10(-12), respective ly. The proposed Arrhenius expressions, for the three studied reactions, ar e k(1) = (3.5 +/- 1.4) x 10-(13)exp[(841 +/- 144/T)](cm(3) molecule(-1) s(- 1)), k(2) = (1.6 +/- 1.5) x 10(-10) exp[(-1248 +/- 36/T)] (cm(3) molecule(- 1) s(-1)), and k(3) = (3.1 +/- 0.5) x 10(-12)exp[(-481 +/- 55/T)] (cm(3) mo lecule(-1) s(-1)). A negative activation energy of 7.0 +/- 1.0 kJ mol(-1) h as been found from the temperature dependence of the rate constant for the reaction of cr-pinene with NOB, and positive Values of 10.4 +/- 0.3 and 4.0 +/- 0.5 kJ mol(-1) have been determined for beta-pinene and camphene, resp ectively. Tropospheric half-lives for these terpenes have been calculated a t night and during the day for typical NO3 and OH concentrations and show t hat both radicals provide an effective tropospheric sink for these compound s, and the nighttime reaction with NO3 radical can be an important, if not dominant, loss process for these organics.