Measuring site and meteorological situation
The Air Chemistry Observatory is installed approximately 1.5 km south of Neumayer III station which is located on the Ekström Ice shelf, about 8 km from the Atka Bay. During the summer months, the bay and the nearby coastline are mainly free of sea ice and there is always open water present.
The prevailing winds are from the East, but with strong switches to westerly winds from time to time. Northern wind directions are very rare, ensuring that the data are not subject to contamination from the base. Air masses advected to Neumayer generally passed over the continent for 2 to 3 days, but were marine before that.
Set-up and contamination control
The first Air Chemistry Observatory at Neumayer was initiated 1982 by the Institut für Umweltphysik, University of Heidelberg . Following almost 13 years of operation the technical equipment and the data acquisition facilities had to be modernised. The second and the present observatories were designed in collaboration of the University of Heidelberg and AWI, Bremerhaven, as a container building placed on a platform some meters above the snow.
Concerning anthropogenic pollutants, the Antarctic atmosphere is "ultra clean". Thus local pollution by vehicles and the base itself is a potential problem for many measurements concerning the background status of the antarctic troposphere. Consequently, a central aspect of the technical concept lies in the possibility of contamination-free sampling of aerosols and trace gases. This is realised by several means:
- The Air Chemistry Observatory is situated in a clean air facility approximately 1.5 km south of Neumayer. Due to the fact that northern wind directions are very rare, contamination from the base can be excluded for most of the time.
- The power supply (20 kW) is provided by cable from the main station, thus no fuel driven generator is operated in the vicinity.
- Contamination free sampling is controlled by the permanently recorded wind velocity, wind direction and by condensation nuclei (CN) concentration.
- Contamination is indicated if one of the following criteria is given: Wind direction within a 330°-30° sector, wind velocity <2.0 m/s or >18 m/s, or CN concentrations >2500 cm-3 during summer, >800 cm-3 during spring/autumn and >400 cm-3 during winter. If one or a definable combination of these criteria are given, high and low volume aerosol and part of the trace gas sampling will be interrupted.