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

E J Morgan,T Shuuya,K Vincent,A C Manning,J V Lavrič,J Sack,T Chicoine,M Heimann,T Seifert,R Logan,C Labuschagne,E G Uushona,A Day,S Schmidt,E.-G Brunke,R L Thompson,U Schultz,J Gomez

doi:10.5194/amt-8-2233-2015

Abstract

Abstract. A new coastal background site has been established for observations of greenhouse gases (GHGs) in the central Namib Desert at Gobabeb, Namibia. The location of the site was chosen to provide observations for a data-poor region in the global sampling network for GHGs. Semi-automated continuous measurements 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-down spectrometer (CRDS); nitrous oxide and carbon monoxide are measured with an off-axis integrated cavity output spectrometer (OA-ICOS). Instrument-specific water corrections are employed for both the CRDS and OA-ICOS instruments in lieu of drying. The performance and measurement uncertainties are discussed in detail. As the station is located in a remote desert environment, there are some particular challenges, namely fine dust, high diurnal temperature variability, and minimal infrastructure. The gas handling system and calibration scheme were tailored to best fit the conditions of the site. The CRDS and DFCA provide data of acceptable quality when base requirements for operation are met, specifically adequate temperature control in the laboratory and regular supply of electricity. In the case of the OA-ICOS instrument, performance is significantly improved through the implementation of a drift correction through frequent measurements of a reference cylinder.

Highlights

1.1 Background and motivationDue to their major role in global change and the climate system, time series of atmospheric greenhouse gases (GHGs) are a cornerstone of earth system science
We present some atmospheric potential oxygen (APO) data in this paper as a further evaluation of data quality since they are a synthesis of both atmospheric oxygen and carbon dioxide measurements
The cavity ring-down spectrometer (CRDS) and differential fuel cell analyzer (DFCA) are both housed in an insulated rack, which reduces the range of temperatures the devices are exposed to compared to the variation in the laboratory itself

Summary

Introduction

Due to their major role in global change and the climate system, time series of atmospheric greenhouse gases (GHGs) are a cornerstone of earth system science. Since the atmosphere is generally well mixed, the gradients and spatial variability of GHGs and other trace species can be quite small, necessitating high-quality, accurate, and precise measurements. The Southern Hemisphere is underrepresented relative to the Northern Hemisphere in the various sampling programs and networks of ground-based stations that make continuous measurements of GHGs (Tans et al, 1996; Rödenbeck et al, 2003; Marquis and Tans, 2012). Coverage is poor in Africa, which complicates efforts to monitor the variations and emissions of GHGs from developing economies, biomass burning, and the terrestrial biosphere (Valentini et al, 2014). Morgan et al.: Continuous measurements of GHGs in Namibia

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