Abundances, emissions, and loss processes of the long-lived and potent greenhouse gas octafluorooxolane (octafluorotetrahydrofuran, <i>c</i>-C₄F₈O) in the atmosphere

• Main Authors: M. K. Vollmer, F. Bernard, B. Mitrevski, L. P. Steele, C. M. Trudinger, S. Reimann, R. L. Langenfelds, P. B. Krummel, P. J. Fraser, D. M. Etheridge, M. A. J. Curran, J. B. Burkholder
• Format: Article
• Language: English
• Published: Copernicus Publications 2019-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://www.atmos-chem-phys.net/19/3481/2019/acp-19-3481-2019.pdf

<p>The first atmospheric observations of octafluorooxolane (octafluorotetrahydrofuran, <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span>), a persistent greenhouse gas, are reported. In addition, a complementary laboratory study of its most likely atmospheric loss processes, its infrared absorption spectrum, and global warming potential (GWP) are reported. First atmospheric measurements of <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> are provided from the Cape Grim Air Archive (41<span class="inline-formula">^∘</span>&thinsp;S, Tasmania, Australia, 1978–present), supplemented by two firn air samples from Antarctica, in situ measurements of ambient air at Aspendale, Victoria (38<span class="inline-formula">^∘</span>&thinsp;S), and a few archived air samples from the Northern Hemisphere. The atmospheric abundance in the Southern Hemisphere has monotonically grown over the past decades and leveled at 74&thinsp;ppq (parts per quadrillion, femtomole per mole in dry air) by 2015–2018. The growth rate of <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> has decreased from a maximum in 2004 of 4.0 to <span class="inline-formula">&lt;0.25</span>&thinsp;ppq&thinsp;yr<span class="inline-formula">⁻¹</span> in 2017 and 2018. Using a 12-box atmospheric transport model, globally averaged yearly emissions and abundances of <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> are calculated for 1951–2018. Emissions, which we speculate to derive predominantly from usage of <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> as a solvent in the semiconductor industry, peaked at 0.15 (<span class="inline-formula">±0.04</span>, 2<span class="inline-formula"><i>σ</i></span>)&thinsp;kt&thinsp;yr<span class="inline-formula">⁻¹</span> in 2004 and have since declined to <span class="inline-formula">&lt;0.015</span>&thinsp;kt&thinsp;yr<span class="inline-formula">⁻¹</span> in 2017 and 2018. Cumulative emissions over the full range of our record amount to 2.8 (2.4–3.3)&thinsp;kt, which correspond to 34 Mt of <span class="inline-formula">CO₂</span>-equivalent emissions. Infrared and ultraviolet absorption spectra for <span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> as well as the reactive channel rate coefficient for the <span class="inline-formula">O(¹D)</span>&thinsp;<span class="inline-formula">+</span>&thinsp;<span class="inline-formula"><i>c</i></span>-<span class="inline-formula">C₄F₈O</span> reaction were determined from laboratory studies. On the basis of these experiments, a radiative efficiency of 0.430&thinsp;W&thinsp;m<span class="inline-formula">⁻²</span>&thinsp;ppb<span class="inline-formula">⁻¹</span> (parts per billion, nanomol&thinsp;mol<span class="inline-formula">⁻¹</span>) was determined, which is one of the largest found for synthetic greenhouse gases. The global annually averaged atmospheric lifetime, including mesospheric loss, is estimated to be <span class="inline-formula">&gt;3</span>000 years. GWPs of 8975, 12&thinsp;000, and 16&thinsp;000 are estimated for the 20-, 100-, and 500-year time horizons, respectively.</p>