Vogel, B., Ekman, A.

Kristina Lundgren

Sea salt particles have an impact on the global and regional climate by influencing factors such as atmospheric radiation, cloud formation and atmospheric heterogeneous chemistry. For this reason the aim of this study is to introduce a parameterization describing the emission of sea salt particles from the sea surface to the atmosphere for the regional atmospheric predicting model LM‐ART. The particles are assumed to be emitted as dry particles and stay in this way during transport. The sea salt emission‐parameterization is composed by three parameterizations describing the emission of particles with dry particle diameter Dp between 0.02 μm and 28 μm as a function of the 10‐meter level wind speed and the sea surface temperature. It is seen that the amount of emitted particles with a dry particle diameter less than 1 μm increases with decreasing sea surface temperature while the opposite occurs for particles larger than 0.4 μm. The emission of sea salt particles increases with increasing wind speed. The large particles influence the total mass concentration the most, while the small particles have the largest influence on the total number concentration. For May 28‐29th, 2005 3‐D simulations over an area west of Ireland were performed examining the horizontal and vertical distribution of mass and number concentration of particles as function of temperature, wind speed and time. It is found that both number and mass concentration of sea salt particles are highly dependent on wind speed. Maximum reached mass concentration during this period is 300 μg m‐3 and in number concentration 100 cm‐3. The maximum values both occur when the wind speed over the ocean is strongest. The transport over land is significant for the sea salt particles and it is found that the smallest particles dominate over larger particles over land since the number concentration is large also over land but the mass concentration decreases rapidly over land. Also the vertical mixing of sea salt particles is seen to be most effective for the smallest particles (in the sub micrometer size range). The differences in efficiency in transport of particles are mainly because of varying residence time in the troposphere, longer residence time for the smaller particles and shorter for the larger particles. Interaction with radiation, atmospheric chemistry or cloud processes are not taken into account in this work and will be the aim of future studies.