Abstract

Abstract. A number of attempts have been made to incorporate sea-salt aerosol (SSA) source functions in chemistry transport models with varying results according to the complexity of the scheme considered. This contribution compares the inclusion of two different SSA algorithms in two chemistry transport models: CMAQ and CHIMERE. The main goal is to examine the differences in average SSA mass and composition and to study the seasonality of the prediction of SSA when applied to the Mediterranean area with high resolution for a reference year. Dry and wet deposition schemes are also analyzed to better understand the differences observed between both models in the target area. The applied emission algorithm in CHIMERE uses a semi-empirical formulation which obtains the surface emission rate of SSA as a function of the particle size and the surface wind speed raised to the power 3.41. The emission parameterization included within CMAQ is somehow more sophisticated, since fluxes of SSA are corrected with relative humidity. In order to evaluate their strengths and weaknesses, the participating algorithms as implemented in the chemistry transport models were evaluated against AOD measurements from Aeronet and available surface measurements in Southern Europe and the Mediterranean area, showing biases around −0.002 and −1.2 μg m−3, respectively. The results indicate that both models represent accurately the patterns and dynamics of SSA and its non-uniform behavior in the Mediterranean basin, showing a strong seasonality. The levels of SSA strongly vary across the Western and the Eastern Mediterranean, reproducing CHIMERE higher annual levels in the Aegean Sea (12 μg m−3) and CMAQ in the Gulf of Lion (9 μg m−3). The large difference found for the ratio PM2.5/total SSA in CMAQ and CHIMERE is also investigated. The dry and wet removal rates are very similar for both models despite the different schemes implemented. Dry deposition essentially follows the surface drag stress patterns, meanwhile wet deposition is more scattered over the continent. CMAQ tends to provide larger amounts of SSA dry deposition over the Northern Mediterranean (0.7–1.0 g m−2 yr−1), meanwhile the Southeastern Mediterranean accounts for the maximum annual dry deposition in the CHIMERE model (0.9–1.5 g m−2 yr−1). The wet deposition is dominated by the accumulation mode and is strongly correlated to the precipitation patterns, showing CMAQ a higher wet deposition/total deposition ratio over coastal mountain chains. The results of both models constitute a step towards increasing the understanding of the SSA dynamics in a complex area as the Mediterranean.

Highlights

  • Sea salt is the dominant aerosol mass component in the remote marine surface air and occasionally a significant one over the continents (Foltescu et al, 2005; Athanasopoulou et al, 2008)

  • The maximum concentration does not show a clear pattern, with the highest modeled sea-salt aerosol (SSA) concentrations located over open ocean (Atlantic and Mediterranean, above 55 μg m−3 reproduced by CMAQ); large differences appear in the location of the maxima (CMAQ-CHIMERE difference of −35 μg m−3 over the Aegean sea and +30 μg m−3 in the Northern Mediterranean basin)

  • This work compares two different algorithms implemented in CHIMERE and CMAQ chemistry transport models for representing SSA, highlighting the main differences found between them

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Summary

Introduction

Sea salt is the dominant aerosol mass component in the remote marine surface air and occasionally a significant one over the continents (Foltescu et al, 2005; Athanasopoulou et al, 2008). Despite a number of aerosol species is found in the atmosphere, including sulfate, black and organic carbon, mineral dust and sea salt (Haywood et al, 1999; Solmon et al, 2006; Zakey et al, 2006), on a global scale, the total mass of natural aerosols is much higher than that of anthropogenically produced types of aerosols (Lewis and Schwartz, 2004). Fewer studies have investigated sea-salt production at the regional scale (e.g., Tindale and Pease, 1999; Vinoj and Satheesh, 2004; Foltescu et al, 2005; Athanasopoulou et al, 2008; Zakey et al, 2008, among others)

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