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

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 datapoor 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.

N2O Emissions From the Northern Benguela Upwelling System

“…Atmospheric N 2 O data were linearly interpolated over the time of the cruises and then used for the computation of the equilibrium concentrations, saturations, and sea-air fluxes of N 2 O. Our mean atmospheric N 2 O value (325.7 ± 1.82 ppb) was in good agreement with both flask data from the NOAA's Cooperative Globar Air Sampling Network (325.9 ± 0.38 ppb; 23.58 • S, 15.03 • E; Dlugokencky et al, 2014) and continuous measurements at the Namib Dessert Atmospheric Observatory (∼326 ppb; Morgan et al, 2015). N 2 O saturations (N 2 O sat ) were obtained from the concentration (C) ratio between seawater (sw) and atmospheric equilibrium (atm) values (N 2 O sat = C sw /C atm ·100).…”

Development of a Continuous Measurement System for Atmospheric O₂/N₂ Ratio Using a Paramagnetic Analyzer and Its Application in Minamitorishima Island, Japan

“…Therefore, we can observe variations in the atmospheric δ(O 2 /N 2 ) and CO 2 concentration simultaneously by our system with precision and time resolution comparable to those reported by past studies (e.g. Thompson et al 2009;Morgan et al 2015). Figure 3 shows the analytical δ(O 2 /N 2 ) results of a standard gas for 4.5 days, 2 minute running mean values of the corresponding signal outputs from the paramagnetic analyzer, and the ambient room temperature in our laboratory during the period.…”

“…To observe the O 2 /N 2 ratio continuously, a commercially available fuel cell analyzer (Sable Systems, Oxzilla FC-II) has been widely used in recent studies (e.g. Stephens et al 2007; Thompson et al 2009;Goto et al 2013;Morgan et al 2015). As summarized in a technical overview (Sable Systems International 2015), a paramagnetic analyzer has an unlimited life span, which is an advantage compared with a fuel cell analyzer that requires replacement of fuel cells nearly every 2 years.…”

Air–Sea Fluxes of Greenhouse Gases and Oxygen in the Northern Benguela Current Region During Upwelling Events

“…The instrument's internal pump was used to draw air through a 7 m length of 1/4" SERTOflex tubing, at a flow rate 150 mL min −1 . Inlets identical to those used at NDAO (Morgan et al, 2015) were placed on the starboard railing of the 6 th superstructure deck, just above the atmospheric chemistry lab, at a total height of ∼21 m above sea level. A second-order, instrument-specific water correction was performed in lieu of physical or chemical drying, identical to the method described in Morgan et al (2015).…”

“…Inlets identical to those used at NDAO (Morgan et al, 2015) were placed on the starboard railing of the 6 th superstructure deck, just above the atmospheric chemistry lab, at a total height of ∼21 m above sea level. A second-order, instrument-specific water correction was performed in lieu of physical or chemical drying, identical to the method described in Morgan et al (2015). As the instrument's pressure control seemed to be affected by strong vessel motion, measurements were excluded if the cavity pressure deviated by more than 0.04 torr.…”