A sea spray aerosol flux parameterization encapsulating wave state

J Ovadnevaite,A Manders,G De Leeuw,C D O'Dowd,A.-I Partanen,H Korhonen,C Monahan,D Ceburnis

doi:10.5194/acp-14-1837-2014

Abstract

Abstract. A new sea spray source function (SSSF), termed Oceanflux Sea Spray Aerosol or OSSA, was derived based on in-situ sea spray aerosol measurements along with meteorological/physical parameters. Submicron sea spray aerosol fluxes derived from particle number concentration measurements at the Mace Head coastal station, on the west coast of Ireland, were used together with open-ocean eddy correlation flux measurements from the Eastern Atlantic Sea Spray, Gas Flux, and Whitecap (SEASAW) project cruise. In the overlapping size range, the data for Mace Head and SEASAW were found to be in a good agreement, which allowed deriving the new SSSF from the combined dataset spanning the dry diameter range from 15 nm to 6 μm. The OSSA source function has been parameterized in terms of five lognormal modes and the Reynolds number instead of the more commonly used wind speed, thereby encapsulating important influences of wave height, wind history, friction velocity, and viscosity. This formulation accounts for the different flux relationships associated with rising and waning wind speeds since these are included in the Reynolds number. Furthermore, the Reynolds number incorporates the kinematic viscosity of water, thus the SSSF inherently includes dependences on sea surface temperature and salinity. The temperature dependence of the resulting SSSF is similar to that of other in-situ derived source functions and results in lower production fluxes for cold waters and enhanced fluxes from warm waters as compared with SSSF formulations that do not include temperature effects.

Highlights

Sea spray aerosol (SSA) is an important component of the aerosol population in the marine environment, and given that 70 % of the Earth’s surface is covered by oceans, it contributes significantly to the global aerosol budget (Vignati et al, 2010)
The OSSA-spray aerosol source functions (SSSF) has been evaluated by comparing the resulting sea spray aerosol mass with independent HR-ToFAMS measurements at Mace Head, which were not used in the derivation of the OSSA-SSSF
The largest discrepancy between the SSA mass fluxes obtained with the OSSA-SSSF and measured with the HR-ToF-AMS is due to the large uncertainty in super-micron aerosol distributions since SSA particles in this size range have the highest contribution to the SSA mass

Summary

Introduction

Sea spray aerosol (SSA) is an important component of the aerosol population in the marine environment, and given that 70 % of the Earth’s surface is covered by oceans, it contributes significantly to the global aerosol budget (Vignati et al, 2010). Sea spray aerosol particles are formed at the sea surface mainly through breaking waves via bubble bursting (Blanchard, 1963) and, at elevated wind speeds, by direct tearing of wave crests (Monahan et al, 1986). The nearsurface wind speed, commonly measured and expressed at a reference height of 10 m, U10, is thought to be the dominant factor affecting sea spray aerosol production. Different formulations of the size-dependent sea spray aerosol source functions (SSSF) in terms of only U10 vary widely for the same U10 (de Leeuw et al, 2011) and rising or waning winds produce different production fluxes (Callaghan et al, 2008; Goddijn-Murphy et al, 2011; Norris et al, 2012; Ovadnevaite et al, 2012). Considerable effort has been devoted to linking SSA production to more fundamentally relevant physical parameters, such as wind stress on the surface, or whitecap fraction, with the expectation that such

Results

Discussion

Conclusion