Isoprene (C5H8) is the non-methane hydrocarbon with the highest emissions to the atmosphere. It is mainly produced by vegetation, especially broad-leaved trees, and efficiently transported to the upper troposphere in deep convective clouds, where it is mixed with lightning NOx. Isoprene oxidation products drive rapid formation and growth of new particles in the tropical upper troposphere. However, isoprene oxidation pathways at low temperatures are not well understood. Here, in experiments at the CERN CLOUD chamber at 223 K and 243 K, we find that isoprene oxygenated organic molecules (IP-OOM) all involve two successive <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41467_2025_64229_Article_IEq1.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="33" /> </InlineMediaObject> <EquationSource Format="TEX">${{{\rm{OH}}}}^{\bullet}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <mi mathvariant="normal">OH</mi> </mrow> <mrow> <mo>∙</mo> </mrow> </msup> </math></EquationSource> </InlineEquation> oxidations. However, depending on the ambient concentrations of the termination radicals (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41467_2025_64229_Article_IEq2.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="81" /> </InlineMediaObject> <EquationSource Format="TEX">${{{{\rm{HO}}}}_{2}}^{\bullet},\,{{{\rm{NO}}}}^{\bullet}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mrow> <msub> <mrow> <mi mathvariant="normal">HO</mi> </mrow> <mrow> <mn>2</mn> </mrow> </msub> </mrow> <mrow> <mo>∙</mo> </mrow> </msup> <mo>,</mo> <mspace width="0.25em" /> <msup> <mrow> <mi mathvariant="normal">NO</mi> </mrow> <mrow> <mo>∙</mo> </mrow> </msup> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41467_2025_64229_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="33" /> </InlineMediaObject> <EquationSource Format="TEX">${{{\rm{NO}}}}_{2}^{\bullet}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi mathvariant="normal">NO</mi> </mrow> <mrow> <mn>2</mn> </mrow> <mrow> <mo>∙</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation>), vastly-different IP-OOM emerge, comprising compounds with zero, one or two nitrogen atoms. Our findings indicate high IP-OOM production rates for the tropical upper troposphere, mainly resulting in nitrate IP-OOM but with an increasing non-nitrate fraction around midday, in close agreement with aircraft observations.

Isoprene chemistry under upper-tropospheric conditions

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2025年9月29日

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Douglas M. Russell,
Felix Kunkler,
Jiali Shen,
Matthias Kohl,
Jenna DeVivo,
Nirvan Bhattacharyya,
Christos Xenofontos,
Hannah Klebach,
Lucía Caudillo-Plath,
Mario Simon,
Emelda Ahongshangbam,
João Almeida,
Antonio Amorim,
Hannah Beckmann,
Mattia Busato,
Manjula R. Canagaratna,
Anouck Chassaing,
Romulo Cruz-Simbron,
Lubna Dada,
Philip Holzbeck,
Bernhard Judmaier,
Milin Kaniyodical Sebastian,
Paap Koemets,
Timm Krüger,
Lu Liu,
Monica Martinez,
Bernhard Mentler,
Aleksandra Morawiec,
Antti Onnela,
Tuukka Petäjä,
Pedro Rato,
Mago Reza,
Samuel Ruhl,
Wiebke Scholz,
Eva Sommer,
António Tomé,
Yandong Tong,
Jens Top,
Nsikanabasi Silas Umo,
Gabriela R. Unfer,
Ryan X. Ward,
Jakob Weissbacher,
Boxing Yang,
Wenjuan Yu,
Marcel Zauner-Wieczorek,
Imad Zgheib,
Jiangyi Zhang,
Zhensen Zheng,
Imad El Haddad,
Richard C. Flagan,
Armin Hansel,
Heikki Junninen,
Markku Kulmala,
Katrianne Lehtipalo,
Jos Lelieveld,
Ottmar Möhler,
Siegfried Schobesberger,
Rainer Volkamer,
Paul M. Winkler,
Douglas R. Worsnop,
Theodoros Christoudias,
Andrea Pozzer,
Neil M. Donahue,
Hartwig Harder,
Jasper Kirkby,
Xu-Cheng He,
Joachim Curtius

摘要

Isoprene (C₅H₈) is the non-methane hydrocarbon with the highest emissions to the atmosphere. It is mainly produced by vegetation, especially broad-leaved trees, and efficiently transported to the upper troposphere in deep convective clouds, where it is mixed with lightning NO_x. Isoprene oxidation products drive rapid formation and growth of new particles in the tropical upper troposphere. However, isoprene oxidation pathways at low temperatures are not well understood. Here, in experiments at the CERN CLOUD chamber at 223 K and 243 K, we find that isoprene oxygenated organic molecules (IP-OOM) all involve two successive ${{{\rm{OH}}}}^{\bullet}$ ${OH}^{∙}$ oxidations. However, depending on the ambient concentrations of the termination radicals ( ${{{{\rm{HO}}}}_{2}}^{\bullet},\,{{{\rm{NO}}}}^{\bullet}$ ${HO}_{2}^{∙}, {NO}^{∙}$ , and ${{{\rm{NO}}}}_{2}^{\bullet}$ ${NO}_{2}^{∙}$ ), vastly-different IP-OOM emerge, comprising compounds with zero, one or two nitrogen atoms. Our findings indicate high IP-OOM production rates for the tropical upper troposphere, mainly resulting in nitrate IP-OOM but with an increasing non-nitrate fraction around midday, in close agreement with aircraft observations.