Comment on egusphere-2023-282

doi:10.5194/egusphere-2023-282-rc1

Abstract

Abstract. Lab-based experimental and computational methods were used to study the atmospheric degradation of two promising “green” solvents: pinacolone, (CH3)3CC(O)CH3 and methyl pivalate, (CH3)3CC(O)OCH3. Pulsed laser photolysis coupled to pulsed laser induced fluorescence was used to determine absolute rate coefficients (in 10−12 cm3 molecule−1 s−1) of k1(297 K) = (1.2 ± 0.2) for OH + (CH3)3CC(O)CH3 (R1) and k2(297 K) = (1.3 ± 0.3) for OH + (CH3)3CC(O)OCH3 (R2), in good agreement with one previous experimental study. Rate coefficients for both reactions were found to increase at elevated temperature, with k1(T) adequately described by k1(297 – 485 K) = 2.1 × 10−12 exp(−200/T) cm3 molecule−1 s−1. k2(T) exhibited more complex behaviour, with a local minimum at around 300 K. In the course of this work, k3(295 – 450 K) for the well-characterised reaction OH + C2H5OH (ethanol, R3) were obtained, in satisfactory agreement with the evaluated literature. UV-vis. spectroscopy experiments and computational calculations were used to explore (CH3)3CC(O)CH3 photolysis (R4). Absorption cross sections for (CH3)3CC(O)CH3, σ4(λ) in the actinic region were larger and the maximum was red-shifted compared to estimates used in current state-of-science models. As a consequence, we note that photolysis (R4) is likely the dominant pathway for removal of (CH3)3CC(O)CH3 from the troposphere. Nonetheless, large uncertainties remain as quantum yields Ï4(λ) remain unmeasured. Lifetime estimates based upon (R1) and (R4) span the range 2–9 days and are consequently associated with a poorly constrained Photochemical Ozone Creation Potential estimate (POCPE). In accord with previous studies, (CH3)3CC(O)CH3 did not absorb in the actinic region, allowing for straightforward calculation of an atmospheric lifetime of ≈ 9 days and a small POCPE ≈ 11.

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