irm-EAMS (δ13C and δ15N)
CO2 in-air (δ13C and δ18O)
O2/N2 in air (+ δ18O of O2 in air or Ar/N2)
Laser Ablation
GasBench
TC/EA ('Pyrolysis', δ2H and δ18O)
Acid reaction and air mixing system (ARAMIS) (δ13C and δ18O)
O2/N2 in air
Complementary to the increase of CO2 in the atmosphere there is a decrease of O2. For every carbon atom burnt from fossil fuel one O2 molecule is lost to CO2. Atmospheric O2 has sources and sinks that differ largely from those of CO2. Thus, by studying the decrease of O2, i.e. measuring the O2/N2 ratio with high precision, a great deal can be learned about the global carbon cycle including the partitioning of sinks for CO2 between the oceans and the land biosphere.
Our mass spectrometric inlet system for measuring O2/N2 (and Ar/N2 or 34O/32O) ratios comprises a multiport valve, a drying tube and on open split from where air directly enters the mass spectrometer (Delta+XL with a collector assembly covering a simultaneous mass range from m/z 28 up to m/z 40). It is unique in terms of the sample consumption. Reliable measurements can be made from gas flows as low as 0.2 mL/min. Referencing is made in a very similar fashion as for CO2 in air by measuring versus an air reference and implementing a multiple referencing hierarchy system. The standardization scheme is complicated by the fact that an international reference has not been established, yet. Work on such a scale has started, with Ralph Keeling (Scripps Oceanic Institution, La Jolla) and Andrew Manning (BGC Jena) taking the lead. Our laboratory is one of the participants in this endeavour. Further results and improvements are described in
Willi A. Brand, O2/N2 Storage Aspects and Open Split Mass Spectrometric Determination, Proceedings of the 12th IAEA/WMO meeting of CO2 experts, Toronto, Sept. 2003, WMO-GAW Report 161, ed. D. Worthy 2005) (pdf)
In terms of precision, the analysis of O2/N2 ratios is very demanding. The above graph shows a long term quality control (including the necessary correction for CO+) of two cylinders with a nominal difference of 222 per meg.
Long term 1/2 hour O2/N2 and Ar/N2 measurements of reference tanks filled with dry air (before CO+ correction). Please note the short stabilisation times.
O2/N2 measurements from flasks: Issues of flask storage. The data were obtained using newly designed 1 l flasks with PCTFE seals, filled with dry air to a pressure of 2 bar (abs.). The flasks are now commercially available from Normag (Ilmenau, Germany, http://www.glasapparate.de/glaskolben.html
O2/N2 measurements from high pressure cylinders: All results are QA controlled using a set of 4 cylinders, one of them being assigned the working reference. Tanks that have not been used for a while exhibit some initial drift. All tank performances are within ± 2 permeg when initial drifts are removed except for L20010421 wich is not enclosed in a separate housing (commonly referrred to as the 'blue box'). Here the precision is ± 3.5 permeg