Atmospheric breakdown kinetics and air quality impact of potential “green” solvents the oxymethylene ethers OME3 and OME4

Abstract. Laboratory-based experiments were used to investigate the atmospheric degradation chemistry of two oxymethylene ethers, CH₃O(CH₂O)₃CH₃ (OME3) and CH₃O(CH₂O)₄CH₃ (OME4). OME3 and OME4 have been proposed as promising “green” replacement compounds for problematic ethereal solvents such as 1,4-dioxane and tetrahydrofuran. Results from direct, absolute laser-based experiments and from a series of complementary relative rate studies demonstrated that OH + OME3 (R3) proceeded with a rate coefficient k₃(296 K) = (1.0 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, a factor of two smaller than predicted by structure activity relationships (SAR). Evidence for a complex mechanism was provided by k₃(294 – 464 K), characterised by deviations from Arrhenius-like behaviour close to room temperature. A further series of relative rate experiments were used to determine a rate coefficient of k₄(296 K) = (1.1 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for OH + OME4. These results allowed for lifetimes, 𝜏 ≈ 1 day to be estimated for the removal of each of OME3 and OME4 from the troposphere. Photochemical Ozone Creation Potential estimates (POCP_E) were calculated for NW-Europe conditions. These were considerably smaller than equivalent metrics for the problematic solvents they may replace, largely owing to their lack of C-C bonds. In the course of this work, rate coefficients (in 10⁻¹¹ cm³ molecule⁻¹ s⁻¹) were determined for Cl + OME3, k₆(296 K) = (17 ± 4) and for Cl + OME4, k₇(296 K) = (19 ± 6).