Amsterdam Island (Territoire des Terres Australes et Antarctiques Francaises) is located in the South Indian Ocean at 5000 km off South Africa and 3500 off Australia. This is an old volcanic Island of 58 km2. There is no active volcanism and no regular marine or air traffic corridors in the vicinity of the island. The population is limited to about 20 people, living at the scientific base Martin de Vivies at about 2.5 km eastwards from the sampling site. The observatory is located in the Northern part of the island on the edge of a 55m high cliff. Air is sampled at the top of a 20m high tower. The surroundings of the sampling point at Pointe Benedicte are mainly composed of graminea. The site is under marine influence during most times of the year, and under southern Africa influence during some events in wintertime. To filtered out any local influence the data are selected when the winds arrive from a sector 260° to 300° with velocities higher than 8 m/s, or from a sector 300° to 360° with velocities higher or equal to 5 m/s.