Atmospheric Degradation of CH2═C(CH3)C(O)O[CH2]4CH3 by •OH Radicals: Reactivity, POCP, and Carbonyl Formation

Abstract

Relative rate studies of the gas-phase reaction of amyl methacrylate, CH₂═C(CH₃)C(O)O[CH₂]₄CH₃, with ^•OH radicals were performed at (298 ± 2) K and 1000 mbar. The experiments were conducted in an atmospheric Pyrex chamber coupled to in situ Fourier transform infrared spectroscopy (FTIR). The rate coefficient obtained from the average of several experiments was k_AMMA+•OH = (8.10 ± 1.98) × 10^–11 cm³ molecule^–1 s^–1. Additionally, product studies were conducted under conditions similar to those of the kinetic experiments by using in situ FTIR spectroscopy. Pentanal, butanal, and hydroxyacetone were identified as the main reaction products. The initial pathway for the degradation of amyl methacrylate with ^•OH radicals occurs via addition of ^•OH to the >C═C< bond or hydrogen abstraction from the alkyl chain of the ester. The likelihood of hydrogen atom abstraction is 25%, while the addition of hydroxyl radicals to the double bond occurs with a probability of 75%. Based on these outcomes, a degradation mechanism is postulated. Furthermore, the atmospheric implications of the studied reaction were evaluated by estimating the tropospheric lifetime of amyl methacrylate toward ^•OH radicals as τ_OH = 3.43 h. Additionally, the Photochemical Ozone Creation Potential (POCP) of 84 was calculated for the reaction studied. Carbonyl compounds found as reaction products can exert a substantial influence on both air quality and public health.