• Planète et Univers/Océan, Atmosphère
  
• Sciences de l'ingénieur/Mécanique/Mécanique des fluides
  
• Physique/Mécanique/Mécanique des fluides
  

Aerosol particles in coastal areas result from a complex mixing between sea spray aerosols locally generated at the sea surface by the wind-waves interaction processes and a continental component resulting from natural and/or anthropogenic sources. This paper presents a physical and chemical analysis of the aerosol data acquired from May to September 2014 in the Adriatic Sea. Aerosol distributions were measured on the Acqua Alta platform located 15 km off the coast of Venice using two Particle Measuring System probes and a chemical characterization was made using an Ion Chromatography analysis (IC). Our aim is to study both the sea-spray contribution and the anthropogenic influence in the coastal aerosol of this Mediterranean region. To this end, we focus on a comparison between the present data and the aerosol size distributions measured south of the French Mediterranean coast. For air masses of marine origin transported by southern winds on the French coast and by the Sirocco in the Adriatic, we note a good agreement between the concentrations of super-micrometer aerosols measured in the two locations. This indicates a similar sea surface production of sea-spray aerosols formed by bubble bursting processes in the two locations. In contrast, the results show larger concentrations of submicron particles in the North-Western Mediterranean compared to the Adriatic, which result probably from a larger anthropogenic background for marine conditions. In contrast, for a coastal influence, the chemical analysis presented in the present paper seems to indicate a larger importance of the anthropogenic impact in the Northern Adriatic compared to the West-Northern Mediterranean.

The knowledge of the swash zone is of primary importance to understand the morphological evolution of sedimentary beaches. The swash zone is highly dynamic, with instantaneous sediment fluxes often being several orders of magnitude greater than their surf zone counterparts. Despite of the increased research efforts dedicated to the swash hydro- and morphodynamics during the last decades, several key processes remain to be understood before the swash morphodynamics can be predicted and modeled. A large part of existing studies have focused on meso to macrotidal swash zones exposed to moderate to storm wave conditions. The present communication reports on a field study of small-scale swash bed processes in microtidal and small wave conditions. It is shown that even such calm conditions can result in significantly dynamic swash zone. The selected field site is the Pont de Rousty sandy beach, Camargue, France. A high-resolution survey of the swash zone sand bed has been performed over a cross-shore transect on both hydro and morphodynamic aspects. The instrumentation included a set of both buried and non-buried pressure sensors, a network of ultrasonic altimeters, a 3D high resolution acoustic velocimeter and other pressure and velocity sensors deployed outside the swash zone to measure the incoming forcing. Results show that the swash bed and slope permanently evolve under the action of waves. Each swash event can individually induce bed level variations ranging from 1 to 5mm but larger evolution (up to 4cm) are observed at longer time scales. Ongoing work is focused, on one hand, to the role played by the swash physical parameters (velocity, duration, height, etc) on the event-related transport and, on the other hand, to the identification of a " bottom-up " relationship between the succession of individual actions of swash events and the long term evolution of swash morphology.

Aerosol particles in coastal areas result from a complex mixing between sea-spray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. This paper presents physicochemical characterisation of aerosols observed during meteorological conditions characteristics of coastal areas. In particular, we study the influence of sea-breezes and land-breezes as well as the fetch variation, which superpose on larger synoptic conditions, on aerosol properties. This was achieved using a physical, chemical and optical analysis of the aerosol data acquired in May 2007 on the French Mediterranean coast. The aerosol distributions were measured using a TSI SMPS 3081 model and the chemical characterization was made using an Ion Chromatography analysis (IC) and a thermo-optical technique. In addition, aerosol optical characteristics were provided by aethalometer (absorption) and nephelometer (scattering) measurements. For low wind speeds, we detect high aerosol number concentrations as well as high NO3- and carbonaceous compounds contributions, which are observed even when the aerosol is sampled in pure maritime air masses. These results indicate that air masses are strongly impacted by pollution transported over the Mediterranean. In addition, the combination of low wind speeds and land/sea breezes lead to the production of new ultrafine particle formation events that seem to take place over the sea before being transported back to the coast. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are significantly lowered due to the dispersion of anthropogenic pollutants. Optical measurements reveal that mean scattering and absorbing coefficients are about 15.2 Mm-1 and 3.6 Mm-1, respectively. Associated mean aerosol single scattering albedo is found to be about 0.87 and 0.94 (at 520 nm) for continental and maritime influences.