Atmospheric fate of alkoxy radicals: branching ratio of evolution pathways for 1-propoxy, 2-propoxy, 2-butoxy and 3-pentoxy radicals

Abstract

As the last step of VOC oxidation in the atmosphere, the evolution of alkoxy radicals determines the nature and the concentration of the secondary compounds formed. Branching ratios between decomposition and reaction with O₂ of 1-propoxy, 2-propoxy, 2-butoxy and 3-pentoxy radicals have been measured at room temperature and atmospheric pressure in a simulation chamber using FTIR spectroscopy as an analytical device. k_dec/k_O2 is equal to (3.8 ± 0.4) × 10¹⁶, (2.9 ± 0.3) × 10¹⁶, (2.9 ± 0.4) × 10¹⁸ and (4.1 ± 0.8) × 10¹⁸ molecules cm⁻³ for each, respectively. This ratio has been observed to vary, depending on the leaving alkyl group and the class of alkoxy. No additional decomposition due to excited radicals has been observed.