Direct air measurements using the high resolution Thermo Ultra mass spectrometer: O2/N2 and Ar/N2 ratios, and O2, N2 and Ar isotopic composition

I will present a newly developed method for analyzing major air components and their isotopic composition, using the high resolution Thermo Ultra mass spectrometer. The main characteristics of this instrument that are interesting in this context are the high resolution, stability and sensitivity. The high resolution results in fewer isobaric interferences; low abundance compounds (e.g. multiply substituted molecules) can be observed due to the high resolution and high sensitivity; and the instrument stability allows long measurements, as needed for obtaining high precision for the low abundance compounds.The species that can be analyzed so far with useful precision are:- O2/N2 and Ar/N2 (precision in permeg range)- O2 isotopologues, including clumped: 16O2, 16O17O, 16O18O, 17O18O, 18O2- N2 isotopologues, including clumped: 14N2, 14N15N, 15N2- Ar isotopes: 36Ar, 38Ar, 40ArThe whole suite of measurements uses about 10 ml of dry air, and takes up to two days for one sample.The first application of this method is planned for stratospheric and icecore samples.