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

Abstract

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 α/β – 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 (Cl₂). 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 (cm³ molecule⁻¹ s⁻¹) obtained were established over the temperature range of 298–353 K:

k_{nopinone + Cl} =  (5.0  ±  1.2) ×  10⁻¹⁰ exp ( − (406  ±  78) /T)

k_{ketolimonene + Cl} =  (8.88 ±  1.3) × 10⁻¹⁰ exp( − (246 ± 46)/T)

k_{myrtenal + Cl} =  (13.5 ±  6.4) × 10⁻¹⁰ exp( − (535 ±  153)/T)

Based on rate constants, the atmospheric lifetimes (τ) 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.