Hygroscopic properties of smoke-generated 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. Seinfeld2A. Wonaschütz et al. 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
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
Received: 15 Apr 2013 – Discussion started: 06 May 2013 – Revised: 12 Aug 2013 – Accepted: 13 Aug 2013 – Published: 07 Oct 2013
Abstract. During the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE), a plume of organic aerosol was produced by a smoke generator and emitted into the marine atmosphere from aboard the 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, the plume particles had very low hygroscopic growth factors (GFs): between 1.05 and 1.09 for 30 nm and between 1.02 and 1.1 for 150 nm dry size at a relative humidity (RH) of 92%, contrasted by an average marine background GF of 1.6. 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 and 0.88%. Ratios of oxygen to carbon (O : C) and water-soluble organic mass (WSOM) increased with plume age: from < 0.001 to 0.2, and from 2.42 to 4.96 μg m−3, respectively, while organic mass fractions decreased slightly (~ 0.97 to ~ 0.94). High-resolution aerosol mass spectrometer (AMS) spectra show that the organic fragment m/z 43 was dominated by C2H3O+ in the small, new 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, and a GF of 1.04 for an organic mass fraction of 0.35.
