Preprints
https://doi.org/10.5194/egusphere-2026-2191
https://doi.org/10.5194/egusphere-2026-2191
23 Apr 2026
 | 23 Apr 2026

Methanesulfonic and sulfuric acids are major contributors to tropical Indo-Pacific aerosol

Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius

Abstract. In the marine environment dimethylsulfide (DMS) is the most abundant sulfur-containing trace gas. It serves as a key precursor to new particle formation and growth via its oxidation products, sulfuric acid (SA, H2SO4) and methanesulfonic acid (MSA, CH3SO3H). Here, we present measurements of MSA and SA in the Indo-Pacific region during the CAFE-Pacific (Chemistry of the Atmosphere Field Experiment in the Pacific) campaign in January–February 2024. The measurements were conducted on board the HALO (High Altitude and LOng-range) aircraft using nitrate mass spectrometry. We observe gas-phase concentrations of up to 4 × 107 cm-3 MSA and 6 × 107 cm-3 SA in the marine boundary layer. In the lower free troposphere, the MSA/SA ratio increases with altitude in agreement with the temperature-dependent DMS oxidation. At higher altitudes, adiabatic heating and subsequent evaporation of acidic particles within the instrument inlet enable the detection of both particle- and gas-phase MSA and SA. A detailed analysis of two flights shows that marine deep convection can lead to DMS transport from the boundary layer to the upper troposphere and subsequent particle formation and growth after approximately 10–20 hours of OH exposure aligning with the DMS lifetime determined by kinetic modelling. We frequently observe MSA concentrations significantly exceeding those of SA, suggesting that free-tropospheric particles – particularly over the Indo-Pacific Warm Pool – may be dominated by MSA. Our results imply that marine convection represents an important source of airborne particles in the upper tropical troposphere, one of the most pristine regions of Earth's atmosphere.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Journal article(s) based on this preprint

01 Sep 2026
Aircraft observations suggest an important contribution of methanesulfonic and sulfuric acids to tropical Indo-Pacific aerosol
Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius
Atmos. Chem. Phys., 26, 12355–12393, https://doi.org/10.5194/acp-26-12355-2026,https://doi.org/10.5194/acp-26-12355-2026, 2026
Short summary
Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2026-2191', Anonymous Referee #1, 21 May 2026
  • RC2: 'Comment on egusphere-2026-2191', Anonymous Referee #2, 27 May 2026
  • RC3: 'Comment on egusphere-2026-2191', Anonymous Referee #3, 27 May 2026
  • AC1: 'Comment on egusphere-2026-2191', Hannah Klebach, 28 Jul 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Hannah Klebach on behalf of the Authors (28 Jul 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (06 Aug 2026) by Chiara Giorio
RR by Anonymous Referee #2 (07 Aug 2026)
RR by Anonymous Referee #1 (10 Aug 2026)
RR by Anonymous Referee #3 (16 Aug 2026)
ED: Publish as is (16 Aug 2026) by Chiara Giorio
AR by Hannah Klebach on behalf of the Authors (21 Aug 2026)

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2026-2191', Anonymous Referee #1, 21 May 2026
  • RC2: 'Comment on egusphere-2026-2191', Anonymous Referee #2, 27 May 2026
  • RC3: 'Comment on egusphere-2026-2191', Anonymous Referee #3, 27 May 2026
  • AC1: 'Comment on egusphere-2026-2191', Hannah Klebach, 28 Jul 2026

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload
AR by Hannah Klebach on behalf of the Authors (28 Jul 2026)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (06 Aug 2026) by Chiara Giorio
RR by Anonymous Referee #2 (07 Aug 2026)
RR by Anonymous Referee #1 (10 Aug 2026)
RR by Anonymous Referee #3 (16 Aug 2026)
ED: Publish as is (16 Aug 2026) by Chiara Giorio
AR by Hannah Klebach on behalf of the Authors (21 Aug 2026)

Journal article(s) based on this preprint

01 Sep 2026
Aircraft observations suggest an important contribution of methanesulfonic and sulfuric acids to tropical Indo-Pacific aerosol
Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius
Atmos. Chem. Phys., 26, 12355–12393, https://doi.org/10.5194/acp-26-12355-2026,https://doi.org/10.5194/acp-26-12355-2026, 2026
Short summary
Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius
Hannah Klebach, Martin Heinritzi, Katharina Kaiser, Lisa Beck, Samuel Ruhl, Samira Atabakhsh, Nirvan Bhattacharyya, Lucía Caudillo-Plath, Philipp Joppe, Thomas Klimach, Peter Lloyd, Mira Pöhlker, Ulrich Pöschl, Sarah Richter, Douglas M. Russell, Johannes Schneider, Marcel Zauner-Wieczorek, and Joachim Curtius

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Short summary
Marine atmospheric aerosols remain a major uncertainty in climate models. We report gas and particle phase measurements of two important aerosol forming vapours, sulfuric acid and methanesulfonic acid in the Indo-Pacific. We find that the latter typically dominates over sulfuric acid and contributes significantly to free tropospheric aerosol. Deep convection transports the precursor of both acids to the upper troposphere, providing a key aerosol source in the pristine remote Pacific Ocean.
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