The joint German-Japanese-Swedish AGAMES (Antarctic Trace Gas and Aerosol Airborne Measurement Study) aircraft field experiment was conducted during the Antarctic summer season December/January 2006/07. It represents a unique effort by delivering the first ever comprehensive atmospheric aerosol measurements over Antarctica using an airplane as an observational platform. The objectives of the experiment are:

• Characterization of the tropospheric aerosol physical, chemical and optical properties, its vertical distribution, transport pathways and life cycle over coastal Antarctica as well as above the continental ice sheet.
• Investigate composition and mixing state of atmospheric aerosol by means of size segregated volatility measurements and single particle analysis.
• Investigate the origin of aerosol particles deposited on the Antarctic Plateau with special emphasis on the relative importance of local sources, long-range transport and stratosphere-troposphere exchange.
• Investigate to what extent ground-based long-term monitoring measurements at Syowa, Neumayer, Troll, Aboa and Wasa/Svea stations are representative on a regional/continental scale.

In general, aerosols consist of a mixture of tiny particles suspended in the air, having special physical and chemical properties that depend on sources, transport and deposition processes in the atmosphere as well as on their size distribution and concentration. Aerosol effects on atmospheric radiation remain a point of major uncertainty in understanding past and present climates and in predicting the future climate. The particles have a direct influence on the atmosphere by scattering and absorbing solar and terrestrial short-wave and long-wave radiation. This may lead to heating or cooling depending on the aerosol properties, the surface albedo, and the cloud cover. They also indirectly effect the radiation and the water budget of the atmosphere by influencing cloud characteristics. Furthermore they are part of many heterogeneous chemical reaction chains. With respect to climate, the importance of the polar regions reaches far beyond our present civilization as ice cores provide information about long-term variations in aerosols and trace gases.

To assess present, past and future impacts of aerosols in a changing atmosphere we need to understand the processes that determine the physical and chemical character of the aerosol particles at a particular place and time. The knowledge about aerosol properties and distribution over Antarctica is fairly limited and based only on relatively few ground-based measurements. They are mostly confined to the coastal regions, which are to a large degree influenced by marine aerosol originating from the surrounding Southern Ocean. Origin and properties of the aerosol over the Antarctic plateau, which reaches elevations of more than 3 km, are much less clear. Gas to particle conversion of the sulphur bearing gases of marine origin is likely to play a role, as well as long-range transport of aerosol particles via the middle and upper troposphere. The aerosol vertical distribution in the Antarctic troposphere, and therefore aerosol transport patterns and life cycle in general, cannot be sufficiently described based on ground-based observations alone. This gap in knowledge also considerably limits the ability to decipher Antarctic ice core records of past climate and palaeoenvironments. Furthermore, detailed understanding of the air–snow transfer of aerosol particles requires knowledge of their chemical composition as well as concentration and size distribution.

Research platforms and observations

The AGAMES experiment took place in December 2006 and January 2007. The base for the first half of the project was the German Antarctic base Georg von Neumayer (70°39’S, 8°15’ W). The second half of the experiment was based at the summer field camp S17 (69°01’S, 40°06’E) located approximately 30 km east of the Japanese station Syowa.

The aircraft used in this study was a Dornier 228-200 turboprop (POLAR 2) belonging to the Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven. Altogether 36 flights were performed mainly between Neumayer and Syowa between 20 December 2006 and 26 January 2007. Measurements were also carried out during ferry flights between Neumayer and Syowa (Camp S17) with stops at the Russian station Novolazarevskaya and the Belgian station Belaren. Information in respect of the aerosol properties and vertical distribution deep over the continental ice sheet were obtained during two flights operating with refuelling stops at the German station Kohnen (75°S, 4°E) (picture 1). Typical duration of the flights was between 2 and 3 hours with flights operating at an altitude range from surface (picture 2) up to 7 300 m. In total, almost 100 hours of airborne data is available. With an average cruising speed of around 80 m/s a distance close to 30 000 km was covered.

The scientific instrumentation on board the POLAR 2 aircraft delivered measurements of aerosol number density for particles of various sizes. Several instruments located inside the cabin as well as mounted directly on the aircraft wing delivered aerosol size distribution between 0.004 and 30 μm. In addition, aerosol light scattering and light absorption properties were also measured. Aerosol chemical composition was investigated in two ways. The size dependent measurements of the mixing state of aerosol particles were accompanied by filter sampling for consecutive analysis of the single particle chemical composition using scanning and transmission electron microscope techniques. Populations of aerosol particles can be formed by aerosols of the same composition (homogeneously mixed aerosol) or by particles of different composition (heterogeneously mixed aerosol). Information about the single particle composition and mixing state can be used to shed light on the origin and age of the aerosol particles and to assist in assessing the degree of contribution from natural and anthropogenic sources, as well as local and long-range transported aerosol.

Data analysis is currently in progress, but already even at this early stage interesting information about the Antarctic tropospheric aerosol has become apparent. It has been found that the vertical variability of aerosol concentrations is relatively small if compared to mid-latitude observations, but the vertical distribution is less homogeneous than expected based on earlier data. Aerosol layers or distinct vertical gradients in aerosol concentrations were observed during several flights. This feature is especially pronounced for accumulation mode particles, where strong enhancement was repeatedly observed in the upper troposphere.

The AGAMES project represents an important contribution in our effort to better understand atmospheric aerosol distribution and properties and the role they play in the climate system. Our long-term strategy is to gain knowledge about their sources and sinks, transport and transformation processes, and their interactions with clouds and climate on a global pole-to-pole scale.