AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Ultrafine Sea Spray Aerosol over the South Eastern Pacific: Open-Ocean Contributions to Marine Boundary Layer CCN
Romain Blot, ANTONY CLARKE, Steffen Freitag, Vladimir Kapustin, Steven Howell, Jensen Jorgen, Lindsey Shank, Cameron McNaughton, Vera Brekhovskikh, University of Hawaii, Honolulu, HI 96822
Abstract Number: 197 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Accurate measurements of size resolved natural aerosol emissions over the ocean are needed for any relative assessment of the anthropogenic impact of aerosol on the environment or climate. However, isolating the Sea Spray Aerosol (SSA) production and removal flux under ambient marine condition down to sizes as small as 40 nm, those that usually contribute to cloud condensation nuclei (CCN) in marine clouds, has proven challenging. Here we report measured SSA concentrations with diameters larger than 40 nm 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 85W during the 2008 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 having a scattering Angtrom exponent below 0.5, Black Carbon (BC) mass concentrations less than 15 ngm-3 and Organic aerosols (Org) concentrations below 0.02 μgm-3. We found that number concentrations of SSA active as CCN for cloud supersaturation about 0.25 % varied between 17 cm-3 and 36 cm-3. However, SSA concentrations did not reveal the expected increase with the increasing mean wind speed encountered further offshore along 20S. Increases in precipitation scavenging of SSA for mean offshore precipitation rate in excess of about 1 mm d-1 appeared to exceed increased production for wind speeds increasing from about 8 – 14 ms-1. These observations demonstrate models of marine SSA and CCN concentrations must adequately represent both the SSA source and the critical role of precipitation as a major sink for SSA and CCN 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 20S.