Influence of the source formulation on modeling the atmospheric global distribution of sea salt aerosol

Abstract

Abstract. Three different sea salt generation functions are investigated for use in global three-dimensional atmospheric models. Complementary observational data are used to validate an annual simulation of the whole size range (film, jet, and spume droplet derived particles). Aerosol concentrations are corrected for humidity growth and sampler inlet characteristics. Data from the North American deposition network are corrected for mineral dust to derive sea salt wet fluxes. We find that sea salt transport to inner continental areas requires substantial mass in the jet droplet range, which is best reproduced with the source of Monahah et al. [1986]. The results from this source formulation also shows the best agreement with aerosol concentration seasonality and sea salt size distributions below 4/•m dry radius. Measured wind speed dependence of coarse particle occurrence suggests that above 4/•m the source from Smith and Harrison [1998] is most appropriate. Such sea salt simulations are relevant for assessing heterogeneous chemistry and radiative effects. Sea salt aerosol provides on an annual average, in marine regions, an aggregate surface area equal to 1-10% of the area of the underlying Earth's surface. Together with mineral dust, sulfate, and carbonaceous aerosol the total aerosol surface area globally amounts to 13% of that of the Earth's surface. On the basis of atmospheric column burdens, sea salt represents 21% of the total global aerosol surface area. Equal partitioning of the aerosol surface area among the four components suggests that one has to consider all of them if the global aerosol impact is to be fully determined. IntroductionSea salt aerosol produced by the action of wind at the ocean surface constitutes the most abundant aerosol component together with mineral dust. Sea salt studies have addressed its impact on tropospheric chemistry, radiation balance, or air/sea exchange of matter and energy. The radius and the density of sea salt particles are largely affected by its hygroscopicity. We accounted for their evolution in time as a function of relative humidity (RH) conditions. At each model time step, for every grid box and size bin, radius and density were computed as a function of the mean dry radius and ECMWF three-dimensional (3-D) fields of specific humidity and temperature [see Gerber, 1988]. We assumed the particles to be spherical and to have the pure NaC1 ionic composition. Sea Salt Generation FunctionsTwo main mechanisms are thought to control sea salt formation: bubble bursting and tearing of wave crests by wind. Figures 2a and 2b). However, the annual number load is largest with Monahan (see also

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“…Natural emissions such as dimethylsulfide (DMS) emissions (Zubler et al, 2011) and sea salt (Guelle et al, 2001) emissions are computed interactively.…”

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