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

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 proceeded with a rate coefficient k3(296 ± 2 K) = (1.0 ± 0.2) × 10−11 cm3 molec.−1 s−1, a factor of 2 smaller than predicted by structure activity relationships (SARs). 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 ± 2 K) = (1.1 ± 0.4) × 10−11 cm3 molec.−1 s−1 for OH + OME4. These results allowed for lifetimes, τ≈1 d, to be estimated for the removal of each of OME3 and OME4 from the troposphere. The photochemical ozone creation potential estimate (POCPE) was calculated for northwest 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 molec.−1 s−1) were determined for Cl + OME3, k6(296 ± 2 K) = (17 ± 4), and for Cl + OME4, k7(296 ± 2 K) = (19 ± 6).