Cryospheric studies of atmospheric trends in stratospherically and radiatively important gases

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Mass spectrometric analyses of permanent gas elemental and isotope ratios will be made on firn air and ice from drilling campaigns, and firn air from year-round studies, including the following: Elemental ratios: O2/N2, Ar/N2, Ar/O2, Ne/Ar, Kr/Ar, Xe/Ar Isotope ratios: d15N(N2), d17O(O2), d18O(O2), d36Ar, isotopes of Ne, Kr, Xe Radioactive gases: 85Kr Deviations from fractionation due to gravitational separation will be examined near the snow surface and at the firn-ice transition. In the former mixing and separation is controlled by convective airflows and thermal diffusion. In the latter fractionation may occur by non-laminar gas flows through microporous structures, close off of firn pores or by firn pumping. Meteorological and physical parameters in conjunction with trace gas profiles will be the basis for quantifying gas mixing in the upper firn strata. Overlapping analysis of firn air and ice within and below the firn-ice transition will allow studies of possible fractionation processes there. These processes will be incorporated in to the firn diffusion models.

CRYOSTAT will provide measurements of many trace species and will quantify their radiative forcing. In addition, the Kyoto Protocol of the UN Framework Convention on Climate Change, and similar policy instruments and industry, require quantification of the global warming potential for many gases produced as a result of human activity. For both these reasons it is important to have accurate values of the radiative efficiencies (i.e. Watts per square metre per ppbv) for the trace species. We have concentrated on a number of species for which there are significant discrepancies in the literature. For HFC134a, HFC23, HFC227ea and HFC32, we performed an inter-comparison of model results with researchers in Norway and reached a consensus forcing, which differed significantly from some previously published results. We were then involved in a wider inter-comparison of the forcing of HFC-134a, carried out for an Special Report of the Intergovernmental Panel on Climate Change. For CF4, we worked with two separate groups performing laboratory measurements of the absorption cross-section, after we recognised an unusually wide spread in the values obtained in previous measurements. The new measurements agreed within their error bars and this led to a proposed radiative efficiency 25% higher than listed in IPCC Scientific Assessments. All the above results have been published in the peer-reviewed literature. More recently we have performed calculations of the radiative efficiencies of several heavier per fluorocarbons, including c-C4F8, for which time trends in concentration have been derived by CRYOSTAT for the first time.

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