Impact of humidity on aerosol growth from methanesulfonic acid

Methanesulfonic acid (MSA; CH$_3$SO$_3$H), produced by oxidation of dimethylsulfide (DMS; CH$_3$SCH$_3$), is a key precursor for aerosols in the marine boundary layer and free troposphere. Laboratory experiments show that MSA contributes to both particle nucleation and subsequent growth, often together with sulfuric acid (H$_2$SO$_4$) and base vapours such as ammonia (NH3). However, the influence of relative humidity (RH) on MSA condensation to particles remains uncertain. Here, in experiments conducted under low NH$_3$ conditions (<4 parts per trillion by volume, pptv) at the CERN Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we find that RH critically regulates the participation of MSA in the initial growth of newly formed particles. Between +10 °C and −10 °C, MSA drives rapid particle growth at high RH (>50%), whereas its contribution at low RH (<16%) is negligible. When comparing with aerosol process models such as the Model for Acid–Base Chemistry in Nanoparticle Growth (MABNAG), we find that the model fails to match our laboratory results. In particular, our measurements show that MSA drives rapid particle growth at substantially warmer temperatures and lower relative humidities than predicted by the Extended Aerosol Inorganic Model (E-AIM). This highlights the importance of further experiments to fully quantify the effect of RH on MSA particle growth and evaporation, and incorporating these measurements in aerosol models. This will be essential for accurately representing the important role of MSA in marine aerosols in global models, particularly in cold, low-NH$_3$ environments like polar regions and the free troposphere.

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Publication Details

Journal
KITopen
Published
2026-07-22
DOI
https://doi.org/10.5445/ir/1000195380
Primary Topic
Atmospheric chemistry and aerosols
Type
article
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article

Impact of humidity on aerosol growth from methanesulfonic acid

Arto Heitto, J. Kirkby, Jens Top, Nirvan Bhattacharyya et al.
KITopen
Atmospheric chemistry and aerosols
article

Impact of humidity on aerosol growth from methanesulfonic acid

Arto Heitto, J. Kirkby, Jens Top, Nirvan Bhattacharyya, Marcel Zauner-Wieczorek, Katrianne Lehtipalo, Birte Rörup, Hartwig Harder, Yandong Tong, Douglas R. Worsnop, Lejish Vettikkat, Taina Yli‐Juuti, Rima Baalbaki, Andreas Kürten, T. Christoudias, Paul Winkler, Ruth Konrat, Wiebke Scholz, Lucía Caudillo, Imad El Haddad, Zhensen Zheng, Mario Simon, Armin Hansel, Bernhard Mentler, Jenna DeVivo, Boxing Yang, Christos Xenofontos, Felix Kunkler, Samuel Ruhl, Clara J. Lietzke, Douglas M. Russell, Hannah Klebach, Anouck Chassaing, Pedro Rato, Jakob Weissbacher, Bernhard Judmaier, António Amorim, Neil M. Donahue, Vine Blankenship, Milin Kaniyodical Sebastian, António Tóme, Aleksandra Morawiec, Wenjuan Yu, Jiangyi Zhang, Aenne Jacobshagen, Eva Sommer, Alexandria Stinchfield, Romulo Cruz-Simbron, Hannah Beckmann, Roy Mauldin, Timm Krüger, Rainer Volkamer, Joachim Curtius, Tuukka Petäjä, Ilona Riipinen, Xu-Cheng He, Nsikanabasi Silas Umo, Markku Kulmala, Lu Liu, Gabriela R. Unfer, Lubna Dada, Jiali Shen, Richard Flagan, Ottmar Möhler
article en

Abstract

Methanesulfonic acid (MSA; CH$_3$SO$_3$H), produced by oxidation of dimethylsulfide (DMS; CH$_3$SCH$_3$), is a key precursor for aerosols in the marine boundary layer and free troposphere. Laboratory experiments show that MSA contributes to both particle nucleation and subsequent growth, often together with sulfuric acid (H$_2$SO$_4$) and base vapours such as ammonia (NH3). However, the influence of relative humidity (RH) on MSA condensation to particles remains uncertain. Here, in experiments conducted under low NH$_3$ conditions (<4 parts per trillion by volume, pptv) at the CERN Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we find that RH critically regulates the participation of MSA in the initial growth of newly formed particles. Between +10 °C and −10 °C, MSA drives rapid particle growth at high RH (>50%), whereas its contribution at low RH (<16%) is negligible. When comparing with aerosol process models such as the Model for Acid–Base Chemistry in Nanoparticle Growth (MABNAG), we find that the model fails to match our laboratory results. In particular, our measurements show that MSA drives rapid particle growth at substantially warmer temperatures and lower relative humidities than predicted by the Extended Aerosol Inorganic Model (E-AIM). This highlights the importance of further experiments to fully quantify the effect of RH on MSA particle growth and evaporation, and incorporating these measurements in aerosol models. This will be essential for accurately representing the important role of MSA in marine aerosols in global models, particularly in cold, low-NH$_3$ environments like polar regions and the free troposphere.

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Life below water
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Atmospheric chemistry and aerosols
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