Continuous measurements of greenhouse gases and atmospheric oxygen at the Namib Desert Atmospheric Observatory

摘要

A new coastal background site has been established for observations ofgreenhouse gases (GHGs) in the central Namib Desert at Gobabeb, Namibia. Thelocation of the site was chosen to provide observations for a data-poorregion in the global sampling network for GHGs. Semi-automated continuousmeasurements of carbon dioxide, methane, nitrous oxide, carbon monoxide,atmospheric oxygen, and basic meteorology are made at a height of 21 m a.g.l.,50 km from the coast at the northern border of the Namib Sand Sea.Atmospheric oxygen is measured with a differential fuel cell analyzer (DFCA).Carbon dioxide and methane are measured with an early-model cavity ring-downspectrometer (CRDS); nitrous oxide and carbon monoxide are measured with anoff-axis integrated cavity output spectrometer (OA-ICOS). Instrument-specificwater corrections are employed for both the CRDS and OA-ICOS instruments inlieu of drying. The performance and measurement uncertainties are discussedin detail. As the station is located in a remote desert environment, thereare some particular challenges, namely fine dust, high diurnal temperaturevariability, and minimal infrastructure. The gas handling system andcalibration scheme were tailored to best fit the conditions of the site. TheCRDS and DFCA provide data of acceptable quality when base requirements foroperation are met, specifically adequate temperature control in thelaboratory and regular supply of electricity. In the case of the OA-ICOSinstrument, performance is significantly improved through the implementationof a drift correction through frequent measurements of a reference cylinder.