Assessment of a multi-species in situ FTIR for precise atmospheric greenhouse gas observations

Abstract

Abstract. We thoroughly evaluate the performance of a multi-species, in situ Fourier transform infrared (FTIR) analyser with respect to high-accuracy needs for greenhouse gas monitoring networks. The in situ FTIR analyser is shown to measure CO2, CO, CH4 and N2O mole fractions continuously, all with better reproducibility than the inter-laboratory compatibility (ILC) goals, requested by the World Meteorological Organization (WMO) for the Global Atmosphere Watch (GAW) programme. Simultaneously determined δ13CO2 reaches reproducibility as good as 0.03‰. Second-order dependencies between the measured components and the thermodynamic properties of the sample, (temperature, pressure and flow rate) and the cross sensitivities among the sample constituents are investigated and quantified. We describe an improved sample delivery and control system that minimises the pressure and flow rate variations, making post-processing corrections for those quantities non-essential. Temperature disequilibrium effects resulting from the evacuation of the sample cell are quantified and improved by the usage of a faster temperature sensor. The instrument has proven to be linear for all measured components in the ambient concentration range. The temporal stability of the instrument is characterised on different time scales. Instrument drifts on a weekly time scale are only observed for CH4 (0.04 nmol mol−1 day−1) and δ13CO2 (0.02‰ day−1). Based on 10 months of continuously collected quality control measures, the long-term reproducibility of the instrument is estimated to ±0.016 μmol mol−1 CO2, ±0.03‰ δ13CO2, ±0.14 nmol mol−1 CH4, ±0.1 nmol mol−1 CO and ±0.04 nmol mol−1 N2O. We propose a calibration and quality control scheme with weekly calibrations of the instrument that is sufficient to reach WMO-GAW inter-laboratory compatibility goals.

Comparison of nitrous oxide (N<sub>2</sub>O) analyzers for high-precision measurements of atmospheric mole fractions

“…Over the last few years, new analytical techniques have become commercially available for obtaining high-precision measurements of atmospheric N 2 O. Hammer et al (2013) described the Fourier transform infrared (FTIR) absorption, which can reach a long-term repeatability (LTR) for N 2 O of 0.04 ppb over a 10-month period. More recently, laser-based systems, e.g., cavity-enhanced off-axis integrated cavity output spectroscopy (OA-ICOS), cavity ring-down spectroscopy (CRDS), quantum cascade tunable infrared laser differential absorption spectroscopy (QC-TILDAS) and difference frequency generation (DFG)-based systems, were developed and commercialized by different companies.…”

“…The LSCE purchased this analyzer (built by Ecotech, Australia) in 2011 from the University of Wollongong (Australia). Detailed descriptions of similar analyzers used in the atmospheric community are presented by Griffith et al (2012) and Hammer et al (2013). The instrument used in our laboratory consists of a commercially available FTIR interferometer (IRcube, Bruker Optics, Germany) with a 1 cm −1 resolution coupled to a 3.5 L multi-pass glass cell with a 24 m optical path length (PA-24, Infrared Analysis, USA).…”

Inverse modelling of European CH<sub>4</sub> emissions during 2006–2012 using different inverse models and reassessed atmospheric observations

“…These measurements have been rigorously qualitycontrolled within the InGOS project. The quality control includes regular measurements of target gases that monitor instrument performance and long-term stability (Hammer et al, 2013;Lopez et al, 2015;Schmidt et al, 2014;WMO, 1993). The instrument precision has been evaluated as a 24 h moving 1σ standard deviation of bracketing working standards (denoted "working standard repeatability").…”

Estimation of continuous anthropogenic CO<sub>2</sub>: model-based evaluation of CO<sub>2</sub>, CO, δ<sup>13</sup>C(CO<sub>2</sub>) and Δ<sup>14</sup>C(CO<sub>2</sub>) tracer methods

“…Zondervan and Meijer (1996), Pataki et al (2006) and Djuricin et al (2010) attempted to estimate fuel CO 2 emissions in specific case studies using mass spectrometric measurements of δ 13 C(CO 2 ), in addition to 14 C(CO 2 ) measurements. Recently, new optical instrumentation allows for δ 13 C(CO 2 ) to be measured continuously (e.g., Esler et al, 2000;Tuzson et al, 2011;Hammer et al, 2013;Vogel et al, 2013a), thus opening the door for δ 13 C(CO 2 ) as a continuous tracer for fuel CO 2 contributions. In order to use δ 13 C(CO 2 ) measurements at an urban site, the mean isotopic signature of the sources (and sinks) in the catchment area of the site, δ F , must be known (Newman et al, 2015) and relatively constant and potentially require calibration (as discussed for CO).…”