For a better understanding of the role of the terrestrial biosphere in the global cycle of greenhouse gases (GHGs), CGER has carried out aircraft observations over Siberia since 1992 in cooperation with Russian research institutions.

In the early stage of monitoring (1992 to 1994), observations focused on the horizontal distribution of GHGs over all of Siberia. Since 1993, the vertical distributions of GHGs have been measured by collecting air samples over three fixed sites in Siberia (Fig. 1 and Table 1).

Figure 1. Sampling sites and photographs of aircraft

Since July 1993, air sampling has been carried out once per month using chartered AN-24 aircraft at eight different altitudes between 0.5 and 7 km over the wetland near Surgut, West Siberia. The air is taken through the drain pipe in the cockpit and pressurized by a diaphragm pump up to about 0.2 MPa into Pyrex glass flasks each of 0.5 liter inner volume. The stop cocks of the glass flasks and the diaphragm pump are operated manually.

Air sampling over the forest area near Novosibirsk, West Siberia, has been conducted once per month since July 1997 using the AN-30 research aircraft operated by the Institute of Atmospheric Optics. Sampling procedures are almost the same as those conducted over Surgut.

Over the forest area near Yakutsk, East Siberia, air sampling has been done automatically at eight different altitudes between 0.5 and 5 km using AN-24 passenger aircraft since October 1996. The air is taken from the inlet tube installed at the bottom of the aircraft and pressurized by a diaphragm pump up to about 0.2 MPa into 0.75 liter glass flasks with pneumatic valves at both ends. The pneumatic valves are operated by a small board computer at the assigned altitudes detected by a pressure sensor. All these procedures are conducted during the ascent of the aircraft.