Variability of mineral dust deposition in the western Mediterranean basin and south-east of France

Previous studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than 1 year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA (Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie in French) have been deployed in the western Mediterranean region during 1 to 3 years depending on the station. The sites include, from south to north, Lampedusa, Majorca, Corsica, Frioul and Le Casset (southern French Alps). Deposition measurements are performed on a common weekly period at the five sites. The mean dust deposition fluxes are higher close to the northern African coasts and decrease following a south-north gradient, with values from 7.4g m year in Lampedusa (35°31'N, 12°37'E) to 1g m year in Le Casset (44°59'N, 6°28'E). The maximum deposition flux recorded is of 3.2g m wk in Majorca with only two other events showing more than 1g m wk in Lampedusa, and a maximum of 0.5g m wk in Corsica. The maximum value of 2.1g m year observed in Corsica in 2013 is much lower than existing records in the area over the 3 previous decades (11 4g m year ). From the 537 available samples, 98 major Saharan dust deposition events have been identified in the records between 2011 and 2013. Complementary observations provided by both satellite and air mass trajectories are used to identify the dust provenance areas and the transport pathways from the Sahara to the stations for the studied period. Despite the large size of African dust plumes detected by satellites, more than 80% of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different deposition sites in the Mediterranean studied area. The results tend to indicate that wet deposition is the main form of deposition for mineral dust in the western Mediterranean basin, but the contribution of dry deposition (in the sense that no precipitation was detected at the surface) is far from being negligible, and contributes 10 to 46% to the major dust deposition events, depending on the sampling site. ' Author(s) 2016.This study was funded by the PRIMEQUALADEME programme on “Pollution atmosphérique longue distance” through the research project “Mesure du dépôt atmosphérique et validation de sa représentation dans les modèles régionaux” (DEMO project, contract no. 0962c0067). This project was also funded by the MISTRALS (Mediterranean Integrated Studies at Local and Regional Scales) programme as part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) and by the Spanish Government project ChArMEx: aerosols deposition ref: CTM2011-14036-E.Peer Reviewe

Variability of mineral dust deposition in the western Mediterranean basin and south-east of France

International audiencePrevious studies have provided some insight into the Saharan dust deposition at a few specific locations from observations over long time periods or intensive field campaigns. However, no assessment of the dust deposition temporal variability in connection with its regional spatial distribution has been achieved so far from network observations over more than 1 year. To investigate dust deposition dynamics at the regional scale, five automatic deposition collectors named CARAGA (Collecteur Automatique de Retombées Atmosphériques insolubles à Grande Autonomie in French) have been deployed in the western Mediterranean region during 1 to 3 years depending on the station. The sites include, from south to north, Lampedusa, Majorca, Corsica, Frioul and Le Casset (southern French Alps). Deposition measurements are performed on a common weekly period at the five sites. The mean dust deposition fluxes are higher close to the northern African coasts and decrease following a south-north gradient, with values from 7.4 g m −2 year −1 in Lampe-dusa (35 • 31 N, 12 • 37 E) to 1 g m −2 year −1 in Le Casset (44 • 59 N, 6 • 28 E). The maximum deposition flux recorded is of 3.2 g m −2 wk −1 in Majorca with only two other events showing more than 1 g m −2 wk −1 in Lampedusa, and a maximum of 0.5 g m −2 wk −1 in Corsica. The maximum value of 2.1 g m −2 year −1 observed in Corsica in 2013 is much lower than existing records in the area over the 3 previous decades (11-14 g m −2 year −1). From the 537 available samples, 98 major Saharan dust deposition events have been identified in the records between 2011 and 2013. Complementary observations provided by both satellite and air mass trajectories are used to identify the dust provenance areas and the transport pathways from the Sahara to the stations for the studied period. Despite the large size of African dust plumes detected Published by Copernicus Publications on behalf of the European Geosciences Union. 8750 J. Vincent et al.: Variability of mineral dust deposition by satellites, more than 80 % of the major dust deposition events are recorded at only one station, suggesting that the dust provenance, transport and deposition processes (i.e. wet vs. dry) of dust are different and specific for the different de-position sites in the Mediterranean studied area. The results tend to indicate that wet deposition is the main form of de-position for mineral dust in the western Mediterranean basin, but the contribution of dry deposition (in the sense that no precipitation was detected at the surface) is far from being negligible, and contributes 10 to 46 % to the major dust de-position events, depending on the sampling site