Key parameters controlling OH-initiated formation of secondary organic aerosol in the aqueous phase (aqSOA)

Barbara Ervens, Armin Sorooshian, Yong B. Lim, Barbara J. Turpin

Research output: Contribution to journalArticle

58 Scopus citations


Secondary organic aerosol formation in the aqueous phase of cloud droplets and aerosol particles (aqSOA) might contribute substantially to the total SOA burden and help to explain discrepancies between observed and predicted SOA properties. In order to implement aqSOA formation in models, key processes controlling formation within the multiphase system have to be identified. We explore parameters affecting phase transfer and OH(aq)-initiated aqSOA formation as a function of OH(aq) availability. Box model results suggest OH(aq)-limited photochemical aqSOA formation in cloud water even if aqueous OH(aq) sources are present. This limitation manifests itself as an apparent surface dependence of aqSOA formation. We estimate chemical OH(aq) production fluxes, necessary to establish thermodynamic equilibrium between the phases (based on Henry's law constants) for both cloud and aqueous particles. Estimates show that no (currently known) OH(aq) source in cloud water can remove this limitation, whereas in aerosol water, it might be feasible. Ambient organic mass (oxalate) measurements in stratocumulus clouds as a function of cloud drop surface area and liquid water content exhibit trends similar to model results. These findings support the use of parameterizations of cloud-aqSOA using effective droplet radius rather than liquid water volume or drop surface area. Sensitivity studies suggest that future laboratory studies should explore aqSOA yields in multiphase systems as a function of these parameters and at atmospherically relevant OH(aq) levels. Since aerosol-aqSOA formation significantly depends on OH(aq) availability, parameterizations might be less straightforward, and oxidant (OH) sources within aerosol water emerge as one of the major uncertainties in aerosol-aqSOA formation. Key Points AqSOA formation in clouds is oxidant limited but possibly not in aerosol particlesCloud aqSOA formation inversely scales with drop effective radiusObserved trends of cloud aqSOA show agreement with model results.

Original languageEnglish (US)
Pages (from-to)3997-4016
Number of pages20
JournalJournal of Geophysical Research: Space Physics
Issue number7
Publication statusPublished - 2014



  • aqueous phase
  • oxidants
  • secondary organic aerosol

ASJC Scopus subject areas

  • Atmospheric Science
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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