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Published April 2019 | Supplemental Material + Published
Journal Article Open

Iodide Accelerates the Processing of Biogenic Monoterpene Emissions on Marine Aerosols


Marine photosynthetic organisms emit organic gases, including the polyolefins isoprene (C_5H_8) and monoterpenes (MTPs, C_(10)H_(16)), into the boundary layer. Their atmospheric processing produces particles that influence cloud formation and growth and, as a result, the Earth's radiation balance. Here, we report that the heterogeneous ozonolysis of dissolved α-pinene by O_3(g) on aqueous surfaces is dramatically accelerated by I–, an anion enriched in the ocean upper microlayer and sea spray aerosols (SSAs). In our experiments, liquid microjets of α-pinene solutions, with and without added I–, are dosed with O_3(g) for τ < 10 μs and analyzed online by pneumatic ionization mass spectrometry. In the absence of I–, α-pinene does not detectably react with O_3(g) under present conditions. In the presence of ≥ 0.01 mM I–, in contrast, new signals appear at m/z = 169 (C_9H_(13)O_3–), m/z = 183 (C_(10)H_(15)O_3–), m/z = 199 (C_(10)H_(15)O_4–), m/z = 311 (C_(10)H_(16)IO_3–), and m/z = 461 (C_(20)H_(30)IO_4–), plus m/z = 175 (IO_3–), and m/z = 381 (I_3–). Collisional fragmentation splits CO_2 from C_9H_(13)O_3–, C_(10)H_(15)O_3– and C_(10)H_(15)O_4–, and I– plus IO– from C_(10)H_(16)IO_3– as expected from a trioxide IOOO•C_(10)H_(16)– structure. We infer that the oxidative processing of α-pinene on aqueous surfaces is significantly accelerated by I– via the formation of IOOO– intermediates that are more reactive than O_3. A mechanism in which IOOO– reacts with α-pinene (and likely with other unsaturated species) in competition with its isomerization to IO_3–accounts for present results and the fact that soluble iodine in SSA is mostly present as iodine-containing organic species rather than the thermodynamically more stable iodate. By this process, a significant fraction of biogenic MTPs and other unsaturated gases may be converted to water-soluble species rather than emitted to the atmosphere.

Additional Information

© 2019 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: January 3, 2019; Accepted: April 15, 2019; Published: April 25, 2019. We thank Sayaka Hayase and Masahiro Kawasaki (Kyoto University) for their help. S.E. was supported by the Japan Society for the Promotion of Sciences Postdoctoral Fellowship for Research Abroad. M.R.H. and A.J.C. acknowledge the support from the National Science Foundation USA, grant AGS-1744353. The authors declare no competing financial interest.

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Supplemental Material - ao9b00024_si_001.pdf


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