Temperature dependent rate constants for the gas phase reactions of OH radical with first generation products of monoterpenes oxidation: nopinone, limononaldehyde, myrtenal and ketolimonene

Abstract

Rate constants for the gas-phase reactions of hydroxyl radical with first-generation oxidation products of monoterpenes, namely nopinone, ketolimonene, myrtenal and limononaldehyde have been measured using a relative rate technique over the temperature range 298–353 K and atmospheric pressure of air in a 63 L atmospheric chamber. The experiments were conducted using different analytical techniques and different reference compounds. The rate constants obtained at 298 ± 2 K (in units of 10⁻¹¹ cm³ molecule^-l s^-l) are: nopinone 1.82 ± 0.20; ketolimonene 13.2 ± 1.30; myrtenal 5.97 ± 0.80; and limononaldehyde 5.17 ± 0.44. A very weak temperature dependence in the temperature range 298–353 K was obtained for nopinone and limononaldehyde. Meanwhile, ketolimonene and myrtenal show a negative dependence over the temperature range studied. Atmospheric lifetimes towards OH radicals deduced from room temperature rate constants prove that once emitted into the atmosphere, all studied compounds can be degraded in less than one day and thus contribute to the photochemical pollution on a local or regional scale.