A regional-to-global model of emission and transport of sea salt particles in the atmosphere

A parameterization for the emission of sea-salt aerosol (SSA) particles is presented and its application in the SILAM dispersion modeling system for regional and global SSA simulations is discussed. The SSA production term is based on the parameterization of Monahan et al. and on experimental data from Martensson et al., and Clarke et al. The observational data were used to extend the Monahan et al. SSA emission flux to particles as small as 10 nm (dry particle diameter D-P) and to account for water temperature and salinity. The result is an analytical formulation describing the SSA production fluxes for particles with D-P between 10 nm and 10 mu m. This source function is implemented in the dispersion model SILAM and applied to compute the distribution of sea salt over the North Atlantic and Western Europe for the years 2000, 2003, 2007, 2009 and 2010, as well as globally for 2001 and 2008. The computed annual global production of SSA is between 6700 and 7400 Tg/year. Comparison of the SILAM near-surface SSA concentrations and its wet deposition with the in situ EMEP observations showed good agreement for summer periods while in winter time the model tends to under-estimate the wet deposition by a factor of similar to 3. The underestimation is attributed to the coarse fraction (D-P > 10 mu m) and the spume production mechanism, which were excluded from the analysis, to the wet deposition parameterization in SILAM and to the under-estimated precipitation amount in the input meteodata. The predicted vertically integrated aerosol optical depth (AOD) showed a close match with satellite observations over SSA-dominated areas.