Submicron Sea Salt Aerosol Inside and Outside of the Surf Plume: Size Segregated and Total Sea salt Aerosol Distributions by Single Particle Analysis at a Coastal Marine Site

HR: 0800h
AN: A31C-0082 [Abstracts]
TI: Submicron Sea Salt Aerosol Inside and Outside of the Surf Plume: Size Segregated and Total Sea salt Aerosol Distributions by Single Particle Analysis at a Coastal Marine Site
AU: * Campuzano-Jost, P
EM: pcampuzano@rsmas.miami.edu
AF: RSMAS/MAC, 4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Donohoue, D
EM: ddonohoue@rsmas.miami.edu
AF: RSMAS/MAC, 4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Maring, H B
EM: hmaring@rsmas.miami.edu
AF: RSMAS/MAC, 4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Hynes, A J
EM: ahynes@rsmas.miami.edu
AF: RSMAS/MAC, 4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AB: The uncertainties in the shape of the source function for sea salt aerosols as well as in the of the shape of the size distribution of sea salt aerosol in the marine boundary layer (MBL) are considered, after even greater uncertainties for dust aerosol, the biggest open question to assess the impact of aerosols on climate change [1]. In a recent intercomparison of global models, satellite retrievals and ground-based measurements, Kinne et al [2] found large discrepancies between simulated and measured aerosol extinction in the Southern Ocean, and suggested that this might be indicative of an underestimation of the contribution of submicron sea salt aerosol in current models. Although since at least Murphy et al's [3] the importance of submicron sea salt aerosol in the clean MBL for radiative forcing is recognized, high quality data on the size distribution and on the source function of sea salt in this size range is sparse. Field measurements from O'Dowd et al and Clarke et al [4,5], based on the aerosol volatility technique, yielded contrasting results in the two size regions crucial for direct and indirect forcing. We have developed a sea salt specific aerosol particle sizer [6,7], the Aerosol Sodium Detector (ASD), that in its current, improved version is able to quantitatively measure the amount of sea salt in single aerosol particles using sodium as a proxy in the range between 1 fg NaCl equivalent (95 nm NaCl dry diameter) and 7000 fg NaCl equivalent (1800 nm diameter) with a sizing accuracy better than 5% and no losses within the valid detection range. This instrument was deployed at a coastal site at Bellows AFB in Oahu, Hawaii to study the contribution of sea salt to the total aerosol load in both remote marine air and the surf zone at wind speeds up to 10 m/s. Full sea salt number size distributions were acquired continuously in 2 s samples and matched the results of a commercial aerodynamic particle sizer down to 400 nm better than 20% in all cases. The distributions showed a main submicron mode at 520 nm dry diameter as well as a second mode below 300 nm that was strongly enhanced in breaking waves, in agreement with Clarke et al's recent findings [5]. Total sea salt particle count down to the detection limit was about 12-14 part/cc at 9.5 m/s u10. In size-segregated mode, the extent of internal mixing of surf zone aerosol was monitored. The results were consistent with pure sea salt with little processing down to the detection limit of 100 nm. Average size dependent sea salt mixing ratios were calculated, with sea salt being the primary aerosol component down to 200 nm, in good agreement with Murphy et al's reported ratios [3]. The results of this study suggest a much larger contribution to total aerosol scattering by sea salt aerosols in remote marine air than current parameterizations of the sea salt size distribution imply [4,8]. They also hint at a very effective removal process of very small sea salt particles ($<$200 nm) formed in breaking waves in the MBL. References: 1.Penner, J. et al.,in: 3rd IPCC Report, 2001, Cambridge University Press: Cambridge. p.289-348. 2.Kinne, S. et al., J. Geophys. Res.-Atmos., 2003. 108(D20). 3.Murphy, D.M. et al., Nature, 1998, 392(6671): p.62-65. 4.O'Dowd, C.D. et al., Atmos. Environ., 1997, 31(1): p.73-80. 5.Clarke, A.D. et al., J. Atmos. Ocean. Tech., 2003, 20(10): p.1362-1374. 6.Clark, C.D. et al., J. Aerosol Sci., 2001, 32(6):p.765-778. 7.Campuzano-Jost, P. et al., J. Atmos. Ocean. Tech., 2003, 20(10):p.1421-1430. 8.Gong, S.L., Global Biogeochem. Cy., 2003, 17(4).
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0360 Transmission and scattering of radiation
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting