Temperature-dependent kinetics of the gas-phase reactions of Cl atoms with nopinone, ketolimonene, and myrtenal

In this study, the gas phase reaction of chlorine atoms with three first-generation oxidation products of monoterpene: (myrtenal C10H14O, nopinone C9H14O, and ketolimonene C9H14O) were investigated using a relative technique method. These compounds result from the atmospheric oxidation of monoterpene compounds such as & alpha;/& beta; - pinene and limonene. Experiments were performed at temperature range 298-353 K and atmospheric pressure in synthetic air bath gas. Cl atoms were generated by UV photolysis of dichloride (Cl-2). The reaction was followed using a proton-transfer reaction mass spectrometer (PTR-MS) and/or Fourier-transform infrared spectroscopy (FTIR) to monitor the concentrations of the investigated species simultaneous with several reference compounds as a function of time. The rate constants were obtained and the Arrhenius expressions (cm(3) molecule(-1) s(-1)) obtained were established over the temperature range of 298-353 K:k(nopinone + Cl) = (5.0 & PLUSMN; 1.2) x 10(-10) exp ( - (406 & PLUSMN; 78) /T)k(ketolimonene + Cl) = (8.88 & PLUSMN; 1.3) x 10(-10) exp( - (246 & PLUSMN; 46)/T)k(myrtenal + Cl) = (13.5 & PLUSMN; 6.4) x 10(-10) exp( - (535 & PLUSMN; 153)/T)Based on rate constants, the atmospheric lifetimes (& tau;) of targeted compounds with respect to reaction with chlorine atoms were estimated and expected to be less than 1 day. There results led to conclude that the reaction with chlorine atoms can be an effective tropospheric loss pathway mainly in regions presenting relatively high chlorine concentrations.