Atmos. Chem. Phys. Discuss., 13, 11919-11969, 2013
© Author(s) 2013. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Hygroscopic properties of organic aerosol particles emitted in the marine atmosphere
A. Wonaschütz1, M. Coggon2, A. Sorooshian3,4, R. Modini5,*, A. A. Frossard5, L. Ahlm5,**, J. Mülmenstädt5, G. C. Roberts5,6, L. M. Russell5, S. Dey7, F. J. Brechtel7, and J. H. Seinfeld2
1University of Vienna, Faculty of Physics, Vienna, Austria
2Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA
3Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ, USA
4Department of Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
5Scripps Institution of Oceanography, University of California, San Diego, CA, USA
6Centre National de la Recherche Scientifique – Groupe d'études de l'Atmosphère Météorologique, Toulouse, France
7Brechtel Manufacturing, Inc., Hayward, CA, USA
*now at: Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland
**now at: Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden

Abstract. During the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE), a plume of organic aerosol was produced and emitted into the marine atmosphere from aboard the research vessel R/V Point Sur. In this study, the hygroscopic properties and the chemical composition of the plume were studied at plume ages between 0 and 4 h in different meteorological conditions. In sunny conditions, hygroscopic growth factors (GFs) at a relative humidity (RH) of 92% were low, but increased at higher plume ages: from 1.05 to 1.09 for 30 nm and from 1.05 to 1.1 for 150 nm dry size (contrasted by an average marine background GF of 1.6). Simultaneously, ratios of oxygen to carbon (O:C) increased from < 0.001 to 0.2, water-soluble organic mass (WSOM) concentrations increased from 2.42 to 4.96 μg m−3, and organic mass fractions decreased slightly (~ 0.97 to ~ 0.94). New particles were produced in large quantities (several 10 000 cm−3), which lead to substantially increased cloud condensation nuclei (CCN) concentrations at supersaturations between 0.07–0.88%. High-resolution aerosol mass spectrometer (AMS) spectra show that the organic fragment m/z 43 was dominated by C2H3O+ in the small particle mode and by C3H7+ in the large particle mode. In the marine background aerosol, GFs for 150 nm particles at 40% RH were found to be enhanced at higher organic mass fractions. An average GF of 1.06 was observed for aerosols with an organic mass fraction of 0.53, a GF of 1.04 for an organic mass fraction of 0.35.

Citation: Wonaschütz, A., Coggon, M., Sorooshian, A., Modini, R., Frossard, A. A., Ahlm, L., Mülmenstädt, J., Roberts, G. C., Russell, L. M., Dey, S., Brechtel, F. J., and Seinfeld, J. H.: Hygroscopic properties of organic aerosol particles emitted in the marine atmosphere, Atmos. Chem. Phys. Discuss., 13, 11919-11969, doi:10.5194/acpd-13-11919-2013, 2013.
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