Atmos. Chem. Phys. Discuss., 13, 3279-3322, 2013
www.atmos-chem-phys-discuss.net/13/3279/2013/
doi:10.5194/acpd-13-3279-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Ultrafine sea spray aerosol over the south eastern Pacific: open-ocean contributions to marine boundary layer CCN
R. Blot1, A. D. Clarke1,2, S. Freitag2, V. Kapustin1, S. G. Howell1, J. B. Jensen3, L. M. Shank1,*, C. S. McNaughton1,**, and V. Brekhovskikh1
1Department of Oceanography, University of Hawaii at Manoa, Hawaii, HI 96816, USA
2Department of Meteorology, University of Hawaii at Manoa, Hawaii, HI 96816, USA
3NCAR/EOL, Boulder, Colorado, USA
*now at: Pearl Harbor Naval Shipyard, Quality Assurance Division, JBPHH, HI 96860, USA
**now at: Golder Associates Ltd., Saskatoon, SK, Canada

Abstract. Accurate measurements of natural aerosol emissions over the ocean are needed to estimate the anthropogenic impact on the environment. In this study, we measured Sea Spray Aerosol (SSA) concentrations with diameters larger than 0.040 μm produced by open-ocean breaking waves over the SEP (South Eastern Pacific). Robust statistics were established through repeated airborne flights over 1000 km along 20° S from the coastline of Chile to 85° W during VOCALS-Rex (VAMOS Ocean-Cloud-Atmosphere-Land-Study Regional Experiment). Non-volatile SSA number concentrations were inferred using a thermally resolved technique constrained for clean conditions with Ångström exponent below 0.5, Black Carbon (BC) mass concentration at values lower than 15 ng m−3 and Organic aerosols (Org) concentration less than 0.02 μg m−3. We found that number concentrations of SSA active as CCN for a supersaturation of 0.25% varied between 17 cm−3 and 36 cm−3 but these did not increase with the increasing mean wind speed typically observed further offshore along 20° S. Concurrent increases in mean offshore precipitation rate in excess of about 1 mm d−1 indicate scavenging of SSA by precipitation exceeds increases in production at wind speeds above about 8 m s−1. This demonstrates the critical role of precipitation as a major sink of SSA over the remote ocean. Finally, we found that under clean conditions and for estimated stratus supersaturations between 0.20% and 0.43%, SSA represented about 20% of the total ambient CCN along 20° S.

Citation: Blot, R., Clarke, A. D., Freitag, S., Kapustin, V., Howell, S. G., Jensen, J. B., Shank, L. M., McNaughton, C. S., and Brekhovskikh, V.: Ultrafine sea spray aerosol over the south eastern Pacific: open-ocean contributions to marine boundary layer CCN, Atmos. Chem. Phys. Discuss., 13, 3279-3322, doi:10.5194/acpd-13-3279-2013, 2013.
 
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