February 2008

Measurements of atmospheric ozone/nitrogen ratio in air at
Cape Point, South Africa

In September 2007, sampling equipment for the analysis of ozone/nitrogen, argon/nitrogen and carbon dioxide was installed at the Cape Point Global Atmosphere Watch (GAW) station in South Africa. The Cape Point GAW station, which is being managed by the South African Weather Service, is the latest addition to a global network of ozone sampling sites. This programme constitutes a collaborative venture between Princeton University and the South African Weather Service.

The flask sampler has been modified so that it will automatically fill two glass canisters with air when baseline conditions prevail. The filled flasks are then analysed for ozone/nitrogen and argon/nitrogen ratios at Princeton and thereafter sent to the Earth Systems Research Laboratory, NOAA, Boulder, Colorado, where they are also analysed for carbon dioxide and possibly other trace gases.

map of Cape Point   instrument
Geographic location of Cape Point GAW station   Removing filled flasks from sampler

The primary aim of this study is to measure atmospheric ozone/nitrogen over a two-year period in order to determine the amplitude and phase of the annual cycle of this property. It will also aid in improving the assessment of oceanic vs. terrestrial biospheric uptake of fossil fuel carbon dioxide and will shed more light on the out-gassing process of the ocean. This information, together with carbon dioxide data (already collected at Cape Point) since 1993, will then be used, along with data from other sites, to constrain net community production of ocean ecosystems upwind of Cape Point, i.e. in the South Atlantic Ocean and the Atlantic sector of the Southern Ocean. An ancillary project involves measuring the argon/nitrogen ratios on the same samples.

All in all, the data collected should provide urgently needed information on the sink strength of the Southern Ocean with regard to carbon dioxide uptake. Recent modelling studies have already indicated that the capacity of the oceanic region south of Africa to take up carbon dioxide is declining.

South African Air Quality Information System



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