Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Lab-based experimental and computational methods were used to study the atmospheric degradation of two promising “green” solvents: pinacolone, (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub> and methyl pivalate, (CH<sub>3</sub>)<sub>3</sub>CC(O)OCH<sub>3</sub>. Pulsed laser photolysis coupled to pulsed laser induced fluorescence was used to determine absolute rate coefficients (in 10<sup>−12</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup>) of <em>k</em><sub>1</sub>(297 K) = (1.2 ± 0.2) for OH + (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub> (R<sub>1</sub>) and <em>k</em><sub>2</sub>(297 K) = (1.3 ± 0.3) for OH + (CH<sub>3</sub>)<sub>3</sub>CC(O)OCH<sub>3</sub> (R<sub>2</sub>), in good agreement with one previous experimental study. Rate coefficients for both reactions were found to increase at elevated temperature, with <em>k</em><sub>1</sub>(T) adequately described by k1(297 – 485 K) = 2.1 × 10<sup>−12</sup> exp(−200/<em>T</em>) cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup>. <em>k</em><sub>2</sub>(<em>T</em>) exhibited more complex behaviour, with a local minimum at around 300 K. In the course of this work, <em>k</em><sub>3</sub>(295 – 450 K) for the well-characterised reaction OH + C<sub>2</sub>H<sub>5</sub>OH (ethanol, R<sub>3</sub>) were obtained, in satisfactory agreement with the evaluated literature. UV-vis. spectroscopy experiments and computational calculations were used to explore (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub> photolysis (R<sub>4</sub>). Absorption cross sections for (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub>, σ<sub>4</sub>(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 (R<sub>4</sub>) is likely the dominant pathway for removal of (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub> from the troposphere. Nonetheless, large uncertainties remain as quantum yields <em>Ï</em><sub>4</sub>(λ) remain unmeasured. Lifetime estimates based upon (R<sub>1</sub>) and (R<sub>4</sub>) span the range 2–9 days and are consequently associated with a poorly constrained Photochemical Ozone Creation Potential estimate (POCP<sub>E</sub>). In accord with previous studies, (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>3</sub> did not absorb in the actinic region, allowing for straightforward calculation of an atmospheric lifetime of <span class="ILfuVd NA6bn" lang="en"><span class="hgKElc"><strong>≈</strong></span></span> 9 days and a small POCP<sub>E</sub> <span class="ILfuVd NA6bn" lang="en"><span class="hgKElc"><strong>≈</strong></span></span> 11.
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