O3 oxidation of SO2 in sea-salt aerosol water: Size distribution of non-sea-salt sulfate during the First Aerosol Characterization Experiment (ACE 1)

H. Sievering, B. Lerner, J. Slavich, J. Anderson, M. Posfai, J. Cainey

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Abstract

Non sea-salt sulfate (NSS) of 2.2-23 nmol m-3 total magnitude in aerosols observed during the First Aerosol Characterization Experiment (ACE-1) at Cape Grim, Tasmania, was trimodally distributed with ∼1 nmol NSS m-3 in >0.7 μm ambient diameter (diam) coarse sea-salt mode aerosols; despite this low NSS concentration, [H2SO4(g)] was so low that <1% of this NSS could have been due to H2SO4 scavenging. Ammonium was not associated with these coarse sea-salt aerosols, suggesting that cloud processing was a minor contributor to the NSS found in >0.7 μm diam aerosols. The mechanism of O3 oxidation of SO2 in sea-salt aerosol water (SSAW) is assessed for its capability to explain this coarse aerosol NSS. Limitation of this mechanism's NSS contribution is largely due to SSAW's buffering capacity since its reaction rate is reduced by 2 orders of magnitude at pH 6 versus the pH ≥ 8 of unreacted SSAW. However, the buffering capacity of sea-salt aerosols may have been significantly enhanced over that of bulk seawater alkalinity. This appears to be due to carbonate resulting from small fragments of biogenic CaCO3 in the ocean's surface microlayer. Given the observed nonsoil calcium excess over that in bulk seawater, the estimated actual buffering capacity of sea-salt aerosols observed during ACE 1 was 50%, or more, enhanced over that due to bulk seawater alkalinity. Considering this enhanced buffering capacity, O3 oxidation of SO2 in SSAW can produce sufficient NSS to explain 70-90% of the ∼1 nmol m-3 found in >0.7 μm diam coarse sea-salt aerosols with cloud processing and further oxidation of SO2 in SSAW (i.e., pH < 6) by other sea-salt conversion mechanisms contributing the remainder. The amount of NSS produced by sea-salt conversion mechanisms during the ACE 1 remote Southern Ocean experiment vied with homogeneous and cloud processing in their contribution to the total observed NSS of 2.2-2.3 nmol m-3.

Original languageEnglish
Article number1998JD100086
Pages (from-to)21707-21717
Number of pages11
JournalJournal of Geophysical Research Atmospheres
Volume104
Issue numberD17
DOIs
Publication statusPublished - Sep 20 1999

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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