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Discussion papers
https://doi.org/10.5194/acp-2017-737
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2017-737
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 Aug 2017

Research article | 16 Aug 2017

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

The underappreciated role of nonvolatile cations on aerosol ammonium-sulfate molar ratios

Hongyu Guo1, Athanasios Nenes1,2,3,4, and Rodney J. Weber1 Hongyu Guo et al.
  • 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 2School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
  • 3Institute for Chemical Engineering Sciences, Foundation for Research and Technology – Hellas, Patras, GR-26504, Greece
  • 4Institute for Environmental Research and Sustainable Development, National Observatory of Athens, P. Penteli, Athens, GR-15236, Greece

Abstract. Overprediction of fine particle ammonium-sulfate molar ratios (R) by thermodynamic models is suggested as evidence for an organic film that only inhibits the equilibration of gas phase ammonia (but not water or nitric acid) with aerosol sulfate and questions the equilibrium assumption long thought to apply for submicron aerosol. The ubiquity of such organic films implies significant impacts on aerosol chemistry. We test the organic film hypothesis by analyzing ambient observations with a thermodynamic model and find that R and ammonia partitioning can be accurately reproduced when small amounts of nonvolatile cations (NVC), consistent with observations, are considered in the thermodynamic analysis. Exclusion of NVCs results in predicted R consistently near 2. The error in R is positively correlated with NVC and not organic aerosol mass fraction or concentration. These results strongly challenge the postulated ability of organic films to perturb aerosol acidity or prevent ammonia from achieving gas-particle equilibrium for the conditions considered.

Hongyu Guo et al.
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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Hongyu Guo et al.
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Short summary
Overprediction of fine particle ammonium-sulfate molar ratios (R) by thermodynamic models is suggested as evidence for an organic film that inhibits the condensation of ammonia onto particles, with significant impacts on aerosol chemistry. We test the organic film hypothesis and find that the effects of small amounts of salt and dust is responsible for errors in R. This means that aerosol predictions are more robust than thought before.
Overprediction of fine particle ammonium-sulfate molar ratios (R) by thermodynamic models is...
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