Atmospheric carbon dioxide and its stable isotope ratios, methane, carbon monoxide, nitrous oxide and hydrogen from Shetland Isles

Since November 1992, 0.5 glass flasks have been filled approximately monthly with dry marine air from Shetland Isles, Scotland (60.2°N, 1.2°W) and transported to CSIRO, Australia for analyses. The Shetland site is part of a CSIRO global flask network with 10–12 sites, anchored to continuous high precision in situ measurements made at the Australian Cape Grim Baseline Station (40.7°S, 144.7°E), a primary station in the Global Atmosphere Watch programme (GAW) coordinated by the World Meteorological Organisation. The methodology is summarised, and Shetland results for CO2, CH4, N2O, CO, H2 and δ13C, δ18O of CO2 presented for the period 1992–1996. We compare data to available results from surrounding stations of the NOAA cooperative network (in particular Mace Head, Ireland, 53.3°N, 9.9°W), and address issues of both trace species intercalibration and atmospheric spatial gradients. While considerable uniformity of trace-gas composition is evident in oceanic air over a 13° range of latitude, nevertheless anomalies in CO2 concentration and isotopic composition are suggested in samples representing air to the west of Shetland. The potential for remotely monitoring integrated emissions from northern Europe is also identified.